ref: caef73363f896a1405ce6b9b6435f91e47a9b188
dir: /libmp/port/mpinvert.c/
#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 int r; dc1 = mpnew(0); dc2 = mpnew(0); mpextendedgcd(b, m, dc1, res, dc2); r = mpcmp(dc1, mpone); mpfree(dc1); mpfree(dc2); if(r != 0) sysfatal("mpinvert: no inverse"); mpmod(res, m, res); }