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/*
Author: Pate Williams (c) 1997
14.54 Algorithm Binary gcd algorithm
See "Handbook of Applied Cryptography" by Alfred
J. Menezes et al page 606.
*/
#include
#include
#define DEBUG
long binary_gcd(long x, long y)
{
long g = 1, t;
#ifdef DEBUG
printf("-----------\n");
printf(" x y g\n");
printf("-----------\n");
#endif
while (!(x & 1) && !(y & 1))
x >>= 1, y >>= 1, g <<= 1;
while (x != 0) {
while (!(x & 1)) x >>= 1;
while (!(y & 1)) y >>= 1;
t = labs(x - y) >> 1;
if (x >= y) x = t; else y = t;
#ifdef DEBUG
printf("%3ld %3ld %3ld\n", x, y, g);
#endif
}
#ifdef DEBUG
printf("-----------\n");
#endif
return g * y;
}
int main(void)
{
long x = 1764, y = 868;
printf("x = %ld y = %ld\n", x, y);
printf("gcd(x, y) = %ld\n", binary_gcd(x, y));
return 0;
}