ref: b9684565fbfb51ba7d6da21446658ec56c498d50
dir: /engine/math/math.asm/
_Multiply:: ; hMultiplier is one byte. ld a, 8 ld b, a xor a ldh [hMultiplicand - 1], a ldh [hMathBuffer + 1], a ldh [hMathBuffer + 2], a ldh [hMathBuffer + 3], a ldh [hMathBuffer + 4], a .loop ldh a, [hMultiplier] srl a ldh [hMultiplier], a jr nc, .next ldh a, [hMathBuffer + 4] ld c, a ldh a, [hMultiplicand + 2] add c ldh [hMathBuffer + 4], a ldh a, [hMathBuffer + 3] ld c, a ldh a, [hMultiplicand + 1] adc c ldh [hMathBuffer + 3], a ldh a, [hMathBuffer + 2] ld c, a ldh a, [hMultiplicand + 0] adc c ldh [hMathBuffer + 2], a ldh a, [hMathBuffer + 1] ld c, a ldh a, [hMultiplicand - 1] adc c ldh [hMathBuffer + 1], a .next dec b jr z, .done ; hMultiplicand <<= 1 ldh a, [hMultiplicand + 2] add a ldh [hMultiplicand + 2], a ldh a, [hMultiplicand + 1] rla ldh [hMultiplicand + 1], a ldh a, [hMultiplicand + 0] rla ldh [hMultiplicand + 0], a ldh a, [hMultiplicand - 1] rla ldh [hMultiplicand - 1], a jr .loop .done ldh a, [hMathBuffer + 4] ldh [hProduct + 3], a ldh a, [hMathBuffer + 3] ldh [hProduct + 2], a ldh a, [hMathBuffer + 2] ldh [hProduct + 1], a ldh a, [hMathBuffer + 1] ldh [hProduct + 0], a ret _Divide:: xor a ldh [hMathBuffer + 0], a ldh [hMathBuffer + 1], a ldh [hMathBuffer + 2], a ldh [hMathBuffer + 3], a ldh [hMathBuffer + 4], a ld a, 9 ld e, a .loop ldh a, [hMathBuffer + 0] ld c, a ldh a, [hDividend + 1] sub c ld d, a ldh a, [hDivisor] ld c, a ldh a, [hDividend + 0] sbc c jr c, .next ldh [hDividend + 0], a ld a, d ldh [hDividend + 1], a ldh a, [hMathBuffer + 4] inc a ldh [hMathBuffer + 4], a jr .loop .next ld a, b cp 1 jr z, .done ldh a, [hMathBuffer + 4] add a ldh [hMathBuffer + 4], a ldh a, [hMathBuffer + 3] rla ldh [hMathBuffer + 3], a ldh a, [hMathBuffer + 2] rla ldh [hMathBuffer + 2], a ldh a, [hMathBuffer + 1] rla ldh [hMathBuffer + 1], a dec e jr nz, .next2 ld e, 8 ldh a, [hMathBuffer + 0] ldh [hDivisor], a xor a ldh [hMathBuffer + 0], a ldh a, [hDividend + 1] ldh [hDividend + 0], a ldh a, [hDividend + 2] ldh [hDividend + 1], a ldh a, [hDividend + 3] ldh [hDividend + 2], a .next2 ld a, e cp 1 jr nz, .okay dec b .okay ldh a, [hDivisor] srl a ldh [hDivisor], a ldh a, [hMathBuffer + 0] rr a ldh [hMathBuffer + 0], a jr .loop .done ldh a, [hDividend + 1] ldh [hRemainder], a ldh a, [hMathBuffer + 4] ldh [hQuotient + 3], a ldh a, [hMathBuffer + 3] ldh [hQuotient + 2], a ldh a, [hMathBuffer + 2] ldh [hQuotient + 1], a ldh a, [hMathBuffer + 1] ldh [hQuotient + 0], a ret