Legacy Document

Inside Macintosh: QuickDraw GX Environment and Utilities /

Chapter 8 - QuickDraw GX Mathematics / Using QuickDraw GX Mathematics

Determining the Highest Order Bit of a wide Number

You can use the WideScale function to obtain the bit number of the highest order bit in the absolute value of a wide number. Listing 8-3 shows how to use the WideScale function in a function that multiplies two numbers in long format. If the product is too big to fit in a long, the function shifts the product so that it fits into a long and returns the bit shift. This operation can be termed pseudo-floating-point.

Listing 8-7 Using the WideScale function to create a pseudo-floating-point function

long FloatMul(long a, long b, long *product)
{
   wide temp;
   long shift = WideScale(WideMultiply(a, b, &temp)) - 30;
   if (shift > 0)
      WideShift(&temp, shift);
   else
      shift = 0;
   if (product) *product = temp.lo;
   return shift;
}

The WideScale function is described on page 8-53.