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| author | Jesse Luehrs <doy@tozt.net> | 2014-10-09 15:50:06 -0400 |
|---|---|---|
| committer | Jesse Luehrs <doy@tozt.net> | 2014-10-09 15:50:06 -0400 |
| commit | 74e56d8c86ab7e1e373dbc5d2ed684a7094e316e (patch) | |
| tree | f2be1eb171ecb336cd95a2ecc2e3f377c970116b | |
| parent | d18fef977d1d29460ec08fe2b8f5d5d485b89161 (diff) | |
| download | nes-snake-74e56d8c86ab7e1e373dbc5d2ed684a7094e316e.tar.gz nes-snake-74e56d8c86ab7e1e373dbc5d2ed684a7094e316e.zip | |
better random number generation
| -rw-r--r-- | main.s | 73 |
1 files changed, 38 insertions, 35 deletions
@@ -41,6 +41,7 @@ direction DB ; 0: up, 1: down, 2: left, 3: right frame_skip DB frame_count DB rand_state DB +rand_out DB apple INSTANCEOF point .ENDE ; }}} @@ -476,52 +477,54 @@ end_game: ; {{{ STA game_state RTS ; }}} new_apple: ; {{{ - JSR rand - LDA rand_state - AND #%01111000 + JSR rand4 + LDA rand_out + ASL + ASL + ASL CLC ADC #$40 STA apple.x - JSR rand - LDA rand_state - AND #%01111000 + JSR rand4 + LDA rand_out + ASL + ASL + ASL CLC ADC #$3D STA apple.y RTS ; }}} -rand: ; {{{ - ; linear feedback shift register with taps at 8, 6, 5, and 4 - LDY rand_state - TYA - AND #%10000000 - STA rand_state - TYA - AND #%00100000 - ASL - ASL - EOR rand_state - STA rand_state - TYA - AND #%00010000 - ASL - ASL - ASL - EOR rand_state - STA rand_state - TYA - AND #%00001000 - ASL - ASL +rand4: ; {{{ + JSR rand1 + LDX rand_out + JSR rand1 + TXA ASL + ORA rand_out + TAX + JSR rand1 + TXA ASL - EOR rand_state - ROL - STA rand_state - TYA + ORA rand_out + TAX + JSR rand1 + TXA ASL - ORA rand_state - STA rand_state + ORA rand_out + STA rand_out RTS ; }}} +rand1: ; {{{ + ; galois linear feedback shift register with taps at 8, 6, 5, and 4 + LDA rand_state + AND #$01 + STA rand_out + LSR rand_state + LDA rand_out + BEQ + + LDA rand_state + EOR #%10111000 + STA rand_state ++ RTS ; }}} ; }}} ; data {{{ palette: ; {{{ |