AMD 250 manual 191

25112 Rev. 3.06 September 2005 Software Optimization Guide for AMD64 Processors

"Division by Invariant Integers using Multiplication". SIGPLAN Notices, Vol. 29, June 1994, page 61.

*/

l = log2(d);

j = (((U64)(0x80000000)) % ((U64)(d)));

k = (((U64)(1)) << (32 + l)) / ((U64)(0x80000000 - j)); m_low = (((U64)(1)) << (32 + l)) / d;

m_high = ((((U64)(1)) << (32 + l)) + k) / d;

while (((m_low >> 1) < (m_high >> 1)) && (l > 0)) { m_low = m_low >> 1;

m_high = m_high >> 1; l = l - 1;

}

m= ((U32)(m_high)); s = l;

a = (m_high >> 31) ? 1 : 0;

if (a) {

printf("; dividend: memory location or register other than EAX or EDX\n");

printf("\n");
printf("MOV	EAX, 0%08LXh\n", m);
printf("IMUL	dividend\n");
printf("MOV	EAX, dividend\n");
printf("ADD	EDX, EAX\n");
if (s) printf("SAR		EDX, %d\n", s);
printf("SHR	EAX, 31\n");
printf("ADD	EDX, EAX\n");
if (e < 0) printf("NEG		EDX\n");
printf("\n");
printf("; quotient now in EDX\n");
}
else {
printf("; dividend: memory location of register other than EAX or EDX\n");
printf("\n");
printf("MOV	EAX, 0%08LXh\n", m);
printf("IMUL	dividend\n");
printf("MOV	EAX, dividend\n");
if (s) printf("SAR		EDX, %d\n", s);
printf("SHR	EAX, 31\n");
printf("ADD	EDX, EAX\n");
if (e < 0) printf("NEG		EDX\n");

printf("\n");

printf("; quotient now in EDX\n");

}

printed_code:

fprintf(stderr, "\n"); exit(0);

}

Chapter 8 Integer Optimizations 191