diff options
| -rw-r--r-- | rand.s | 105 | ||||
| -rw-r--r-- | taipan.c | 6 |
2 files changed, 66 insertions, 45 deletions
@@ -1,17 +1,38 @@ - .export _randb, _randi, _randl + .export _randl + .import _rand +; .export _randb, _randi, _randl ; .export _rand1in5 ; .export _randbit .importzp sreg, tmp3 .include "atari.inc" -; RANDOM is the POKEY LFSR read address. This appears to be the low 8 -; bits of a 17-bit LFSR (Atari calls it a poly counter). Unfortunately, -; a read from this address will never return 0, since LFSR's can't do -; that. If Atari had made the RANDOM register read the higher order bits -; of the LFSR, rather than the bottom 8, this wouldn't be a problem... but -; they didn't, so there's extra code in here to (try to) compensate. +; unsigned long __fastcall__ randl(void); +; this returns the full range of an unsigned long, 0 to 2**32-1 +_randl: + jsr _rand + sta sreg + jsr _rand + sta sreg+1 + jsr _rand + sta tmp3 + jsr _rand + ldx tmp3 + rts + + ;;; rest of file is commented out + +; RANDOM is the POKEY LFSR read address. According to the POKEY data +; sheet, this is the high 8 bits bits of a 17-bit LFSR (Atari calls it +; a poly counter). Unfortunately, a read from this address never seems +; to return 0, which confuses me: an LFSR can never return 0, but since +; we're only reading 8 bits of it, we should be able to get a 0 (some +; of the other 9 bits would still be 1). + +; After some crude statistical analysis, I've decided to go with cc65's +; rand() implementation. It seems to return more evenly distributed +; results. ; Might use this at some point: ;_randbit: @@ -45,46 +66,46 @@ ; unsigned char __fastcall__ randb(void); -_randb: ; C-callable entry point - ldx #0 -randb: ; asm-callable (doesn't trash X reg) - lda RANDOM ; bit 7 of this read ends up as bit 0 of result - sta tmp3 - nop ; let the LFSR cook for a bit... - nop - lda RTCLOK+2 ; different amount of cooking depending on whether - and #$01 ; we're on an even or odd numbered TV frame - bne @1 - nop - nop - nop -@1: - rol tmp3 ; tmp3 bit 7 now in carry - lda RANDOM - rol ; carry now in bit 0 of A - nop - nop - rts +;;_randb: ; C-callable entry point +;; ldx #0 +;;randb: ; asm-callable (doesn't trash X reg) +;; lda RANDOM ; bit 7 of this read ends up as bit 0 of result +;; sta tmp3 +;; nop ; let the LFSR cook for a bit... +;; nop +;; lda RTCLOK+2 ; different amount of cooking depending on whether +;; and #$01 ; we're on an even or odd numbered TV frame +;; bne @1 +;; nop +;; nop +;; nop +;;@1: +;; rol tmp3 ; tmp3 bit 7 now in carry +;; lda RANDOM +;; rol ; carry now in bit 0 of A +;; nop +;; nop +;; rts ; unsigned int __fastcall__ randi(void); ; NB cc65's rand() returns a positive signed int, meaning ; 0 to 0x7fff. -_randi: - jsr randb - and #$7f - tax - jsr randb - rts +;;_randi: +;; jsr randb +;; and #$7f +;; tax +;; jsr randb +;; rts ; unsigned long __fastcall__ randl(void); ; this returns the full range of an unsigned long, 0 to 2**32-1 -_randl: - jsr randb - sta sreg - jsr randb - sta sreg+1 - jsr randb - tax - jsr randb - rts +;;_randl: +;; jsr randb +;; sta sreg +;; jsr randb +;; sta sreg+1 +;; jsr randb +;; tax +;; jsr randb +;; rts @@ -14,8 +14,8 @@ #endif /* define this to use cc65's rand() instead of POKEY's RANDOM - register. No need to disable this now */ -#define POKEY_RANDOM + register. Disabled for now, maybe forever (pending testing) */ +// #define POKEY_RANDOM /**** These defines should be disabled for normal gameplay. Don't leave any of them enabled for a release or a @@ -3003,8 +3003,8 @@ int main(void) { bignum_test(); #endif - initrand(); name_firm(); + initrand(); cash_or_guns(); set_prices(); |