AMD 250 manual 187

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

fprintf(stderr, "enter divisor: "); scanf("%lu", &d);

printf("\n");

if (d == 0) goto printed_code;

if (d >= 0x80000000UL)		{
printf("; dividend: register or memory location\n");
printf("\n");
printf("CMP	dividend, 0%08lXh\n", d);
printf("MOV	EDX, 0\n");
printf("SBB	EDX, -1\n");
printf("\n");

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

}

/* Reduce divisor until it becomes odd. */

n = 0;
t = d;
while	(!(t & 1)) {
t >>= 1;
n++;
}
if (t	== 1) {
if	(n == 0) {
	printf("; dividend: register or memory location\n");
	printf("\n");
	printf("MOV	EDX, dividend\n", n);
	printf("\n");
	printf("; quotient now in EDX\n");
}
else {
	printf("; dividend: register or memory location\n");
	printf("\n");
	printf("SHR	dividend, %d\n", n);
	printf("\n");

printf("; quotient replaced dividend\n");

}

goto printed_code;

}

/* Generate m, s for algorithm 0. Based on: Granlund, T.; Montgomery, P.L.: "Division by Invariant Integers using Multiplication." SIGPLAN Notices, Vol. 29, June 1994, page 61.

*/

l = log2(t) + 1;

Chapter 8 Integer Optimizations 187