text: #include "tommath_private.h"
  #ifdef BN_MP_MUL_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis
   *
   * LibTomMath is a library that provides multiple-precision
   * integer arithmetic as well as number theoretic functionality.
   *
   * The library was designed directly after the MPI library by
   * Michael Fromberger but has been written from scratch with
   * additional optimizations in place.
   *
   * The library is free for all purposes without any express
   * guarantee it works.
   */
  
  /* high level multiplication (handles sign) */
  int mp_mul(const mp_int *a, const mp_int *b, mp_int *c)
  {
     int     res, neg;
     neg = (a->sign == b->sign) ? MP_ZPOS : MP_NEG;
  
     /* use Toom-Cook? */
  #ifdef BN_MP_TOOM_MUL_C
     if (MIN(a->used, b->used) >= TOOM_MUL_CUTOFF) {
        res = mp_toom_mul(a, b, c);
     } else
  #endif
  #ifdef BN_MP_KARATSUBA_MUL_C
        /* use Karatsuba? */
        if (MIN(a->used, b->used) >= KARATSUBA_MUL_CUTOFF) {
           res = mp_karatsuba_mul(a, b, c);
        } else
  #endif
        {
           /* can we use the fast multiplier?
            *
            * The fast multiplier can be used if the output will
            * have less than MP_WARRAY digits and the number of
            * digits won't affect carry propagation
            */
           int     digs = a->used + b->used + 1;
  
  #ifdef BN_FAST_S_MP_MUL_DIGS_C
           if ((digs < (int)MP_WARRAY) &&
               (MIN(a->used, b->used) <=
                (int)(1u << (((size_t)CHAR_BIT * sizeof(mp_word)) - (2u * (size_t)DIGIT_BIT))))) {
              res = fast_s_mp_mul_digs(a, b, c, digs);
           } else
  #endif
           {
  #ifdef BN_S_MP_MUL_DIGS_C
              res = s_mp_mul(a, b, c); /* uses s_mp_mul_digs */
  #else
              res = MP_VAL;
  #endif
           }
        }
     c->sign = (c->used > 0) ? neg : MP_ZPOS;
     return res;
  }
  #endif
  
  /* ref:         HEAD -> develop */
  /* git commit:  8b9f98baa16b21e1612ac6746273febb74150a6f */
  /* commit time: 2018-09-23 21:37:58 +0200 */
  