c3-lang/libtommath/bn_mp_karatsuba_sqr.c

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• Hash : 8714ee55
  Author :
  Date : 2015-11-25T21:59:46
  

  remove register let the compiler find the best register optimization

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• bn_mp_karatsuba_sqr.c

• #include <tommath_private.h>
  #ifdef BN_MP_KARATSUBA_SQR_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, tstdenis82@gmail.com, http://libtom.org
   */
  
  /* Karatsuba squaring, computes b = a*a using three 
   * half size squarings
   *
   * See comments of karatsuba_mul for details.  It 
   * is essentially the same algorithm but merely 
   * tuned to perform recursive squarings.
   */
  int mp_karatsuba_sqr (mp_int * a, mp_int * b)
  {
    mp_int  x0, x1, t1, t2, x0x0, x1x1;
    int     B, err;
  
    err = MP_MEM;
  
    /* min # of digits */
    B = a->used;
  
    /* now divide in two */
    B = B >> 1;
  
    /* init copy all the temps */
    if (mp_init_size (&x0, B) != MP_OKAY)
      goto ERR;
    if (mp_init_size (&x1, a->used - B) != MP_OKAY)
      goto X0;
  
    /* init temps */
    if (mp_init_size (&t1, a->used * 2) != MP_OKAY)
      goto X1;
    if (mp_init_size (&t2, a->used * 2) != MP_OKAY)
      goto T1;
    if (mp_init_size (&x0x0, B * 2) != MP_OKAY)
      goto T2;
    if (mp_init_size (&x1x1, (a->used - B) * 2) != MP_OKAY)
      goto X0X0;
  
    {
      int x;
      mp_digit *dst, *src;
  
      src = a->dp;
  
      /* now shift the digits */
      dst = x0.dp;
      for (x = 0; x < B; x++) {
        *dst++ = *src++;
      }
  
      dst = x1.dp;
      for (x = B; x < a->used; x++) {
        *dst++ = *src++;
      }
    }
  
    x0.used = B;
    x1.used = a->used - B;
  
    mp_clamp (&x0);
  
    /* now calc the products x0*x0 and x1*x1 */
    if (mp_sqr (&x0, &x0x0) != MP_OKAY)
      goto X1X1;           /* x0x0 = x0*x0 */
    if (mp_sqr (&x1, &x1x1) != MP_OKAY)
      goto X1X1;           /* x1x1 = x1*x1 */
  
    /* now calc (x1+x0)**2 */
    if (s_mp_add (&x1, &x0, &t1) != MP_OKAY)
      goto X1X1;           /* t1 = x1 - x0 */
    if (mp_sqr (&t1, &t1) != MP_OKAY)
      goto X1X1;           /* t1 = (x1 - x0) * (x1 - x0) */
  
    /* add x0y0 */
    if (s_mp_add (&x0x0, &x1x1, &t2) != MP_OKAY)
      goto X1X1;           /* t2 = x0x0 + x1x1 */
    if (s_mp_sub (&t1, &t2, &t1) != MP_OKAY)
      goto X1X1;           /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
  
    /* shift by B */
    if (mp_lshd (&t1, B) != MP_OKAY)
      goto X1X1;           /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
    if (mp_lshd (&x1x1, B * 2) != MP_OKAY)
      goto X1X1;           /* x1x1 = x1x1 << 2*B */
  
    if (mp_add (&x0x0, &t1, &t1) != MP_OKAY)
      goto X1X1;           /* t1 = x0x0 + t1 */
    if (mp_add (&t1, &x1x1, b) != MP_OKAY)
      goto X1X1;           /* t1 = x0x0 + t1 + x1x1 */
  
    err = MP_OKAY;
  
  X1X1:mp_clear (&x1x1);
  X0X0:mp_clear (&x0x0);
  T2:mp_clear (&t2);
  T1:mp_clear (&t1);
  X1:mp_clear (&x1);
  X0:mp_clear (&x0);
  ERR:
    return err;
  }
  #endif
  
  /* $Source$ */
  /* $Revision$ */
  /* $Date$ */
  

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