mirror of
https://github.com/blondie7575/GSCats.git
synced 2024-11-21 15:33:11 +00:00
53 lines
1.1 KiB
ArmAsm
53 lines
1.1 KiB
ArmAsm
;
|
|
; random.s
|
|
; GSCats
|
|
;
|
|
; Created by Quinn Dunki on 12/29/19.
|
|
;
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
; random
|
|
; A => Random 8 bits
|
|
; Y => Less random 8 bits
|
|
;
|
|
; Taken from https://codebase64.org/doku.php?id=base:16bit_xorshift_random_generator
|
|
; This routine is not very fast, but it'll do for now. It's intended
|
|
; for 6502 so we're making due with it.
|
|
;
|
|
rng_zp_low = RANDOML
|
|
rng_zp_high = RANDOMH
|
|
|
|
random:
|
|
SAVE_AXY
|
|
EMULATION
|
|
LDA rng_zp_high
|
|
LSR
|
|
LDA rng_zp_low
|
|
ROR
|
|
EOR rng_zp_high
|
|
STA rng_zp_high ; high part of x ^= x << 7 done
|
|
ROR ; A has now x >> 9 and high bit comes from low byte
|
|
EOR rng_zp_low
|
|
STA rng_zp_low ; x ^= x >> 9 and the low part of x ^= x << 7 done
|
|
EOR rng_zp_high
|
|
STA rng_zp_high ; x ^= x << 8 done
|
|
NATIVE
|
|
RESTORE_AXY
|
|
RTS
|
|
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
; seedRandom
|
|
; A = Seed
|
|
;
|
|
; Taken from https://codebase64.org/doku.php?id=base:16bit_xorshift_random_generator
|
|
;
|
|
seedRandom:
|
|
SAVE_AXY
|
|
EMULATION
|
|
STA rng_zp_low
|
|
LDA #0
|
|
STA rng_zp_high
|
|
NATIVE
|
|
RESTORE_AXY
|
|
rts
|