139 lines
1.9 KiB
NASM
139 lines
1.9 KiB
NASM
IF !DEF(RNG_ASM)
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DEF RNG_ASM EQU 1
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INCLUDE "globals.asm"
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SECTION "RNG Variables", WRAM0
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wRNGSeed: ds 4
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wPieceHistory: ds 4
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wNextPiece:: ds 1
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section "RNG Functions", ROM0
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RNGInit::
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; Do some bit fuckery on the seed using the gameboy's free-running timers.
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ld hl, wRNGSeed
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ldh a, [rDIV]
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xor a, [hl]
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ld [hl+], a
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ldh a, [rTIMA]
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xor a, [hl]
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ld [hl+], a
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ldh a, [rDIV]
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xor a, [hl]
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ld [hl+], a
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ldh a, [rTIMA]
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xor a, [hl]
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ld [hl], a
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; Initialize the next history.
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ld hl, wPieceHistory
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ld a, PIECE_Z
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ld [hl+], a
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ld [hl+], a
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ld a, PIECE_S
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ld [hl+], a
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ld [hl], a
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; Get the first piece and make sure it's not Z, S or O.
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: call NextPiece
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cp a, PIECE_Z
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jr z, :-
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cp a, PIECE_S
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jr z, :-
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cp a, PIECE_O
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jr z, :-
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; Store it.
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ld hl, wPieceHistory
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ld [hl], a
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ld hl, wNextPiece
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ld [hl], a
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ret
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GetNextPiece::
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ld e, 7
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: dec e
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jr z, :+
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call NextPiece
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ld hl, wPieceHistory
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cp a, [hl]
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jr z, :-
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inc hl
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cp a, [hl]
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jr z, :-
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inc hl
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cp a, [hl]
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jr z, :-
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inc hl
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cp a, [hl]
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jr z, :-
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: ld hl, wNextPiece
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ld [hl], a
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ld b, a
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ld hl, wPieceHistory+2
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ld a, [hl+]
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ld [hl], a
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ld hl, wPieceHistory+1
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ld a, [hl+]
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ld [hl], a
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ld hl, wPieceHistory
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ld a, [hl+]
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ld [hl-], a
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ld a, b
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ld [hl], a
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ret
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NextPiece:
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call NextByte
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and a, $07
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cp a, 7
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ret nz
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dec a
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ret
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NextByte:
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; Load seed
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ld hl,wRNGSeed+3
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ld a, [hl-]
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ld b, a
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ld a, [hl-]
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ld c, a
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ld a, [hl-]
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; Multiply by 0x01010101
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add [hl]
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ld d, a
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adc c
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ld c, a
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adc b
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ld b, a
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; Add 0x31415927 and write back
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ld a, [hl]
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add $27
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ld [hl+], a
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ld a, d
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adc $59
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ld [hl+], a
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ld a, c
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adc $41
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ld [hl+], a
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ld c, a
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ld a, b
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adc $31
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ld [hl], a
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ret
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ENDC
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