Legacy Document

Inside Macintosh: QuickDraw GX Environment and Utilities /

Chapter 8 - QuickDraw GX Mathematics / QuickDraw GX Mathematics Reference

Mathematical Functions / Fixed-Point Operations

FractMultiply

You can use the FractMultiply function to calculate the product of two numbers.

fract FractMultiply (fract multiplicand, fract multiplier);

multiplicand

The number to be multiplied by the multiplier.

multiplier

The number by which the multiplicand is to multiplied.

function result

The product of two numbers.

DESCRIPTION

The FractMultiply function calculates the product of two numbers, specified in the multiplicand and multiplier parameters. If the parameters are a and b, the product a b is returned.

The format of the number returned depends on the respective number formats of the multiplicand and multiplier parameters. The operation has a bias of 30 bits; in general, the bias of the resulting number is the sum of the biases of the input numbers, shifted right by 30 bits. Thus if either the multiplicand or multiplier parameter is fract, then the result is the same fixed-point format as the other argument.

Table 8-5 shows the bias of the FractMultiply result. 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

FractMultiply result bias

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

SPECIAL CONSIDERATIONS

FractMultiply does not pin its result in the case of an overflow; the result returned is modulo 4.