mirror of
https://gitlab.com/xCrystal/pokecrystal-board.git
synced 2024-09-09 09:51:34 -07:00
77 lines
1.2 KiB
NASM
77 lines
1.2 KiB
NASM
Random: ; 2f8c
|
|
; A simple hardware-based random number generator (RNG).
|
|
|
|
; Two random numbers are generated by adding and subtracting
|
|
; the divider to the respective values every time it's called.
|
|
|
|
; The divider is a register that increments at a rate of 16384Hz.
|
|
; For comparison, the Game Boy operates at a clock speed of 4.2MHz.
|
|
|
|
; Additionally, an equivalent function is executed in VBlank.
|
|
|
|
; This leaves a with the value in hRandomSub.
|
|
|
|
push bc
|
|
|
|
ld a, [rDIV]
|
|
ld b, a
|
|
ld a, [hRandomAdd]
|
|
adc b
|
|
ld [hRandomAdd], a
|
|
|
|
ld a, [rDIV]
|
|
ld b, a
|
|
ld a, [hRandomSub]
|
|
sbc b
|
|
ld [hRandomSub], a
|
|
|
|
pop bc
|
|
ret
|
|
; 2f9f
|
|
|
|
BattleRandom: ; 2f9f
|
|
; _BattleRandom lives in another bank.
|
|
|
|
; It handles all RNG calls in the battle engine, allowing
|
|
; link battles to remain in sync using a shared PRNG.
|
|
|
|
ld a, [hROMBank]
|
|
push af
|
|
ld a, BANK(_BattleRandom)
|
|
rst Bankswitch
|
|
|
|
call _BattleRandom
|
|
|
|
ld [$cfb6], a
|
|
pop af
|
|
rst Bankswitch
|
|
ld a, [$cfb6]
|
|
ret
|
|
; 2fb1
|
|
|
|
|
|
Function2fb1: ; 2fb1
|
|
push bc
|
|
ld c, a
|
|
xor a
|
|
sub c
|
|
.asm_2fb5
|
|
sub c
|
|
jr nc, .asm_2fb5
|
|
add c
|
|
ld b, a
|
|
push bc
|
|
.asm_2fbb
|
|
call Random
|
|
ld a, [hRandomAdd]
|
|
ld c, a
|
|
add b
|
|
jr c, .asm_2fbb
|
|
ld a, c
|
|
pop bc
|
|
call SimpleDivide
|
|
pop bc
|
|
ret
|
|
; 2fcb
|
|
|