ref: e11ef2b8d5d73fd8c56ee015c78b086aaf3daf02
dir: /engine/math.asm/
_Multiply:: ; 66de ; hMultiplier is one byte. ld a, 8 ld b, a xor a ld [hProduct], a ld [hMathBuffer + 1], a ld [hMathBuffer + 2], a ld [hMathBuffer + 3], a ld [hMathBuffer + 4], a .loop ld a, [hMultiplier] srl a ld [hMultiplier], a jr nc, .next ld a, [hMathBuffer + 4] ld c, a ld a, [hMultiplicand + 2] add c ld [hMathBuffer + 4], a ld a, [hMathBuffer + 3] ld c, a ld a, [hMultiplicand + 1] adc c ld [hMathBuffer + 3], a ld a, [hMathBuffer + 2] ld c, a ld a, [hMultiplicand + 0] adc c ld [hMathBuffer + 2], a ld a, [hMathBuffer + 1] ld c, a ld a, [hProduct] adc c ld [hMathBuffer + 1], a .next dec b jr z, .done ; hMultiplicand <<= 1 ld a, [hMultiplicand + 2] add a ld [hMultiplicand + 2], a ld a, [hMultiplicand + 1] rla ld [hMultiplicand + 1], a ld a, [hMultiplicand + 0] rla ld [hMultiplicand + 0], a ld a, [hProduct] rla ld [hProduct], a jr .loop .done ld a, [hMathBuffer + 4] ld [hProduct + 3], a ld a, [hMathBuffer + 3] ld [hProduct + 2], a ld a, [hMathBuffer + 2] ld [hProduct + 1], a ld a, [hMathBuffer + 1] ld [hProduct + 0], a ret ; 673e _Divide:: ; 673e xor a ld [hMathBuffer + 0], a ld [hMathBuffer + 1], a ld [hMathBuffer + 2], a ld [hMathBuffer + 3], a ld [hMathBuffer + 4], a ld a, 9 ld e, a .loop ld a, [hMathBuffer + 0] ld c, a ld a, [hDividend + 1] sub c ld d, a ld a, [hDivisor] ld c, a ld a, [hDividend + 0] sbc c jr c, .next ld [hDividend + 0], a ld a, d ld [hDividend + 1], a ld a, [hMathBuffer + 4] inc a ld [hMathBuffer + 4], a jr .loop .next ld a, b cp 1 jr z, .done ld a, [hMathBuffer + 4] add a ld [hMathBuffer + 4], a ld a, [hMathBuffer + 3] rla ld [hMathBuffer + 3], a ld a, [hMathBuffer + 2] rla ld [hMathBuffer + 2], a ld a, [hMathBuffer + 1] rla ld [hMathBuffer + 1], a dec e jr nz, .next2 ld e, 8 ld a, [hMathBuffer + 0] ld [hDivisor], a xor a ld [hMathBuffer + 0], a ld a, [hDividend + 1] ld [hDividend + 0], a ld a, [hDividend + 2] ld [hDividend + 1], a ld a, [hDividend + 3] ld [hDividend + 2], a .next2 ld a, e cp 1 jr nz, .okay dec b .okay ld a, [hDivisor] srl a ld [hDivisor], a ld a, [hMathBuffer + 0] rr a ld [hMathBuffer + 0], a jr .loop .done ld a, [hDividend + 1] ld [hDivisor], a ld a, [hMathBuffer + 4] ld [hDividend + 3], a ld a, [hMathBuffer + 3] ld [hDividend + 2], a ld a, [hMathBuffer + 2] ld [hDividend + 1], a ld a, [hMathBuffer + 1] ld [hDividend + 0], a ret ; 67c1