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Giac_maj/libtommath-0.39/bn_mp_mul_2d.c 1.98 KB
6663b6c9   adorian   projet complet av...
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  #include <tommath.h>
  #ifdef BN_MP_MUL_2D_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
   */
  
  /* shift left by a certain bit count */
  int mp_mul_2d (mp_int * a, int b, mp_int * c)
  {
    mp_digit d;
    int      res;
  
    /* copy */
    if (a != c) {
       if ((res = mp_copy (a, c)) != MP_OKAY) {
         return res;
       }
    }
  
    if (c->alloc < (int)(c->used + b/DIGIT_BIT + 1)) {
       if ((res = mp_grow (c, c->used + b / DIGIT_BIT + 1)) != MP_OKAY) {
         return res;
       }
    }
  
    /* shift by as many digits in the bit count */
    if (b >= (int)DIGIT_BIT) {
      if ((res = mp_lshd (c, b / DIGIT_BIT)) != MP_OKAY) {
        return res;
      }
    }
  
    /* shift any bit count < DIGIT_BIT */
    d = (mp_digit) (b % DIGIT_BIT);
    if (d != 0) {
      register mp_digit *tmpc, shift, mask, r, rr;
      register int x;
  
      /* bitmask for carries */
      mask = (((mp_digit)1) << d) - 1;
  
      /* shift for msbs */
      shift = DIGIT_BIT - d;
  
      /* alias */
      tmpc = c->dp;
  
      /* carry */
      r    = 0;
      for (x = 0; x < c->used; x++) {
        /* get the higher bits of the current word */
        rr = (*tmpc >> shift) & mask;
  
        /* shift the current word and OR in the carry */
        *tmpc = ((*tmpc << d) | r) & MP_MASK;
        ++tmpc;
  
        /* set the carry to the carry bits of the current word */
        r = rr;
      }
      
      /* set final carry */
      if (r != 0) {
         c->dp[(c->used)++] = r;
      }
    }
    mp_clamp (c);
    return MP_OKAY;
  }
  #endif
  
  /* $Source: /cvs/libtom/libtommath/bn_mp_mul_2d.c,v $ */
  /* $Revision: 1.3 $ */
  /* $Date: 2006/03/31 14:18:44 $ */