3 files changed, 82 insertions, 5 deletions
diff --git a/crawl-ref/source/rng.cc b/crawl-ref/source/rng.cc
index 8c856e7229..4b7200093c 100644
--- a/crawl-ref/source/rng.cc
+++ b/crawl-ref/source/rng.cc
@@ -29,6 +29,12 @@ void seed_rng(unsigned long* seed_key, size_t num_keys)
     // MT19937 -- see mt19937ar.cc for details/licence
     init_by_array(seed_key, num_keys);
 
+    // Reset the sha256 generator to get predictable random numbers in case
+    // of a saved rng state.
+#ifdef MORE_HARDENED_PRNG
+    reset_sha256_state();
+#endif
+
     // for std::random_shuffle()
     srand(seed_key[0]);
 }
@@ -38,6 +44,12 @@ void seed_rng(long seed)
     // MT19937 -- see mt19937ar.cc for details/licence
     init_genrand(seed);
 
+    // Reset the sha256 generator to get predictable random numbers in case
+    // of a saved rng state.
+#ifdef MORE_HARDENED_PRNG
+    reset_sha256_state();
+#endif
+
     // for std::random_shuffle()
     srand(seed);
 }
@@ -87,11 +99,19 @@ unsigned long random_int( void )
 
 void push_rng_state()
 {
+#ifndef MORE_HARDENED_PRNG
     push_mt_state();
+#else
+    push_sha256_state();
+#endif
 }
 
 void pop_rng_state()
 {
+#ifndef MORE_HARDENED_PRNG
     pop_mt_state();
+#else
+    pop_sha256_state();
+#endif
 }
 
diff --git a/crawl-ref/source/sha256.cc b/crawl-ref/source/sha256.cc
index a36d316d92..96443587a0 100644
--- a/crawl-ref/source/sha256.cc
+++ b/crawl-ref/source/sha256.cc
@@ -11,12 +11,13 @@
 #include <stdint.h>
 
 typedef uint32_t u32;
-typedef uint64_t u64;
 
 #include "mt19937ar.h"
 
 #ifdef MORE_HARDENED_PRNG
 
+#include <stack>
+
 #include <cstring>
 #include <cstdio>
 #include <cstdlib>
@@ -137,12 +138,50 @@ void sha256chunk(const char* chunk, sha256state* ss)
     }
 }
 
-// 256 bits
-u32 mt_sha256_block[8], mt_block[8];
-u32 mt_block_index = 0;
+struct sha256mt_state
+{
+    // 256 bits
+    u32 mt_sha256_block[8], mt_block[8];
+    u32 mt_block_index;
+
+    sha256mt_state()
+    {
+        mt_block_index = 0;
+    }
+};
+
+sha256mt_state effective_state;
+
+std::stack<sha256mt_state> sha256mt_state_stack;
+
+void reset_sha256_state()
+{
+    effective_state.mt_block_index = 0;
+}
+
+void push_sha256_state()
+{
+    sha256mt_state_stack.push(effective_state);
+    push_mt_state();
+}
+
+void pop_sha256_state()
+{
+    if (sha256mt_state_stack.empty())
+        return;
+
+    effective_state = sha256mt_state_stack.top();
+
+    sha256mt_state_stack.pop();
+    pop_mt_state();
+}
 
 unsigned long sha256_genrand()
 {
+    u32 &mt_block_index = effective_state.mt_block_index;
+    u32 *mt_sha256_block = effective_state.mt_sha256_block;
+    u32 *mt_block = effective_state.mt_block;
+
     // Needs some hashing
     if (!(mt_block_index % 8))
     {
@@ -166,7 +205,21 @@ unsigned long sha256_genrand()
     return mt_sha256_block[mt_block_index++];
 }
 #else // MORE_HARDENED_PRNG
-// Stub this to MT function
+// Stub these to MT functions
+void push_sha256_state()
+{
+    push_mt_state();
+}
+
+void pop_sha256_state()
+{
+    pop_mt_state();
+}
+
+void reset_sha256_state()
+{
+}
+
 unsigned long sha256_genrand()
 {
     return genrand_int32();
diff --git a/crawl-ref/source/sha256.h b/crawl-ref/source/sha256.h
index 44986adc6b..6ddbb0a0c6 100644
--- a/crawl-ref/source/sha256.h
+++ b/crawl-ref/source/sha256.h
@@ -2,6 +2,10 @@
 #define sha256_h
 
 unsigned long sha256_genrand();
+void push_sha256_state();
+void pop_sha256_state();
+
+void reset_sha256_state();
 
 #endif