kc3-lang/libtommath/s_mp_mul_high.c

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• Hash : 5c335f84
  Author :
  Date : 2019-10-30T17:26:27
  

  rename mul/sqr functions for consistency, comba instead of fast suffix

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• s_mp_mul_high.c

• #include "tommath_private.h"
  #ifdef S_MP_MUL_HIGH_C
  /* LibTomMath, multiple-precision integer library -- Tom St Denis */
  /* SPDX-License-Identifier: Unlicense */
  
  /* multiplies |a| * |b| and does not compute the lower digs digits
   * [meant to get the higher part of the product]
   */
  mp_err s_mp_mul_high(const mp_int *a, const mp_int *b, mp_int *c, int digs)
  {
     mp_int   t;
     int      pa, pb, ix;
     mp_err   err;
  
     /* can we use the fast multiplier? */
     if (MP_HAS(S_MP_MUL_HIGH_COMBA)
         && ((a->used + b->used + 1) < MP_WARRAY)
         && (MP_MIN(a->used, b->used) < MP_MAXFAST)) {
        return s_mp_mul_high_comba(a, b, c, digs);
     }
  
     if ((err = mp_init_size(&t, a->used + b->used + 1)) != MP_OKAY) {
        return err;
     }
     t.used = a->used + b->used + 1;
  
     pa = a->used;
     pb = b->used;
     for (ix = 0; ix < pa; ix++) {
        int iy;
        mp_digit u = 0;
  
        for (iy = digs - ix; iy < pb; iy++) {
           /* calculate the double precision result */
           mp_word r = (mp_word)t.dp[ix + iy] +
                       ((mp_word)a->dp[ix] * (mp_word)b->dp[iy]) +
                       (mp_word)u;
  
           /* get the lower part */
           t.dp[ix + iy] = (mp_digit)(r & (mp_word)MP_MASK);
  
           /* carry the carry */
           u       = (mp_digit)(r >> (mp_word)MP_DIGIT_BIT);
        }
        t.dp[ix + pb] = u;
     }
     mp_clamp(&t);
     mp_exch(&t, c);
     mp_clear(&t);
     return MP_OKAY;
  }
  #endif
  

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