File: tsmemcmp.c

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#include "os.h"
#include <libsec.h>

/*
 * timing safe memcmp()
 */
int
tsmemcmp(void *a1, void *a2, ulong n)
{
	int lt, gt, c1, c2, r, m;
	uchar *s1, *s2;

	r = m = 0;
	s1 = a1;
	s2 = a2;
	while(n--){
		c1 = *s1++;
		c2 = *s2++;
		lt = (c1 - c2) >> 8;
		gt = (c2 - c1) >> 8;
		r |= (lt - gt) & ~m;
		m |= lt | gt;
	}
	return r;
}