Legacy Document

Inside Macintosh: QuickDraw GX Environment and Utilities /

Chapter 8 - QuickDraw GX Mathematics / QuickDraw GX Mathematics Reference

Mathematical Functions / Fixed-Point Operations

FixedMultiply

You can use the FixedMultiply function to return the product of two numbers.

Fixed FixedMultiply (Fixed multiplicand, Fixed multiplier);

multiplicand

The number to be multiplied by the multiplier.

multiplier

The number by which the multiplicand is to be multiplied.

function result

The product of two numbers.

DESCRIPTION

The FixedMultiply function multiplies two fixed numbers. The format of the Fixed number returned depends on the respective number formats of the multiplicand and multiplier. The operation has a bias of 16 bits; in general, the bias of the resulting number is the sum of the biases of the input numbers, shifted right by 16 bits. If either the multiplicand or the multiplier is Fixed, the result of the FixedMultiply function will be the same fixed-point format as the other parameter (long, Fixed, or fract).

Table 8-3 shows the bias of the product for different combinations of formats. The dashed line indicates that the resulting bias is not equivalent to long, fixed, or fract. Use the rules of the operation to determine it.

FixedMultiply product bias

	long	fixed	fract
long	---	long	---
fixed	long	fixed	fract
fract	---	fract	---

SPECIAL CONSIDERATIONS

The FixedMultiply function does not pin its result in the case of an overflow; the result returned is modulo 65,536.