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#include "os.h"
#include <mp.h>
#define iseven(a) (((a)->p[0] & 1) == 0)
// use extended gcd to find the multiplicative inverse
// res = b**-1 mod m
void
mpinvert(mpint *b, mpint *m, mpint *res)
{
mpint *dc1, *dc2; // don't care
dc1 = mpnew(0);
dc2 = mpnew(0);
mpextendedgcd(b, m, dc1, res, dc2);
if(mpcmp(dc1, mpone) != 0)
abort();
mpmod(res, m, res);
mpfree(dc1);
mpfree(dc2);
}
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