EarthBound/ASM/Math Routines

This is a sub-page of EarthBound/ASM.

$C08FE8-$C08FF6: Unsigned 8-bit multiplication

accumulator[0] = accumulator[0] * accumulator[1]

Multiplies two 8-bit multiplicands and truncates the product into an 8-bit result. Implemented using a simple application of the SNES's hardware support for unsigned multiplication.

Note: This routine does not appear to be used anywhere in an unmodified EarthBound ROM.

Inputs

• accumulator[0]: 8-bit multiplicand1
• accumulator[1]: 8-bit multiplicand2

Outputs

• accumulator: 8-bit product

Note: The accumulator is set to 8-bit mode before returning because somebody was trying way too hard to stick to the principle that an 8-bit math operation should always return an 8-bit result. But if you clear flag #$20 after the routine returns, the upper byte of the accumulator should contain the upper byte of the product for a full 16-bit result.

$C08FF7-$C09031: Unsigned 16-bit * 8-bit multiplication

accumulator = accumulator * y[0]

Multiplies a 16-bit multiplicand by an 8-bit multiplicand and truncates the product into a 16-bit result. Implemented by combining together the results of up to two applications of the SNES hardware multiplier.

Inputs

• accumulator: 16-bit multiplicand1
• y[0]: 8-bit multiplicand2

Outputs

• accumulator: 16-bit product

Note: Due to how the result is processed, if the input accumulator[1] is not zero, on output, y[1] will contain the upper third byte of the product, making it possible to use this routine to calculate a 24-bit product. But if the input accumulator[1] is zero, y[1] will not be modified, and will contain whatever it contained before calling the routine.

$C091A6-$C091E2: Unsigned 32-bit division

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