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Giac_maj/libtommath-0.39/bn_mp_mul_d.c 1.9 KB
6663b6c9   adorian   projet complet av...
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  #include <tommath.h>
  #ifdef BN_MP_MUL_D_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.
   *
   * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com
   */
  
  /* multiply by a digit */
  int
  mp_mul_d (mp_int * a, mp_digit b, mp_int * c)
  {
    mp_digit u, *tmpa, *tmpc;
    mp_word  r;
    int      ix, res, olduse;
  
    /* make sure c is big enough to hold a*b */
    if (c->alloc < a->used + 2) {
      if ((res = mp_grow (c, a->used + 2)) != MP_OKAY) {
        return res;
      }
    }
  
    /* get the original destinations used count */
    olduse = c->used;
  
    /* set the sign */
    c->sign = a->sign;
  
    /* alias for a->dp [source] */
    tmpa = a->dp;
  
    /* alias for c->dp [dest] */
    tmpc = c->dp;
  
    /* zero carry */
    u = 0;
  
    /* compute columns */
    for (ix = 0; ix < a->used; ix++) {
      /* compute product and carry sum for this term */
      r       = ((mp_word) u) + ((mp_word)*tmpa++) * ((mp_word)b);
  
      /* mask off higher bits to get a single digit */
      *tmpc++ = (mp_digit) (r & ((mp_word) MP_MASK));
  
      /* send carry into next iteration */
      u       = (mp_digit) (r >> ((mp_word) DIGIT_BIT));
    }
  
    /* store final carry [if any] and increment ix offset  */
    *tmpc++ = u & ((mp_word) MP_MASK);
    ++ix;
    *tmpc++ = u >> ((mp_word) DIGIT_BIT);
    ++ix;
  
    /* now zero digits above the top */
    while (ix++ < olduse) {
       *tmpc++ = 0;
    }
  
    /* set used count */
    c->used = a->used + 2;
    mp_clamp(c);
  
    return MP_OKAY;
  }
  #endif
  
  /* $Source: /cvs/libtom/libtommath/bn_mp_mul_d.c,v $ */
  /* $Revision: 1.3 $ */
  /* $Date: 2006/03/31 14:18:44 $ */