mpinvert.c (403B)
1 #include "os.h" 2 #include <mp.h> 3 4 #define iseven(a) (((a)->p[0] & 1) == 0) 5 6 /* use extended gcd to find the multiplicative inverse */ 7 /* res = b**-1 mod m */ 8 void 9 mpinvert(mpint *b, mpint *m, mpint *res) 10 { 11 mpint *dc1, *dc2; /* don't care */ 12 13 dc1 = mpnew(0); 14 dc2 = mpnew(0); 15 mpextendedgcd(b, m, dc1, res, dc2); 16 if(mpcmp(dc1, mpone) != 0) 17 abort(); 18 mpmod(res, m, res); 19 mpfree(dc1); 20 mpfree(dc2); 21 }