mirror of
https://github.com/pret/pokegold-spaceworld.git
synced 2026-08-09 11:47:38 -05:00
e1659ecd41
Addresses of sections will now be added to the linkerscript via `org`, and the section name will be the path/to/file. If there is more than one section in the file, then add a @SectionName after the path/to/file to describe the section.
69 lines
1.3 KiB
NASM
69 lines
1.3 KiB
NASM
include "constants.asm"
|
|
|
|
; if DEBUG
|
|
SECTION "home/random.asm", ROM0
|
|
; else
|
|
; SECTION "Random Number Generation", ROM0 [$3234]
|
|
; endc
|
|
|
|
Random::
|
|
; 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.
|
|
|
|
; This implementation also takes the current scanline as read from rLY
|
|
; and adds it nybble-swapped to the value of the divider. The unswapped
|
|
; value of rLY is also added to the value that's subtracted.
|
|
|
|
; Additionally, an equivalent function is executed in VBlank.
|
|
|
|
; This leaves a with the value in hRandomSub.
|
|
|
|
push bc
|
|
|
|
ldh a, [rLY]
|
|
ld c, a
|
|
swap a
|
|
ld b, a
|
|
ldh a, [rDIV]
|
|
adc b
|
|
ld b, a
|
|
ldh a, [hRandomAdd]
|
|
adc b
|
|
ldh [hRandomAdd], a
|
|
|
|
ldh a, [rLY]
|
|
swap a
|
|
ld b, a
|
|
ldh a, [rDIV]
|
|
adc b
|
|
adc c
|
|
ld b, a
|
|
ldh a, [hRandomSub]
|
|
sbc b
|
|
ldh [hRandomSub], a
|
|
|
|
pop bc
|
|
ret
|
|
|
|
BattleRandom::
|
|
; _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.
|
|
ldh a, [hROMBank]
|
|
push af
|
|
ld a, BANK(_BattleRandom)
|
|
call Bankswitch
|
|
|
|
call _BattleRandom
|
|
|
|
ld [wPredefHL + 1], a
|
|
pop af
|
|
call Bankswitch
|
|
ld a, [wPredefHL + 1]
|
|
ret |