Add a function x_chance_in_y(x,y) to replace the various

random2(y) < x checks, e.g. x_chance_in_y(weight, totalweight). This
should make things a bit more readable. Apply it to a number of files.


git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6428 c06c8d41-db1a-0410-9941-cceddc491573

28 files changed, 248 insertions, 237 deletions

diff --git a/crawl-ref/source/abyss.cc b/crawl-ref/source/abyss.cc
index bf8167dcab..7d9a427909 100644
--- a/crawl-ref/source/abyss.cc
+++ b/crawl-ref/source/abyss.cc
@@ -735,7 +735,7 @@ static void _apply_corruption_effect( map_marker *marker, int duration)
 
     for (int i = 0; i < neffects; ++i)
     {
-        if (random2(4000) < cmark->duration
+        if (x_chance_in_y(cmark->duration, 4000)
             && !_spawn_corrupted_servant_near(cmark->pos))
         {
             break;
diff --git a/crawl-ref/source/cloud.cc b/crawl-ref/source/cloud.cc
index aca3710b42..24b62e6977 100644
--- a/crawl-ref/source/cloud.cc
+++ b/crawl-ref/source/cloud.cc
@@ -120,7 +120,7 @@ static void _dissipate_cloud(int cc, cloud_struct &cloud, int dissipate)
     // Apply calculated rate to the actual cloud.
     cloud.decay -= dissipate;
 
-    if (random2(100) < cloud.spread_rate)
+    if (x_chance_in_y(cloud.spread_rate, 100))
     {
         cloud.spread_rate -= div_rand_round(cloud.spread_rate, 10);
         cloud.decay       -= _spread_cloud(cloud);
diff --git a/crawl-ref/source/clua.cc b/crawl-ref/source/clua.cc
index 7107dc6355..8ada60d847 100644
--- a/crawl-ref/source/clua.cc
+++ b/crawl-ref/source/clua.cc
@@ -2010,7 +2010,7 @@ static int crawl_random_element(lua_State *ls)
         if (rollsize > 0)
         {
             rollsize += this_weight;
-            if (random2(rollsize) < this_weight)
+            if (x_chance_in_y(this_weight, rollsize))
             {
                 lua_pushvalue(ls, key_idx);
                 lua_replace(ls, value_idx);
diff --git a/crawl-ref/source/decks.cc b/crawl-ref/source/decks.cc
index 17e6c65210..de5e5c5a62 100644
--- a/crawl-ref/source/decks.cc
+++ b/crawl-ref/source/decks.cc
@@ -374,7 +374,7 @@ static card_type _choose_from_archetype(const deck_archetype* pdeck,
     {
         const card_with_weights& cww = pdeck[i];
         totalweight += cww.weight[rarity];
-        if (random2(totalweight) < cww.weight[rarity])
+        if (x_chance_in_y(cww.weight[rarity], totalweight))
             result = cww.card;
     }
     return result;
@@ -820,7 +820,7 @@ bool deck_peek()
         already_seen++;
 
     // Always increase if seen 2, 50% increase if seen 1.
-    if (already_seen && random2(2) < already_seen)
+    if (already_seen && x_chance_in_y(already_seen, 2))
         deck.props["non_brownie_draws"]++;
 
     mprf("You draw two cards from the deck. They are: %s and %s.",
@@ -1197,12 +1197,13 @@ void evoke_deck( item_def& deck )
     if (you.penance[GOD_NEMELEX_XOBEH])
     {
         int c = 1;
-        if ( (flags & (CFLAG_MARKED | CFLAG_SEEN))
-             || props["num_marked"].get_byte() > 0 )
+        if ((flags & (CFLAG_MARKED | CFLAG_SEEN))
+            || props["num_marked"].get_byte() > 0)
         {
             c = 3;
         }
-        if (random2(3000) < c * you.penance[GOD_NEMELEX_XOBEH])
+
+        if (x_chance_in_y(c * you.penance[GOD_NEMELEX_XOBEH], 3000))
         {
             card_type old_card = card;
             card = _choose_from_archetype(deck_of_punishment, rarity);
@@ -1268,7 +1269,7 @@ void evoke_deck( item_def& deck )
     }
 
     if (!deck_gone && allow_id
-        && (you.skills[SK_EVOCATIONS] > 5 + random2(35)))
+        && you.skills[SK_EVOCATIONS] > 5 + random2(35))
     {
         mpr("Your skill with magical items lets you identify the deck.");
         set_ident_flags( deck, ISFLAG_KNOW_TYPE );
@@ -1292,11 +1293,11 @@ int get_power_level(int power, deck_rarity_type rarity)
     case DECK_RARITY_COMMON:
         break;
     case DECK_RARITY_LEGENDARY:
-        if (random2(500) < power)
+        if (x_chance_in_y(power, 500))
             ++power_level;
         // deliberate fall-through
     case DECK_RARITY_RARE:
-        if (random2(700) < power)
+        if (x_chance_in_y(power, 700))
             ++power_level;
         break;
     }
@@ -1434,8 +1435,8 @@ static void _damnation_card(int power, deck_rarity_type rarity)
     if (you.religion == GOD_NEMELEX_XOBEH && !player_under_penance())
         nemelex_bonus = you.piety / 20;
 
-    int extra_targets = power_level + random2(you.skills[SK_EVOCATIONS] +
-                                              nemelex_bonus) / 12;
+    int extra_targets = power_level + random2(you.skills[SK_EVOCATIONS]
+                                              + nemelex_bonus) / 12;
 
     for (int i = 0; i < 1 + extra_targets; ++i)
     {
@@ -1588,7 +1589,7 @@ static int _drain_monsters(int x, int y, int pow, int garbage)
         {
             simple_monster_message(&mon, " is drained.");
 
-            if (random2(20) < pow/60)
+            if (x_chance_in_y(pow / 60, 20))
             {
                 mon.hit_dice--;
                 mon.experience = 0;
@@ -1805,7 +1806,7 @@ static void _helm_card(int power, deck_rarity_type rarity)
         {
             // If there are n left, of which we need to choose
             // k, we have chance k/n of selecting the next item.
-            if ( random2(4-i) < num_resists )
+            if (x_chance_in_y(num_resists, 4-i))
             {
                 // Add a temporary resistance.
                 you.duration[possible_resists[i]] += random2(power/7) + 1;
@@ -2171,9 +2172,10 @@ static void _sage_card(int power, deck_rarity_type rarity)
 
         if (you.skills[i] < MAX_SKILL_LEVEL)
         {
-            const int curweight = 1 + you.skills[i] * (40-you.skills[i]) * c;
+            // Choosing a skill is likelier if you are little skilled in it.
+            const int curweight = 1 + you.skills[i] * (40 - you.skills[i]) * c;
             totalweight += curweight;
-            if (random2(totalweight) < curweight)
+            if (x_chance_in_y(curweight, totalweight))
                 result = i;
         }
     }
@@ -2183,8 +2185,8 @@ static void _sage_card(int power, deck_rarity_type rarity)
     else
     {
         you.duration[DUR_SAGE] = random2(1800) + 200;
-        you.sage_bonus_skill = static_cast<skill_type>(result);
-        you.sage_bonus_degree = power / 25;
+        you.sage_bonus_skill   = static_cast<skill_type>(result);
+        you.sage_bonus_degree  = power / 25;
         mprf(MSGCH_PLAIN, "You feel studious about %s.", skill_name(result));
     }
 }
@@ -2275,7 +2277,8 @@ static void _water_card(int power, deck_rarity_type rarity)
 static void _glass_card(int power, deck_rarity_type rarity)
 {
     const int power_level = get_power_level(power, rarity);
-    const int radius = (power_level == 2) ? 1000 : random2(power/40) + 2;
+    const int radius = (power_level == 2) ? 1000
+                                          : random2(power/40) + 2;
     vitrify_area(radius);
 }
 
@@ -2825,7 +2828,7 @@ bool card_effect(card_type which_card, deck_rarity_type rarity,
         if (coinflip())
         {
             mprf("You have drawn %s.", card_name(which_card));
-            your_spells(SPELL_OLGREBS_TOXIC_RADIANCE,random2(power/4), false);
+            your_spells(SPELL_OLGREBS_TOXIC_RADIANCE, random2(power/4), false);
         }
         else
             rc = _damaging_card(which_card, power, rarity);
diff --git a/crawl-ref/source/dungeon.cc b/crawl-ref/source/dungeon.cc
index 96c521479f..927e8fc600 100644
--- a/crawl-ref/source/dungeon.cc
+++ b/crawl-ref/source/dungeon.cc
@@ -1530,8 +1530,8 @@ static void _place_base_islands(int margin, int num_islands, int estradius,
         {
             centre_ok = true;
 
-            centres[i].x = a + random2(GXM-2*a-1);
-            centres[i].y = b + random2(GYM-2*b-1);
+            centres[i].x = a + random2(GXM - 2*a - 1);
+            centres[i].y = b + random2(GYM - 2*b - 1);
 
             for (int j = 0; j < i; ++j)
             {
@@ -1544,7 +1544,7 @@ static void _place_base_islands(int margin, int num_islands, int estradius,
                     break;
                 }
             }
-            if (random2(num_islands) && island_distance)
+            if (island_distance && !one_chance_in(num_islands))
                 --island_distance;
         }
         while (!centre_ok);
@@ -1589,27 +1589,27 @@ static void _prepare_shoals(int level_number)
 
     // Adding shallow water at deep water adjacent to floor.
     // Randomisation: place shallow water if at least 1d(1d3) floor neighbours
-    for ( int i = margin; i < GXM - margin; ++i)
-        for ( int j = margin; j < GYM - margin; ++j)
+    for (int i = margin; i < GXM - margin; ++i)
+        for (int j = margin; j < GYM - margin; ++j)
             if (grd[i][j] == DNGN_DEEP_WATER
                 && count_neighbours(i, j, DNGN_FLOOR) > random2(random2(3)+1))
             {
                 grd[i][j] = DNGN_SHALLOW_WATER;
             }
 
-    // Placing sandbanks
+    // Placing sandbanks.
     for (int banks = 0; banks < 8; ++banks)
     {
-        int xsize = 3+random2(3);  // random rectangle
-        int ysize = 3+random2(3);
+        int xsize = 3 + random2(3);  // random rectangle
+        int ysize = 3 + random2(3);
         int xb = random2(GXM - 2 * margin - 10) + margin + 2;
         int yb = random2(GYM - 2 * margin - 10) + margin + 2;
 
         bool ok_place = true;
-        for ( int i = xb; i < xb + xsize; ++i )
-            for ( int j = yb; j < yb + ysize; ++j )
+        for (int i = xb; i < xb + xsize; ++i)
+            for (int j = yb; j < yb + ysize; ++j)
             {
-                if ( grd[i][j] != DNGN_DEEP_WATER )
+                if (grd[i][j] != DNGN_DEEP_WATER)
                     ok_place = false;
             }
 
@@ -1639,7 +1639,7 @@ static void _prepare_shoals(int level_number)
                 if ( grd[x][y] == DNGN_DEEP_WATER )
                 {
                     int badness = count_neighbours(x, y, DNGN_WATER_STUCK);
-                    if ( random2(badness) >= 2 && coinflip() )
+                    if (random2(badness) >= 2 && coinflip())
                         grd[x][y] = DNGN_LAVA;
                 }
 
@@ -1770,7 +1770,8 @@ static void _prepare_water( int level_number )
                                 grd[i][j] = DNGN_SHALLOW_WATER;
                             }
                             else if (which_grid >= DNGN_FLOOR
-                                     && random2(100) < 80 - level_number * 4)
+                                     && x_chance_in_y(80 - level_number * 4,
+                                                      100))
                             {
                                 grd[i][j] = DNGN_SHALLOW_WATER;
                             }
@@ -2085,7 +2086,7 @@ static void _place_minivaults(const std::string &tag, int lo, int hi, bool force
     }
 
     int chance = you.your_level == 0? 50 : 100;
-    while (chance && random2(100) < chance || nvaults-- > 0)
+    while (chance && x_chance_in_y(chance, 100) || nvaults-- > 0)
     {
         const int vault = _dgn_random_map_for_place(true);
         if (vault == -1)
@@ -2223,7 +2224,8 @@ static builder_rc_type _builder_basic(int level_number)
     int doorlevel  = random2(11);
     int corrlength = 2 + random2(14);
     int roomsize   = 4 + random2(5) + random2(6);
-    int no_corr = (one_chance_in(100) ? 500 + random2(500) : 30 + random2(200));
+    int no_corr = (one_chance_in(100) ? 500 + random2(500)
+                                      : 30 + random2(200));
     int intersect_chance = (one_chance_in(20) ? 400 : random2(20));
 
     _make_trail( 35, 30, 35, 20, corrlength, intersect_chance, no_corr,
@@ -2287,7 +2289,7 @@ static builder_rc_type _builder_basic(int level_number)
         }
     }
 
-    // make some more rooms:
+    // Make some more rooms.
     no_rooms = 1 + random2(3);
     max_doors = 1;
 
@@ -2798,7 +2800,7 @@ static bool _make_room(int sx,int sy,int ex,int ey,int max_doors, int doorlevel)
             && grid_is_solid(grd[sx-1][ry-1])
             && grid_is_solid(grd[sx-1][ry+1]))
         {
-            if (random2(10) < doorlevel)
+            if (x_chance_in_y(doorlevel, 10))
                 grd[sx-1][ry] = DNGN_CLOSED_DOOR;
         }
 
@@ -2807,7 +2809,7 @@ static bool _make_room(int sx,int sy,int ex,int ey,int max_doors, int doorlevel)
             && grid_is_solid(grd[ex+1][ry-1])
             && grid_is_solid(grd[ex+1][ry+1]))
         {
-            if (random2(10) < doorlevel)
+            if (x_chance_in_y(doorlevel, 10))
                 grd[ex+1][ry] = DNGN_CLOSED_DOOR;
         }
     }
@@ -2820,7 +2822,7 @@ static bool _make_room(int sx,int sy,int ex,int ey,int max_doors, int doorlevel)
             && grid_is_solid(grd[rx-1][sy-1])
             && grid_is_solid(grd[rx+1][sy-1]))
         {
-            if (random2(10) < doorlevel)
+            if (x_chance_in_y(doorlevel, 10))
                 grd[rx][sy-1] = DNGN_CLOSED_DOOR;
         }
 
@@ -2829,7 +2831,7 @@ static bool _make_room(int sx,int sy,int ex,int ey,int max_doors, int doorlevel)
             && grid_is_solid(grd[rx-1][ey+1])
             && grid_is_solid(grd[rx+1][ey+1]))
         {
-            if (random2(10) < doorlevel)
+            if (x_chance_in_y(doorlevel, 10))
                 grd[rx][ey+1] = DNGN_CLOSED_DOOR;
         }
     }
@@ -5212,7 +5214,7 @@ static void _place_pool(dungeon_feature_type pool_type, unsigned char pool_x1,
     if (pool_x1 >= pool_x2 - 4 || pool_y1 >= pool_y2 - 4)
         return;
 
-    left_edge = pool_x1 + 2 + random2(pool_x2 - pool_x1);
+    left_edge  = pool_x1 + 2 + random2(pool_x2 - pool_x1);
     right_edge = pool_x2 - 2 - random2(pool_x2 - pool_x1);
 
     for (j = pool_y1 + 1; j < pool_y2 - 1; j++)
@@ -5980,7 +5982,7 @@ static char _plan_3()
             const int prev_ry2 = romy2[which_room - 1];
 
             join_the_dots( coord_def(rx1 + random2( rx2 - rx1 ),
-                                      ry1 + random2( ry2 - ry1 )),
+                                     ry1 + random2( ry2 - ry1 )),
                             coord_def(prev_rx1 + random2(prev_rx2 - prev_rx1),
                                       prev_ry1 + random2(prev_ry2 - prev_ry1)),
                             MMT_VAULT );
@@ -6010,7 +6012,7 @@ static char _plan_3()
                 const int prev_ry2 = romy2[i - 1];
 
                 join_the_dots( coord_def( rx1 + random2( rx2 - rx1 ),
-                                           ry1 + random2( ry2 - ry1 ) ),
+                                          ry1 + random2( ry2 - ry1 ) ),
                                 coord_def(
                                     prev_rx1 + random2( prev_rx2 - prev_rx1 ),
                                     prev_ry1 + random2( prev_ry2 - prev_ry1 ) ),
@@ -6904,8 +6906,8 @@ static void _big_room(int level_number)
 
         if (level_number > 7)
         {
-            type_floor = ((random2(level_number) < 14) ? DNGN_DEEP_WATER
-                                                       : DNGN_LAVA);
+            type_floor = (x_chance_in_y(14, level_number) ? DNGN_DEEP_WATER
+                                                          : DNGN_LAVA);
         }
 
         octa_room(sr, oblique, type_floor);
@@ -6923,8 +6925,8 @@ static void _big_room(int level_number)
 
     if (level_number > 7 && one_chance_in(4))
     {
-        type_floor = ((random2(level_number) < 14) ? DNGN_DEEP_WATER
-                                                   : DNGN_LAVA);
+        type_floor = (x_chance_in_y(14, level_number) ? DNGN_DEEP_WATER
+                                                      : DNGN_LAVA);
     }
 
     // Make the big room.
@@ -7032,15 +7034,15 @@ static void _roguey_level(int level_number, spec_room &sr, bool make_stairs)
         _replace_area( rox1[i], roy1[i], rox2[i], roy2[i],
                        DNGN_ROCK_WALL, DNGN_FLOOR );
 
-        // inner room?
+        // Inner room?
         if (rox2[i] - rox1[i] > 5 && roy2[i] - roy1[i] > 5
-            && random2(100 - level_number) < 3)
+            && x_chance_in_y(3, 100 - level_number))
         {
             if (!one_chance_in(4))
             {
                 _box_room( rox1[i] + 2, rox2[i] - 2, roy1[i] + 2,
                            roy2[i] - 2, (coinflip() ? DNGN_STONE_WALL
-                                                       : DNGN_ROCK_WALL) );
+                                                    : DNGN_ROCK_WALL) );
             }
             else
             {
@@ -7078,17 +7080,17 @@ static void _roguey_level(int level_number, spec_room &sr, bool make_stairs)
             {
             case 0:
                 last_room = i - 1;
-                pos[0] = rox1[i];      // - 1;
-                pos[1] = roy1[i] + random2(roy2[i] - roy1[i]);
+                pos[0]  = rox1[i];      // - 1;
+                pos[1]  = roy1[i] + random2(roy2[i] - roy1[i]);
                 jpos[0] = rox2[last_room];      // + 1;
                 jpos[1] = roy1[last_room]
-                                + random2(roy2[last_room] - roy1[last_room]);
+                            + random2(roy2[last_room] - roy1[last_room]);
                 break;
 
             case 1:
                 last_room = i - 5;
-                pos[1] = roy1[i];      // - 1;
-                pos[0] = rox1[i] + random2(rox2[i] - rox1[i]);
+                pos[1]  = roy1[i];      // - 1;
+                pos[0]  = rox1[i] + random2(rox2[i] - rox1[i]);
                 jpos[1] = roy2[last_room];      // + 1;
                 jpos[0] = rox1[last_room]
                                 + random2(rox2[last_room] - rox1[last_room]);
@@ -7697,10 +7699,10 @@ bool dgn_region::overlaps(const map_mask &mask) const
 coord_def dgn_region::random_edge_point() const
 {
     return random2(size.x + size.y) < size.x ?
-              coord_def( pos.x + random2(size.x),
-                         coinflip()? pos.y : pos.y + size.y - 1 )
-            : coord_def( coinflip()? pos.x : pos.x + size.x - 1,
-                         pos.y + random2(size.y) );
+                  coord_def( pos.x + random2(size.x),
+                             coinflip()? pos.y : pos.y + size.y - 1 )
+                : coord_def( coinflip()? pos.x : pos.x + size.x - 1,
+                             pos.y + random2(size.y) );
 }
 
 coord_def dgn_region::random_point() const
diff --git a/crawl-ref/source/effects.cc b/crawl-ref/source/effects.cc
index 3b0c21128e..26d2847bef 100644
--- a/crawl-ref/source/effects.cc
+++ b/crawl-ref/source/effects.cc
@@ -888,7 +888,7 @@ static int _find_acquirement_subtype(object_class_type class_wanted,
             const int weight = you.skills[i] + 1;
             count += weight;
 
-            if (random2(count) < weight)
+            if (x_chance_in_y(weight, count))
                 skill = i;
         }
 
@@ -909,7 +909,7 @@ static int _find_acquirement_subtype(object_class_type class_wanted,
             if (wskill == SK_THROWING)
                 wskill = weapon_skill(OBJ_WEAPONS, i);
 
-            if (wskill == skill && random2(count += acqweight) < acqweight)
+            if (wskill == skill && x_chance_in_y(acqweight, count += acqweight))
                 type_wanted = i;
         }
     }
@@ -923,7 +923,7 @@ static int _find_acquirement_subtype(object_class_type class_wanted,
             if (you.skills[i])
             {
                 count += you.skills[i];
-                if (random2(count) < you.skills[i])
+                if (x_chance_in_y(you.skills[i], count))
                     skill = i;
             }
         }
@@ -1309,10 +1309,10 @@ static int _find_acquirement_subtype(object_class_type class_wanted,
                     while (you.had_book[type_wanted]);
                 }
 
-                // if the book is invalid find any valid one.
+                // If the book is invalid find any valid one.
                 while (book_rarity(type_wanted) == 100
-                                       || type_wanted == BOOK_DESTRUCTION
-                                       || type_wanted == BOOK_MANUAL)
+                       || type_wanted == BOOK_DESTRUCTION
+                       || type_wanted == BOOK_MANUAL)
                 {
                     type_wanted = random2(NUM_BOOKS);
                 }
@@ -1436,11 +1436,13 @@ static int _find_acquirement_subtype(object_class_type class_wanted,
 
             case OBJ_MISCELLANY:
                 do
+                {
                     type_wanted = random2(NUM_MISCELLANY);
+                }
                 while (type_wanted == MISC_HORN_OF_GERYON
-                    || type_wanted == MISC_RUNE_OF_ZOT
-                    || type_wanted == MISC_CRYSTAL_BALL_OF_FIXATION
-                    || type_wanted == MISC_EMPTY_EBONY_CASKET);
+                       || type_wanted == MISC_RUNE_OF_ZOT
+                       || type_wanted == MISC_CRYSTAL_BALL_OF_FIXATION
+                       || type_wanted == MISC_EMPTY_EBONY_CASKET);
                 break;
             default:
                 break;
@@ -2210,7 +2212,7 @@ static void _hell_effects()
     else if (temp_rand > 7) // 10 in 27 odds {dlb}
     {
         // 60:40 miscast:summon split {dlb}
-        summon_instead = (random2(5) > 2);
+        summon_instead = x_chance_in_y(2, 5);
 
         switch (you.where_are_you)
         {
@@ -2486,11 +2488,11 @@ void handle_time(long time_delta)
     // about 1.5 points on average, so they can corrupt the player
     // quite quickly.  Wielding one for a short battle is OK, which is
     // as things should be.   -- GDL
-    if (you.duration[DUR_INVIS] && random2(10) < 6)
+    if (you.duration[DUR_INVIS] && x_chance_in_y(6, 10))
         added_contamination++;
 
     if (you.duration[DUR_HASTE] && !you.duration[DUR_BERSERKER]
-        && random2(10) < 6)
+        && x_chance_in_y(6, 10))
     {
         added_contamination++;
     }
@@ -2637,7 +2639,7 @@ void handle_time(long time_delta)
             break;
         }
 
-        if (random2(100) < total_skill)
+        if (x_chance_in_y(total_skill, 100))
         {
             item_def& item = you.inv[you.equip[EQ_WEAPON]];
 
@@ -3016,7 +3018,7 @@ void update_corpses(double elapsedTime)
     }
 
     int fountain_checks = static_cast<int>(elapsedTime / 1000.0);
-    if (random2(1000) < static_cast<int>(elapsedTime) % 1000)
+    if (x_chance_in_y(static_cast<int>(elapsedTime) % 1000, 1000))
         fountain_checks += 1;
 
     // dry fountains may start flowing again
diff --git a/crawl-ref/source/fight.cc b/crawl-ref/source/fight.cc
index 0864f666bc..18be80e265 100644
--- a/crawl-ref/source/fight.cc
+++ b/crawl-ref/source/fight.cc
@@ -112,7 +112,7 @@ bool test_melee_hit(int to_hit, int ev)
 
     if (to_hit >= AUTOMATIC_HIT)
         return (true);
-    else if (random2(100) < MIN_HIT_MISS_PERCENTAGE)
+    else if (x_chance_in_y(MIN_HIT_MISS_PERCENTAGE, 100))
         margin = (coinflip() ? 1 : -1) * AUTOMATIC_HIT;
     else
     {
@@ -247,15 +247,17 @@ int calc_heavy_armour_penalty( bool random_factor )
         }
     }
 
-    // heavy armour modifiers for PARM_EVASION
+    // Heavy armour modifiers for PARM_EVASION.
     if (you.equip[EQ_BODY_ARMOUR] != -1)
     {
         const int ev_pen = property( you.inv[you.equip[EQ_BODY_ARMOUR]],
                                      PARM_EVASION );
 
-        if (ev_pen < 0 &&
-            maybe_random2(you.skills[SK_ARMOUR], random_factor) < abs(ev_pen))
+        if (ev_pen < 0 && maybe_random2(you.skills[SK_ARMOUR],
+                                        random_factor) < abs(ev_pen))
+        {
             heavy_armour += maybe_random2( abs(ev_pen), random_factor );
+        }
     }
 
     // ??? what is the reasoning behind this ??? {dlb}
@@ -273,14 +275,14 @@ int calc_heavy_armour_penalty( bool random_factor )
             heavy_armour /= 2;
         }
     }
-    return heavy_armour;
+    return (heavy_armour);
 }
 
 static bool player_fights_well_unarmed(int heavy_armour_penalty)
 {
     return (you.burden_state == BS_UNENCUMBERED
-            && random2(20) < you.skills[SK_UNARMED_COMBAT]
-            && random2(1 + heavy_armour_penalty) < 2);
+            && x_chance_in_y(you.skills[SK_UNARMED_COMBAT], 20)
+            && x_chance_in_y(2, 1 + heavy_armour_penalty));
 }
 
 unchivalric_attack_type is_unchivalric_attack(const actor *attacker,
diff --git a/crawl-ref/source/it_use2.cc b/crawl-ref/source/it_use2.cc
index 8953c4eb1c..3f6e8df4b3 100644
--- a/crawl-ref/source/it_use2.cc
+++ b/crawl-ref/source/it_use2.cc
@@ -81,7 +81,7 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
         mpr("You feel much better.");
 
         // only fix rot when healed to full
-        if ( you.hp == you.hp_max)
+        if (you.hp == you.hp_max)
         {
             unrot_hp( (2 + random2avg(5, 2)) / factor );
             set_hp(you.hp_max, false);
@@ -148,7 +148,7 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
         mprf(MSGCH_DURATION, "You feel %s all of a sudden.",
              were_mighty ? "mightier" : "very mighty");
 
-        if ( were_mighty )
+        if (were_mighty)
             contaminate_player(1, was_known);
         else
             modify_stat(STAT_STRENGTH, 5, true, "");
@@ -180,8 +180,8 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
         break;
 
     case POT_LEVITATION:
-        mprf("You feel %s buoyant.",
-             (!player_is_airborne()) ? "very" : "more");
+        mprf("You feel %s buoyant.", !player_is_airborne() ? "very"
+                                                           : "more");
 
         if (!player_is_airborne())
             mpr("You gently float upwards from the floor.");
@@ -228,8 +228,8 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
         break;
 
     case POT_INVISIBILITY:
-        mpr( (!you.duration[DUR_INVIS]) ? "You fade into invisibility!"
-             : "You fade further into invisibility." );
+        mpr(!you.duration[DUR_INVIS] ? "You fade into invisibility!"
+                                     : "You fade further into invisibility.");
 
         // Invisibility cancels backlight.
         you.duration[DUR_BACKLIGHT] = 0;
@@ -260,11 +260,14 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
         break;
 
     case POT_DEGENERATION:
-        if ( pow == 40 )
+        if (pow == 40)
             mpr("There was something very wrong with that liquid!");
+
         if (lose_stat(STAT_RANDOM, (1 + random2avg(4, 2)) / factor, false,
                       "drinking a potion of degeneration"))
+        {
             xom_is_stimulated(64 / factor);
+        }
         break;
 
     // Don't generate randomly - should be rare and interesting.
@@ -320,7 +323,7 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
             nothing_happens = false;
         }
 
-        // give a message if no message otherwise
+        // Give a message if no message otherwise.
         if (!restore_stat(STAT_ALL, 0, false) && nothing_happens)
             mpr( "You feel refreshed." );
         break;
@@ -331,7 +334,7 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
             mpr("You feel slightly irritated.");
             make_hungry(100, false);
         }
-        else if ( you.duration[DUR_BUILDING_RAGE] )
+        else if (you.duration[DUR_BUILDING_RAGE])
         {
             you.duration[DUR_BUILDING_RAGE] = 0;
             mpr("Your blood cools.");
@@ -346,7 +349,7 @@ bool potion_effect( potion_type pot_eff, int pow, bool was_known )
     case POT_CURE_MUTATION:
         mpr("It has a very clean taste.");
         for (int i = 0; i < 7; i++)
-            if (random2(10) > i)
+            if (x_chance_in_y(i, 10))
                 delete_mutation(RANDOM_MUTATION, false);
         break;
 
@@ -614,8 +617,6 @@ void unwear_armour(char unw)
 
     if (is_random_artefact( you.inv[unw] ))
         unuse_randart(unw);
-
-    return;
 }
 
 void unuse_randart(unsigned char unw)
diff --git a/crawl-ref/source/it_use3.cc b/crawl-ref/source/it_use3.cc
index 58949f87a8..a247b568f5 100644
--- a/crawl-ref/source/it_use3.cc
+++ b/crawl-ref/source/it_use3.cc
@@ -170,10 +170,10 @@ void special_wielded()
     case SPWLD_VARIABLE:
         do_uncurse_item( you.inv[wpn] );
 
-        if (random2(5) < 2)     // 40% chance {dlb}
+        if (x_chance_in_y(2, 5))     // 40% chance {dlb}
             you.inv[wpn].plus  += (coinflip() ? +1 : -1);
 
-        if (random2(5) < 2)     // 40% chance {dlb}
+        if (x_chance_in_y(2, 5))     // 40% chance {dlb}
             you.inv[wpn].plus2 += (coinflip() ? +1 : -1);
 
         if (you.inv[wpn].plus < -4)
@@ -206,14 +206,14 @@ void special_wielded()
         break;
 
     case SPWLD_POWER:
-        you.inv[wpn].plus = stepdown_value( -4 + (you.hp / 5), 4, 4, 4, 20 );
+        you.inv[wpn].plus  = stepdown_value( -4 + (you.hp / 5), 4, 4, 4, 20 );
         you.inv[wpn].plus2 = you.inv[wpn].plus;
         break;
 
     case SPWLD_OLGREB:
         // Giving Olgreb's staff a little lift since staves of poison have
         // been made better. -- bwr
-        you.inv[wpn].plus = you.skills[SK_POISON_MAGIC] / 3;
+        you.inv[wpn].plus  = you.skills[SK_POISON_MAGIC] / 3;
         you.inv[wpn].plus2 = you.inv[wpn].plus;
         break;
 
@@ -248,8 +248,6 @@ void special_wielded()
     {
         you.wield_change = true;
     }
-
-    return;
 }                               // end special_wielded()
 
 static bool _reaching_weapon_attack(const item_def& wpn)
@@ -310,7 +308,7 @@ static bool _reaching_weapon_attack(const item_def& wpn)
         {
             const int skill = weapon_skill( wpn.base_type, wpn.sub_type );
 
-            if ((5 + (3 * skill)) > random2(40))
+            if (x_chance_in_y(5 + (3 * skill), 40))
             {
                 mpr("You reach to attack!");
                 success = you_attack(mgrd[beam.tx][beam.ty], false);
@@ -326,6 +324,7 @@ static bool _reaching_weapon_attack(const item_def& wpn)
             mpr("You reach to attack!");
             success = you_attack(mgrd[beam.tx][beam.ty], false);
         }
+
         if (success)
         {
             int mid = mgrd[beam.tx][beam.ty];
@@ -353,7 +352,6 @@ static bool evoke_horn_of_geryon()
         mpr("You produce a weird and mournful sound.");
 
         for (int count_x = 0; count_x < GXM; count_x++)
-        {
             for (int count_y = 0; count_y < GYM; count_y++)
             {
                 if (grd[count_x][count_y] == DNGN_STONE_ARCH)
@@ -373,7 +371,6 @@ static bool evoke_horn_of_geryon()
                     }
                 }
             }
-        }
 
         if (rc)
             mpr("Your way has been unbarred.");
@@ -385,17 +382,17 @@ static bool evoke_horn_of_geryon()
             mgen_data(MONS_BEAST, BEH_HOSTILE,
                       4, you.pos(), MHITYOU));
     }
-    return rc;
+    return (rc);
 }
 
 static bool evoke_sceptre_of_asmodeus()
 {
     bool rc = true;
-    if ( one_chance_in(21) )
+    if (one_chance_in(21))
         rc = false;
-    else if (one_chance_in(2))
+    else if (coinflip())
     {
-        // summon devils, maybe a Fiend
+        // Summon devils, maybe a Fiend.
         const monster_type mtype = (one_chance_in(4) ? MONS_FIEND :
                                     summon_any_demon(DEMON_COMMON));
         const bool good_summon =
@@ -427,13 +424,13 @@ static bool evoke_sceptre_of_asmodeus()
     return (true);
 }
 
-// returns true if item successfully evoked.
+// Returns true if item successfully evoked.
 bool evoke_wielded()
 {
     int power = 0;
 
-    int pract = 0;
-    bool did_work = false;  // used for default "nothing happens" message
+    int pract = 0; // By how much Evocations is practised.
+    bool did_work = false;  // Used for default "nothing happens" message.
 
     const int wield = you.equip[EQ_WEAPON];
 
@@ -493,7 +490,7 @@ bool evoke_wielded()
                 break;
 
             case SPWPN_SCEPTRE_OF_ASMODEUS:
-                if ( evoke_sceptre_of_asmodeus() )
+                if (evoke_sceptre_of_asmodeus())
                 {
                     make_hungry(200, false, true);
                     did_work = true;
@@ -597,7 +594,7 @@ bool evoke_wielded()
     case OBJ_MISCELLANY:
         did_work = true; // easier to do it this way for misc items
 
-        if ( is_deck(wpn) )
+        if (is_deck(wpn))
         {
             evoke_deck(wpn);
             pract = 1;
@@ -647,7 +644,7 @@ bool evoke_wielded()
             break;
 
         case MISC_HORN_OF_GERYON:
-            if ( evoke_horn_of_geryon() )
+            if (evoke_horn_of_geryon())
                 pract = 1;
             break;
 
@@ -735,8 +732,8 @@ static bool ball_of_seeing(void)
 
     mpr("You gaze into the crystal ball.");
 
-    use = ((!you.duration[DUR_CONF]) ?
-           random2(you.skills[SK_EVOCATIONS] * 6) : random2(5));
+    use = (!you.duration[DUR_CONF] ? random2(you.skills[SK_EVOCATIONS] * 6)
+                                   : random2(5));
 
     if (use < 2)
     {
@@ -778,11 +775,11 @@ static bool disc_of_storms(void)
     const int fail_rate = (30 - you.skills[SK_EVOCATIONS]);
     bool ret = false;
 
-    if (player_res_electricity() || (random2(100) < fail_rate))
+    if (player_res_electricity() || x_chance_in_y(fail_rate, 100))
         canned_msg(MSG_NOTHING_HAPPENS);
-    else if (random2(100) < fail_rate)
+    else if (x_chance_in_y(fail_rate, 100))
         mpr("The disc glows for a moment, then fades.");
-    else if (random2(100) < fail_rate)
+    else if (x_chance_in_y(fail_rate, 100))
         mpr("Little bolts of electricity crackle over the disc.");
     else
     {
@@ -805,7 +802,7 @@ static bool disc_of_storms(void)
             beam.target_x = you.x_pos + random2(13) - 6;
             beam.target_y = you.y_pos + random2(13) - 6;
 
-            // non-controlleable
+            // Non-controlleable, so no player tracer.
             zapping( which_zap, 30 + you.skills[SK_EVOCATIONS] * 2, beam );
 
             disc_count--;
@@ -815,7 +812,7 @@ static bool disc_of_storms(void)
     }
 
     return (ret);
-}                               // end disc_of_storms()
+}
 
 void tome_of_power(int slot)
 {
@@ -833,7 +830,7 @@ void tome_of_power(int slot)
     set_ident_flags( you.inv[slot], ISFLAG_KNOW_TYPE );
 
     if (player_mutation_level(MUT_BLURRY_VISION) > 0
-        && random2(4) < player_mutation_level(MUT_BLURRY_VISION))
+        && x_chance_in_y(player_mutation_level(MUT_BLURRY_VISION), 4))
     {
         mpr("The page is too blurry for you to read.");
         return;
@@ -842,27 +839,27 @@ void tome_of_power(int slot)
     mpr("You find yourself reciting the magical words!");
     exercise( SK_EVOCATIONS, 1 );
 
-    if ( random2(50) < 7 )
+    if (x_chance_in_y(7, 50))
     {
         mpr("A cloud of weird smoke pours from the book's pages!");
         big_cloud( random_smoke_type(), KC_YOU,
                    you.x_pos, you.y_pos, 20, 10 + random2(8) );
         xom_is_stimulated(16);
     }
-    else if ( random2(43) < 2 )
+    else if (x_chance_in_y(2, 43))
     {
         mpr("A cloud of choking fumes pours from the book's pages!");
         big_cloud(CLOUD_POISON, KC_YOU,
                   you.x_pos, you.y_pos, 20, 7 + random2(5));
         xom_is_stimulated(64);
     }
-    else if ( random2(41) < 2 )
+    else if (x_chance_in_y(2, 41))
     {
         mpr("A cloud of freezing gas pours from the book's pages!");
         big_cloud(CLOUD_COLD, KC_YOU, you.x_pos, you.y_pos, 20, 8 + random2(5));
         xom_is_stimulated(64);
     }
-    else if ( random2(39) < 3 )
+    else if (x_chance_in_y(3, 39))
     {
         if (one_chance_in(5))
         {
@@ -1035,7 +1032,7 @@ static bool ball_of_energy(void)
     {
         lose_stat(STAT_INTELLIGENCE, 1, false, "using a ball of energy");
     }
-    else if ((use < 4 && enough_mp(1, true))
+    else if (use < 4 && enough_mp(1, true)
              || you.magic_points == you.max_magic_points)
     {
         mpr( "You feel your power drain away!" );
diff --git a/crawl-ref/source/item_use.cc b/crawl-ref/source/item_use.cc
index 49855a0b41..568645fc89 100644
--- a/crawl-ref/source/item_use.cc
+++ b/crawl-ref/source/item_use.cc
@@ -135,8 +135,7 @@ bool can_wield(const item_def *weapon, bool say_reason,
     if (weapon->base_type != OBJ_WEAPONS)
         return (true);
 
-    if ((you.species < SP_OGRE || you.species > SP_OGRE_MAGE)
-            && item_mass( *weapon ) >= 300)
+    if (player_size(PSIZE_TORSO) < SIZE_LARGE && item_mass( *weapon ) >= 300)
     {
         SAY(mpr("That's too large and heavy for you to wield."));
         return (false);
@@ -164,8 +163,7 @@ bool can_wield(const item_def *weapon, bool say_reason,
 
     int weap_brand = get_weapon_brand( *weapon );
     if ((you.is_undead || you.species == SP_DEMONSPAWN)
-        && (weap_brand == SPWPN_HOLY_WRATH
-            || is_blessed_blade(*weapon)))
+        && (weap_brand == SPWPN_HOLY_WRATH || is_blessed_blade(*weapon)))
     {
         SAY(mpr("This weapon will not allow you to wield it."));
         return (false);
@@ -376,10 +374,12 @@ static void warn_rod_shield_interference(const item_def &)
 
     // Any way to avoid the double entendre? :-)
     if (leak_degree)
+    {
         mprf(MSGCH_WARN,
                 "Your %s %sreduces the effectiveness of your rod.",
                 shield_base_name(player_shield()),
                 leak_degree);
+    }
 }
 
 static void warn_launcher_shield_slowdown(const item_def &launcher)
@@ -394,11 +394,14 @@ static void warn_launcher_shield_slowdown(const item_def &launcher)
     {
         const char *slow_degree =
             shield_impact_degree(slowspeed * 100 / normspeed);
+
         if (slow_degree)
+        {
             mprf(MSGCH_WARN,
                     "Your %s %sslows your rate of fire.",
                     shield_base_name(player_shield()),
                     slow_degree);
+        }
     }
 }
 
@@ -4285,7 +4288,7 @@ void read_scroll( int slot )
 
     // Imperfect vision prevents players from reading actual content {dlb}:
     if (player_mutation_level(MUT_BLURRY_VISION)
-        && random2(5) < player_mutation_level(MUT_BLURRY_VISION))
+        && x_chance_in_y(player_mutation_level(MUT_BLURRY_VISION), 5))
     {
         mpr((player_mutation_level(MUT_BLURRY_VISION) == 3 && one_chance_in(3))
                         ? "This scroll appears to be blank."
diff --git a/crawl-ref/source/maps.cc b/crawl-ref/source/maps.cc
index 426136969b..1eb3685d0a 100644
--- a/crawl-ref/source/maps.cc
+++ b/crawl-ref/source/maps.cc
@@ -376,7 +376,7 @@ int random_map_for_place(const level_id &place, bool want_minivault)
         {
             rollsize += vdefs[i].chance;
 
-            if (rollsize && random2(rollsize) < vdefs[i].chance)
+            if (rollsize && x_chance_in_y(vdefs[i].chance, rollsize))
                 mapindex = i;
         }
     }
@@ -417,7 +417,7 @@ int random_map_in_depth(const level_id &place, bool want_minivault)
         {
             rollsize += vdefs[i].chance;
 
-            if (rollsize && random2(rollsize) < vdefs[i].chance)
+            if (rollsize && x_chance_in_y(vdefs[i].chance, rollsize))
                 mapindex = i;
         }
 
@@ -444,7 +444,7 @@ int random_map_for_tag(const std::string &tag,
         {
             rollsize += vdefs[i].chance;
 
-            if (rollsize && random2(rollsize) < vdefs[i].chance)
+            if (rollsize && x_chance_in_y(vdefs[i].chance, rollsize))
                 mapindex = i;
         }
     }
diff --git a/crawl-ref/source/mgrow.cc b/crawl-ref/source/mgrow.cc
index bdaf066465..40025ee814 100644
--- a/crawl-ref/source/mgrow.cc
+++ b/crawl-ref/source/mgrow.cc
@@ -89,7 +89,7 @@ static const monster_level_up *_monster_level_up_target( monster_type type,
         {
             const monsterentry *me = get_monster_data(mlup.after);
             if (static_cast<int>(me->hpdice[0]) == hit_dice
-                && random2(1000) < mlup.chance)
+                && x_chance_in_y(mlup.chance, 1000))
             {
                 return (&mlup);
             }
diff --git a/crawl-ref/source/monplace.cc b/crawl-ref/source/monplace.cc
index c03517a98d..4d6a8b2ba7 100644
--- a/crawl-ref/source/monplace.cc
+++ b/crawl-ref/source/monplace.cc
@@ -205,7 +205,7 @@ static void _hell_spawn_random_monsters()
     if (env.turns_on_level > taper_off_turn)
     {
         genodds += (env.turns_on_level - taper_off_turn);
-        genodds = (genodds < 0 ? 20000 : std::min(genodds, 20000));
+        genodds  = (genodds < 0 ? 20000 : std::min(genodds, 20000));
     }
 
     if (one_chance_in(genodds))
@@ -538,7 +538,7 @@ static int _is_near_stairs(coord_def &p)
     return (result);
 }
 
-static bool _valid_monster_location(const mgen_data &mg, 
+static bool _valid_monster_location(const mgen_data &mg,
                                     const coord_def &mg_pos)
 {
     const int htype = (mons_class_is_zombified(mg.cls) ? mg.base_type
diff --git a/crawl-ref/source/mstuff2.cc b/crawl-ref/source/mstuff2.cc
index 9bf6cde740..cc0303ea60 100644
--- a/crawl-ref/source/mstuff2.cc
+++ b/crawl-ref/source/mstuff2.cc
@@ -187,7 +187,8 @@ void mons_trap(monsters *monster)
         }
 
         if (random2(monster->ev) > 8
-            || trapKnown && intelligent_ally(monster) && random2(monster->ev) > 8)
+            || trapKnown && intelligent_ally(monster)
+               && random2(monster->ev) > 8)
         {
             if (monsterNearby && !simple_monster_message(monster,
                                            " avoids a huge, swinging blade."))
@@ -241,7 +242,8 @@ void mons_trap(monsters *monster)
         }
 
         if (random2(monster->ev) > 8
-            || trapKnown && intelligent_ally(monster) && random2(monster->ev) > 8)
+            || trapKnown && intelligent_ally(monster)
+               && random2(monster->ev) > 8)
         {
             if (monsterNearby && !simple_monster_message(monster,
                                  " nimbly jumps out of the way of a falling net."))
@@ -287,6 +289,7 @@ void mons_trap(monsters *monster)
                 mpr("The power of Zot is invoked against you!");
                 miscast_effect( SPTYP_RANDOM, 10 + random2(30),
                                 75 + random2(100), 0, "the power of Zot" );
+
                 return;         // early return {dlb}
             }
         }
@@ -301,8 +304,8 @@ void mons_trap(monsters *monster)
                 mpr("You hear a distant \"Zot\"!", MSGCH_SOUND);
         }
 
-        // determine trap effects upon monster, based upon
-        // whether it is naughty or nice to the player: {dlb}
+        // Determine trap effects upon monster, based upon
+        // whether it is naughty or nice to the player. {dlb}
 
         // NB: beem[].colour values are mislabeled as colours (?) -
         //     cf. mons_ench_f2() [which are also mislabeled] {dlb}
@@ -378,7 +381,7 @@ void mons_trap(monsters *monster)
 
             if (beem.colour == OBJ_MISSILES
                 && beem.type == MI_NEEDLE
-                && random2(100) < 50 - (3*monster->ac/2))
+                && x_chance_in_y(50 - (3 * monster->ac)/ 2, 100))
             {
                 apply_poison = true;
             }
@@ -400,8 +403,8 @@ void mons_trap(monsters *monster)
         if (apply_poison)
             poison_monster( monster, KC_OTHER );
 
-        // generate "fallen" projectile, where appropriate: {dlb}
-        if (random2(10) < 7)
+        // Generate "fallen" projectile, where appropriate. {dlb}
+        if (x_chance_in_y(7, 10))
         {
             beem.target_x = monster->x;
             beem.target_y = monster->y;
diff --git a/crawl-ref/source/mutation.cc b/crawl-ref/source/mutation.cc
index af0d204581..ff05e986dd 100644
--- a/crawl-ref/source/mutation.cc
+++ b/crawl-ref/source/mutation.cc
@@ -1633,8 +1633,9 @@ static bool accept_mutation(mutation_type mutat, bool ignore_rarity = false)
         return (true);
 
     const int rarity = mutation_defs[mutat].rarity + you.demon_pow[mutat];
+
     // Low rarity means unlikely to choose it.
-    return (rarity > random2(10));
+    return (x_chance_in_y(rarity, 10));
 }
 
 static mutation_type get_random_xom_mutation()
@@ -1687,7 +1688,7 @@ static mutation_type get_random_mutation(bool prefer_good,
 
         cweight += weight;
 
-        if (random2(cweight) < weight)
+        if (x_chance_in_y(weight, cweight))
             chosen = curr;
     }
     return (chosen);
@@ -1718,7 +1719,7 @@ bool mutate(mutation_type which_mutation, bool failMsg,
         }
 
         // Zin's protection.
-        if (you.religion == GOD_ZIN && you.piety > random2(MAX_PIETY))
+        if (you.religion == GOD_ZIN && x_chance_in_y(you.piety, MAX_PIETY))
         {
             simple_god_message(" protects your body from chaos!");
             return (false);
@@ -1781,7 +1782,8 @@ bool mutate(mutation_type which_mutation, bool failMsg,
     if (which_mutation == RANDOM_MUTATION
         || which_mutation == RANDOM_XOM_MUTATION)
     {
-        if (random2(15) < how_mutated(false, true))
+        // If already heavily mutated, remove a mutation instead.
+        if (x_chance_in_y(how_mutated(false, true), 15))
         {
             // God gifts override mutation loss due to being heavily
             // mutated.
diff --git a/crawl-ref/source/ouch.cc b/crawl-ref/source/ouch.cc
index 4ff2e61713..e60da7c57b 100644
--- a/crawl-ref/source/ouch.cc
+++ b/crawl-ref/source/ouch.cc
@@ -233,7 +233,7 @@ int check_your_resists(int hurted, beam_type flavour)
         break;
 
     case BEAM_MIASMA:
-        if (player_prot_life() > random2(3))
+        if (x_chance_in_y(player_prot_life(), 3))
         {
             canned_msg(MSG_YOU_RESIST);
             hurted = 0;
@@ -398,8 +398,8 @@ void item_corrode( int itco )
         // {dlb}
         if (chance_corr >= 0 && chance_corr <= 4)
         {
-            it_resists = (random2(100) <
-                            2 + (4 << chance_corr) + (chance_corr * 8));
+            it_resists
+               = x_chance_in_y(2 + (4 << chance_corr) + chance_corr * 8, 100);
         }
         else
             it_resists = true;  // no idea how often this occurs {dlb}
@@ -497,7 +497,7 @@ static void _expose_invent_to_element(beam_type flavour, int strength)
 
             for (int j = 0; j < you.inv[i].quantity; ++j)
             {
-                if (random2(100) < strength)
+                if (x_chance_in_y(strength, 100))
                 {
                     num_dest++;
 
diff --git a/crawl-ref/source/player.cc b/crawl-ref/source/player.cc
index 3057aedbbf..4ded8c08f8 100644
--- a/crawl-ref/source/player.cc
+++ b/crawl-ref/source/player.cc
@@ -5954,10 +5954,10 @@ bool player::alive() const
 
 bool player::fumbles_attack(bool verbose)
 {
-    // fumbling in shallow water <early return>:
+    // Fumbling in shallow water.
     if (floundering())
     {
-        if (random2(dex) < 4 || one_chance_in(5))
+        if (x_chance_in_y(4, dex) || one_chance_in(5))
         {
             if (verbose)
                 mpr("Unstable footing causes you to fumble your attack.");
@@ -6008,9 +6008,9 @@ void player::attacking(actor *other)
             pet_target = monster_index(mon);
     }
 
-    if (mutation[MUT_BERSERK]
-        && (random2(100) < (mutation[MUT_BERSERK] * 10) - 5)
-            || _equipment_make_berserk())
+    if (player_mutation_level(MUT_BERSERK)
+            && x_chance_in_y(player_mutation_level(MUT_BERSERK) * 10 - 5, 100)
+        || _equipment_make_berserk())
     {
         go_berserk(false);
     }
diff --git a/crawl-ref/source/randart.cc b/crawl-ref/source/randart.cc
index 15396bfd7c..63a85194a6 100644
--- a/crawl-ref/source/randart.cc
+++ b/crawl-ref/source/randart.cc
@@ -194,7 +194,7 @@ static std::string _replace_name_parts(const std::string name_in,
         std::string place;
         if (one_chance_in(5))
         {
-            switch(random2(8))
+            switch (random2(8))
             {
             case 0:
             case 1:
@@ -804,7 +804,7 @@ void static _get_randart_properties(const item_def &item,
     if (random2(15) >= power_level && aclass != OBJ_WEAPONS
         && (aclass != OBJ_JEWELLERY || atype != RING_SLAYING))
     {
-        // Weapons and rings of slaying can't get these
+        // Weapons and rings of slaying can't get these.
         if (one_chance_in(4 + power_level))  // to-hit
         {
             proprt[RAP_ACCURACY] = 1 + random2(3) + random2(2);
@@ -867,7 +867,7 @@ void static _get_randart_properties(const item_def &item,
         power_level++;
     }
 
-    if (random2(12) < power_level || power_level > 7)
+    if (x_chance_in_y(power_level, 12) || power_level > 7)
         done_powers = true;
 
     // res_elec
@@ -923,7 +923,7 @@ void static _get_randart_properties(const item_def &item,
         power_level++;
     }
 
-    if (random2(12) < power_level || power_level > 10)
+    if (x_chance_in_y(power_level, 12) || power_level > 10)
         done_powers = true;
 
     // turn invis
@@ -981,7 +981,7 @@ void static _get_randart_properties(const item_def &item,
     if (aclass == OBJ_ARMOUR)
         power_level -= 4;
 
-    if (power_level >= 2 && random2(17) < power_level)
+    if (power_level >= 2 && x_chance_in_y(power_level, 17))
     {
         switch (random2(9))
         {
@@ -1488,8 +1488,8 @@ bool make_item_fixed_artefact( item_def &item, bool in_abyss, int which )
 
     if (!force)
     {
-        which = SPWPN_START_FIXEDARTS +
-            random2(SPWPN_START_NOGEN_FIXEDARTS - SPWPN_START_FIXEDARTS);
+        which = SPWPN_START_FIXEDARTS
+                + random2(SPWPN_START_NOGEN_FIXEDARTS - SPWPN_START_FIXEDARTS);
     }
 
     const unique_item_status_type status =
diff --git a/crawl-ref/source/religion.cc b/crawl-ref/source/religion.cc
index 28861f3f46..094dc87a02 100644
--- a/crawl-ref/source/religion.cc
+++ b/crawl-ref/source/religion.cc
@@ -2652,7 +2652,7 @@ bool did_god_conduct(conduct_type thing_done, int level, bool known,
             // use up the deck, and 80% on a card which does use up the
             // deck.
             int chance = 0;
-            switch(level)
+            switch (level)
             {
             case 0: chance = 0;   break;
             case 1: chance = 40;  break;
@@ -2661,7 +2661,8 @@ bool did_god_conduct(conduct_type thing_done, int level, bool known,
             case 3: chance = 100; break;
             }
 
-            if (random2(100) < chance && you.attribute[ATTR_CARD_COUNTDOWN])
+            if (x_chance_in_y(chance, 100)
+                && you.attribute[ATTR_CARD_COUNTDOWN])
             {
                 you.attribute[ATTR_CARD_COUNTDOWN]--;
 #if DEBUG_DIAGNOSTICS || DEBUG_CARDS || DEBUG_GIFTS
@@ -3446,10 +3447,11 @@ static bool _zin_retribution()
     int punishment = random2(10);
 
     // if little mutated or can't unmutate, do something else instead
-    if (punishment < 2 && (how_mutated() <= random2(3)
-        || player_mutation_level(MUT_MUTATION_RESISTANCE) == 3))
+    if (punishment < 2
+        && (how_mutated() <= random2(3)
+            || player_mutation_level(MUT_MUTATION_RESISTANCE) == 3))
     {
-        punishment = random2(8)+2;
+        punishment = random2(8) + 2;
     }
 
     switch (punishment)
@@ -3460,16 +3462,13 @@ static bool _zin_retribution()
         simple_god_message(" draws some chaos from your body!", god);
         bool success = false;
         for (int i = 0; i < 7; ++i)
-            if (random2(10) > i
-                && delete_mutation(RANDOM_GOOD_MUTATION))
-            {
+            if (x_chance_in_y(i, 10) && delete_mutation(RANDOM_GOOD_MUTATION))
                 success = true;
-            }
 
         if (success && !how_mutated())
         {
             simple_god_message(" rids your body of chaos!", god);
-            // lower penance a bit more for being particularly successful
+            // Lower penance a bit more for being particularly successful.
             dec_penance(god, 1);
         }
         break;
diff --git a/crawl-ref/source/spells1.cc b/crawl-ref/source/spells1.cc
index 9df1997998..6c8be52d3c 100644
--- a/crawl-ref/source/spells1.cc
+++ b/crawl-ref/source/spells1.cc
@@ -1181,10 +1181,8 @@ bool cast_revivification(int pow)
 
         loss = 2;
         for (loopy = 0; loopy < 9; loopy++)
-        {
-            if (random2(pow) < 8)
+            if (x_chance_in_y(8, pow))
                 loss++;
-        }
 
         dec_max_hp(loss);
         set_hp(you.hp_max, false);
@@ -1242,7 +1240,8 @@ void cast_deaths_door(int pow)
         set_hp( allowed_deaths_door_hp(), false );
         deflate_hp( you.hp_max, false );
 
-        you.duration[DUR_DEATHS_DOOR] = 10 + random2avg(13, 3) + (random2(pow) / 10);
+        you.duration[DUR_DEATHS_DOOR] = 10 + random2avg(13, 3)
+                                           + (random2(pow) / 10);
 
         if (you.duration[DUR_DEATHS_DOOR] > 25)
             you.duration[DUR_DEATHS_DOOR] = 23 + random2(5);
@@ -1334,7 +1333,7 @@ void antimagic()
         if ( you.duration[dur_list[i]] > 1 )
             you.duration[dur_list[i]] = 1;
 
-    contaminate_player( -1 * (1+random2(5)));
+    contaminate_player( -1 * (1 + random2(5)));
 }                               // end antimagic()
 
 void extension(int pow)
@@ -1691,7 +1690,7 @@ bool cast_sure_blade(int power)
     }
 
     return (success);
-}                               // end cast_sure_blade()
+}
 
 void manage_fire_shield(void)
 {
@@ -1703,7 +1702,6 @@ void manage_fire_shield(void)
     char stx = 0, sty = 0;
 
     for (stx = -1; stx < 2; stx++)
-    {
         for (sty = -1; sty < 2; sty++)
         {
             if (sty == 0 && stx == 0)
@@ -1718,5 +1716,4 @@ void manage_fire_shield(void)
                              1 + random2(6), KC_YOU );
             }
         }
-    }
-}                               // end manage_fire_shield()
+}
diff --git a/crawl-ref/source/spells2.cc b/crawl-ref/source/spells2.cc
index 797e233c43..3955799d24 100644
--- a/crawl-ref/source/spells2.cc
+++ b/crawl-ref/source/spells2.cc
@@ -159,7 +159,7 @@ static bool _mark_detected_creature(int gridx, int gridy, const monsters *mon,
 
     bool found_good = false;
 
-    if (fuzz_radius && fuzz_chance > random2(100))
+    if (fuzz_radius && x_chance_in_y(fuzz_chance, 100))
     {
         const int fuzz_diam = 2 * fuzz_radius + 1;
 
@@ -1154,7 +1154,8 @@ bool cast_sticks_to_snakes(int pow, god_type god)
             if (one_chance_in(5 - std::min(4, div_rand_round(pow * 2, 25)))
                 || get_ammo_brand(you.inv[wpn]) == SPMSL_POISONED)
             {
-                mon = random2(100) < pow / 3 ? MONS_BROWN_SNAKE : MONS_SNAKE;
+                mon = x_chance_in_y(pow / 3, 100) ? MONS_BROWN_SNAKE
+                                                  : MONS_SNAKE;
             }
             else
                 mon = MONS_SMALL_SNAKE;
@@ -1518,17 +1519,18 @@ bool cast_summon_elemental(int pow, god_type god,
     // - Earth elementals are more static and easy to tame (as before).
     // - Fire elementals fall in between the two (10 is still fairly easy).
     const bool friendly = ((mon != MONS_FIRE_ELEMENTAL
-                            || random2(10) < you.skills[SK_FIRE_MAGIC])
+                            || x_chance_in_y(you.skills[SK_FIRE_MAGIC], 10))
 
                         && (mon != MONS_WATER_ELEMENTAL
-                            || random2((you.species == SP_MERFOLK) ? 5 : 15)
-                                  < you.skills[SK_ICE_MAGIC])
+                            || x_chance_in_y(you.skills[SK_ICE_MAGIC],
+                                             (you.species == SP_MERFOLK) ? 5
+                                                                         : 15))
 
                         && (mon != MONS_AIR_ELEMENTAL
-                            || random2(15) < you.skills[SK_AIR_MAGIC])
+                            || x_chance_in_y(you.skills[SK_AIR_MAGIC], 15))
 
                         && (mon != MONS_EARTH_ELEMENTAL
-                            || random2(5)  < you.skills[SK_EARTH_MAGIC])
+                            || x_chance_in_y(you.skills[SK_EARTH_MAGIC], 5))
 
                         && random2(100) >= unfriendly);
 
diff --git a/crawl-ref/source/spells3.cc b/crawl-ref/source/spells3.cc
index d866db7181..aabfc95a42 100644
--- a/crawl-ref/source/spells3.cc
+++ b/crawl-ref/source/spells3.cc
@@ -97,10 +97,9 @@ bool cast_selective_amnesia(bool force)
             mpr( "You don't know that spell." );
         else
         {
-            if (!force
-                 && (you.religion != GOD_SIF_MUNA
-                     && random2(you.skills[SK_SPELLCASTING])
-                         < random2(spell_difficulty( spell ))))
+            if (!force && you.religion != GOD_SIF_MUNA
+                && random2(you.skills[SK_SPELLCASTING])
+                    < random2(spell_difficulty( spell )))
             {
                 mpr("Oops! This spell sure is a blunt instrument.");
                 forget_map(20 + random2(50));
@@ -397,12 +396,10 @@ bool cast_sublimation_of_blood(int pow)
                     food += 15;
 
                 for (int loopy = 0; loopy < (you.hp > 1 ? 3 : 0); ++loopy)
-                {
-                    if (random2(pow) < 6)
+                    if (x_chance_in_y(6, pow))
                         dec_hp(1, false);
-                }
 
-                if (random2(pow) < 6)
+                if (x_chance_in_y(6, pow))
                     break;
             }
 
@@ -1196,9 +1193,9 @@ bool cast_summon_wraiths(int pow, god_type god)
         canned_msg(MSG_NOTHING_HAPPENS);
 
     //jmf: Kiku sometimes deflects this
-    if (!(you.religion == GOD_KIKUBAAQUDGHA
-           && (!player_under_penance() && you.piety >= piety_breakpoint(3)
-           && you.piety > random2(MAX_PIETY))))
+    if (you.religion != GOD_KIKUBAAQUDGHA
+        || player_under_penance() || you.piety < piety_breakpoint(3)
+        || !x_chance_in_y(you.piety, MAX_PIETY))
     {
         disease_player(25 + random2(50));
     }
diff --git a/crawl-ref/source/spells4.cc b/crawl-ref/source/spells4.cc
index 4384a84ced..5d62772b28 100644
--- a/crawl-ref/source/spells4.cc
+++ b/crawl-ref/source/spells4.cc
@@ -291,7 +291,7 @@ static int _shatter_walls(int x, int y, int pow, int garbage)
         break;
     }
 
-    if (random2(100) < chance)
+    if (x_chance_in_y(chance, 100))
     {
         noisy(30, x, y);
 
@@ -1699,7 +1699,7 @@ void do_monster_rot(int mon)
 {
     int damage = 1 + random2(3);
 
-    if (mons_holiness(&menv[mon]) == MH_UNDEAD && random2(5))
+    if (mons_holiness(&menv[mon]) == MH_UNDEAD && !one_chance_in(5))
     {
         apply_area_cloud(make_a_normal_cloud, menv[mon].x, menv[mon].y,
                          10, 1, CLOUD_MIASMA, KC_YOU);
@@ -1815,7 +1815,7 @@ void cast_fragmentation(int pow)        // jmf: ripped idea from airstrike
 
             blast.colour = LIGHTGREY;
 
-            if (random2(50) < (pow / 5))        // potential insta-kill
+            if (x_chance_in_y(pow / 5, 50))        // potential insta-kill
             {
                 monster_die(&menv[mon], KILL_YOU, 0);
                 blast.damage.num = 4;
diff --git a/crawl-ref/source/spl-cast.cc b/crawl-ref/source/spl-cast.cc
index 42d8de5c5f..08e9890a99 100644
--- a/crawl-ref/source/spl-cast.cc
+++ b/crawl-ref/source/spl-cast.cc
@@ -795,7 +795,7 @@ bool maybe_identify_staff(item_def &item, spell_type spell)
         if (you.skills[SK_SPELLCASTING] > relevant_skill)
             relevant_skill = you.skills[SK_SPELLCASTING];
 
-        if (random2(100) < relevant_skill)
+        if (x_chance_in_y(relevant_skill, 100))
             id_staff = true;
     }
     else if (relevant_skill >= 4)
diff --git a/crawl-ref/source/spl-util.cc b/crawl-ref/source/spl-util.cc
index 364ab2461a..6edc0d33a8 100644
--- a/crawl-ref/source/spl-util.cc
+++ b/crawl-ref/source/spl-util.cc
@@ -330,10 +330,8 @@ int count_bits(unsigned int bits)
     int c = 0;
 
     for (n = 1; n < INT_MAX; n <<= 1)
-    {
         if (n & bits)
             c++;
-    }
 
     return (c);
 }
@@ -370,7 +368,7 @@ int apply_area_visible( int (*func) (int, int, int, int), int power,
     }
 
     return (rv);
-}                               // end apply_area_visible()
+}
 
 // Applies the effect to all nine squares around/including the target.
 // Returns summation of return values from passed in function.
@@ -381,15 +379,11 @@ int apply_area_square( int (*func) (int, int, int, int), int cx, int cy,
     int rv = 0;
 
     for (x = cx - 1; x <= cx + 1; x++)
-    {
         for (y = cy - 1; y <= cy + 1; y++)
-        {
             rv += func(x, y, power, 0);
-        }
-    }
 
     return (rv);
-}                               // end apply_area_square()
+}
 
 
 // Applies the effect to the eight squares beside the target.
@@ -401,7 +395,6 @@ int apply_area_around_square( int (*func) (int, int, int, int),
     int rv = 0;
 
     for (x = targ_x - 1; x <= targ_x + 1; x++)
-    {
         for (y = targ_y - 1; y <= targ_y + 1; y++)
         {
             if (x == targ_x && y == targ_y)
@@ -409,9 +402,9 @@ int apply_area_around_square( int (*func) (int, int, int, int),
             else
                 rv += func(x, y, power, 0);
         }
-    }
+
     return (rv);
-}                               // end apply_area_around_square()
+}
 
 // Effect up to max_targs monsters around a point, chosen randomly
 // Return varies with the function called;  return values will be added up.
@@ -425,14 +418,10 @@ int apply_random_around_square( int (*func) (int, int, int, int),
         return 0;
 
     if (max_targs >= 9 && !hole_in_middle)
-    {
         return (apply_area_square( func, targ_x, targ_y, power ));
-    }
 
     if (max_targs >= 8 && hole_in_middle)
-    {
         return (apply_area_around_square( func, targ_x, targ_y, power ));
-    }
 
     FixedVector< coord_def, 8 > targs;
     int count = 0;
@@ -525,7 +514,7 @@ int apply_random_around_square( int (*func) (int, int, int, int),
                 targs[ count - 1 ].x = x;
                 targs[ count - 1 ].y = y;
             }
-            else if (random2( count ) < max_targs)
+            else if (x_chance_in_y(max_targs, count))
             {
                 const int pick = random2( max_targs );
                 targs[ pick ].x = x;
diff --git a/crawl-ref/source/stuff.cc b/crawl-ref/source/stuff.cc
index 159b09ae48..6fef267f58 100644
--- a/crawl-ref/source/stuff.cc
+++ b/crawl-ref/source/stuff.cc
@@ -866,30 +866,41 @@ bool one_chance_in(int a_million)
     return (random2(a_million) == 0);
 }
 
-// simple little function to quickly modify all three stats
+bool x_chance_in_y(int x, int y)
+{
+    if (x <= 0 || y <= 0)
+        return (false);
+
+    if (x >= y)
+        return (true);
+
+    return (random2(y) < x);
+}
+
+// Simple little function to quickly modify all three stats
 // at once - does check for '0' modifiers to prevent needless
 // adding .. could use checking for sums less than zero, I guess.
-// used in conjunction with newgame::species_stat_init() and
-// newgame::job_stat_init() routines 24jan2000 {dlb}
+// Used in conjunction with newgame::species_stat_init() and
+// newgame::job_stat_init() routines 24jan2000. {dlb}
 void modify_all_stats(int STmod, int IQmod, int DXmod)
 {
     if (STmod)
     {
-        you.strength += STmod;
+        you.strength     += STmod;
         you.max_strength += STmod;
         you.redraw_strength = true;
     }
 
     if (IQmod)
     {
-        you.intel += IQmod;
+        you.intel     += IQmod;
         you.max_intel += IQmod;
         you.redraw_intelligence = true;
     }
 
     if (DXmod)
     {
-        you.dex += DXmod;
+        you.dex     += DXmod;
         you.max_dex += DXmod;
         you.redraw_dexterity = true;
     }
diff --git a/crawl-ref/source/stuff.h b/crawl-ref/source/stuff.h
index 2883e3cacf..60c2ae4305 100644
--- a/crawl-ref/source/stuff.h
+++ b/crawl-ref/source/stuff.h
@@ -34,6 +34,7 @@ bool coinflip();
 int div_rand_round( int num, int den );
 int div_round_up( int num, int den );
 bool one_chance_in(int a_million);
+bool x_chance_in_y(int x, int y);
 int random2(int randmax);
 int random_range(int low, int high);
 int random_range(int low, int high, int nrolls);
diff --git a/crawl-ref/source/xom.cc b/crawl-ref/source/xom.cc
index fc40cb3750..6af82176bb 100644
--- a/crawl-ref/source/xom.cc
+++ b/crawl-ref/source/xom.cc
@@ -227,17 +227,17 @@ static object_class_type _get_unrelated_wield_class(object_class_type ref)
     object_class_type objtype = OBJ_WEAPONS;
     if (ref == OBJ_WEAPONS)
     {
-        if (random2(10))
-            objtype = OBJ_STAVES;
-        else
+        if (one_chance_in(10))
             objtype = OBJ_MISCELLANY;
+        else
+            objtype = OBJ_STAVES;
     }
     else if (ref == OBJ_STAVES)
     {
-        if (random2(10))
-            objtype = OBJ_WEAPONS;
-        else
+        if (one_chance_in(10))
             objtype = OBJ_MISCELLANY;
+        else
+            objtype = OBJ_WEAPONS;
     }
     else
     {
@@ -313,7 +313,7 @@ static bool _xom_annoyance_gift(int power)
             const object_class_type objtype =
                 _get_unrelated_wield_class(weapon->base_type);
 
-            if (power > random2(256))
+            if (x_chance_in_y(power, 256))
                 acquirement(objtype, GOD_XOM);
             else
                 _xom_make_item(objtype, OBJ_RANDOM, power * 3);
@@ -336,9 +336,8 @@ static bool _xom_gives_item(int power)
         // cloak or body armour.  Ha ha!
         god_speaks(GOD_XOM, _get_xom_speech("armour gift").c_str());
         _xom_make_item(OBJ_ARMOUR,
-                       random2(10) ?
-                           get_random_body_armour_type(you.your_level * 2)
-                       : ARM_CLOAK,
+                       one_chance_in(10) ? ARM_CLOAK :
+                                get_random_body_armour_type(you.your_level * 2),
                        power * 3);
         return (true);
     }
@@ -350,7 +349,7 @@ static bool _xom_gives_item(int power)
     // better than random object), and it is sometimes tuned to the
     // player's skills and nature.  Being tuned to the player's skills
     // and nature is not very Xomlike...
-    if (power > random2(256))
+    if (x_chance_in_y(power, 256))
     {
         // Random-type acquirement.
         const int r = random2(7);
@@ -465,6 +464,7 @@ static bool _xom_is_good(int sever)
     }
     else if (random2(sever) <= 3)
     {
+        // XXX: Can we clean up this ugliness, please?
         const int numdemons =
             std::min(random2(random2(random2(sever+1)+1)+1)+2, 16);
         int numdifferent = 0;