kc3-lang/libtommath/mp_invmod.c

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• Hash : ea654566
  Author :
  Date : 2020-02-23T09:46:12
  

  Give correct values for invmod with modulus of 1

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• mp_invmod.c

• #include "tommath_private.h"
  #ifdef MP_INVMOD_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* hac 14.61, pp608 */
  mp_err mp_invmod(const mp_int *a, const mp_int *b, mp_int *c)
  {
     /* for all n in N and n > 0, n = 0 mod 1 */
     if (!mp_isneg(a) && mp_cmp_d(b, 1uL) == MP_EQ) {
        mp_zero(c);
        return MP_OKAY;
     }
  
     /* b cannot be negative and has to be >1 */
     if (mp_isneg(b) || (mp_cmp_d(b, 1uL) != MP_GT)) {
        return MP_VAL;
     }
  
     /* if the modulus is odd we can use a faster routine instead */
     if (MP_HAS(S_MP_INVMOD_ODD) && mp_isodd(b)) {
        return s_mp_invmod_odd(a, b, c);
     }
  
     return MP_HAS(S_MP_INVMOD)
            ? s_mp_invmod(a, b, c)
            : MP_VAL;
  }
  #endif
  

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