github.com/aergoio/aergo@v1.3.1/libtool/src/gmp-6.1.2/mpn/generic/toom2_sqr.c (about)

     1  /* mpn_toom2_sqr -- Square {ap,an}.
     2  
     3     Contributed to the GNU project by Torbjorn Granlund.
     4  
     5     THE FUNCTION IN THIS FILE IS INTERNAL WITH A MUTABLE INTERFACE.  IT IS ONLY
     6     SAFE TO REACH IT THROUGH DOCUMENTED INTERFACES.  IN FACT, IT IS ALMOST
     7     GUARANTEED THAT IT WILL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
     8  
     9  Copyright 2006-2010, 2012, 2014 Free Software Foundation, Inc.
    10  
    11  This file is part of the GNU MP Library.
    12  
    13  The GNU MP Library is free software; you can redistribute it and/or modify
    14  it under the terms of either:
    15  
    16    * the GNU Lesser General Public License as published by the Free
    17      Software Foundation; either version 3 of the License, or (at your
    18      option) any later version.
    19  
    20  or
    21  
    22    * the GNU General Public License as published by the Free Software
    23      Foundation; either version 2 of the License, or (at your option) any
    24      later version.
    25  
    26  or both in parallel, as here.
    27  
    28  The GNU MP Library is distributed in the hope that it will be useful, but
    29  WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
    30  or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    31  for more details.
    32  
    33  You should have received copies of the GNU General Public License and the
    34  GNU Lesser General Public License along with the GNU MP Library.  If not,
    35  see https://www.gnu.org/licenses/.  */
    36  
    37  
    38  #include "gmp.h"
    39  #include "gmp-impl.h"
    40  
    41  /* Evaluate in: -1, 0, +inf
    42  
    43    <-s--><--n-->
    44     ____ ______
    45    |_a1_|___a0_|
    46  
    47    v0  =  a0     ^2  #   A(0)^2
    48    vm1 = (a0- a1)^2  #  A(-1)^2
    49    vinf=      a1 ^2  # A(inf)^2
    50  */
    51  
    52  #if TUNE_PROGRAM_BUILD || WANT_FAT_BINARY
    53  #define MAYBE_sqr_toom2   1
    54  #else
    55  #define MAYBE_sqr_toom2							\
    56    (SQR_TOOM3_THRESHOLD >= 2 * SQR_TOOM2_THRESHOLD)
    57  #endif
    58  
    59  #define TOOM2_SQR_REC(p, a, n, ws)					\
    60    do {									\
    61      if (! MAYBE_sqr_toom2						\
    62  	|| BELOW_THRESHOLD (n, SQR_TOOM2_THRESHOLD))			\
    63        mpn_sqr_basecase (p, a, n);					\
    64      else								\
    65        mpn_toom2_sqr (p, a, n, ws);					\
    66    } while (0)
    67  
    68  void
    69  mpn_toom2_sqr (mp_ptr pp,
    70  	       mp_srcptr ap, mp_size_t an,
    71  	       mp_ptr scratch)
    72  {
    73    const int __gmpn_cpuvec_initialized = 1;
    74    mp_size_t n, s;
    75    mp_limb_t cy, cy2;
    76    mp_ptr asm1;
    77  
    78  #define a0  ap
    79  #define a1  (ap + n)
    80  
    81    s = an >> 1;
    82    n = an - s;
    83  
    84    ASSERT (0 < s && s <= n && s >= n - 1);
    85  
    86    asm1 = pp;
    87  
    88    /* Compute asm1.  */
    89    if (s == n)
    90      {
    91        if (mpn_cmp (a0, a1, n) < 0)
    92  	{
    93  	  mpn_sub_n (asm1, a1, a0, n);
    94  	}
    95        else
    96  	{
    97  	  mpn_sub_n (asm1, a0, a1, n);
    98  	}
    99      }
   100    else /* n - s == 1 */
   101      {
   102        if (a0[s] == 0 && mpn_cmp (a0, a1, s) < 0)
   103  	{
   104  	  mpn_sub_n (asm1, a1, a0, s);
   105  	  asm1[s] = 0;
   106  	}
   107        else
   108  	{
   109  	  asm1[s] = a0[s] - mpn_sub_n (asm1, a0, a1, s);
   110  	}
   111      }
   112  
   113  #define v0	pp				/* 2n */
   114  #define vinf	(pp + 2 * n)			/* s+s */
   115  #define vm1	scratch				/* 2n */
   116  #define scratch_out	scratch + 2 * n
   117  
   118    /* vm1, 2n limbs */
   119    TOOM2_SQR_REC (vm1, asm1, n, scratch_out);
   120  
   121    /* vinf, s+s limbs */
   122    TOOM2_SQR_REC (vinf, a1, s, scratch_out);
   123  
   124    /* v0, 2n limbs */
   125    TOOM2_SQR_REC (v0, ap, n, scratch_out);
   126  
   127    /* H(v0) + L(vinf) */
   128    cy = mpn_add_n (pp + 2 * n, v0 + n, vinf, n);
   129  
   130    /* L(v0) + H(v0) */
   131    cy2 = cy + mpn_add_n (pp + n, pp + 2 * n, v0, n);
   132  
   133    /* L(vinf) + H(vinf) */
   134    cy += mpn_add (pp + 2 * n, pp + 2 * n, n, vinf + n, s + s - n);
   135  
   136    cy -= mpn_sub_n (pp + n, pp + n, vm1, 2 * n);
   137  
   138    ASSERT (cy + 1  <= 3);
   139    ASSERT (cy2 <= 2);
   140  
   141    MPN_INCR_U (pp + 2 * n, s + s, cy2);
   142    if (LIKELY (cy <= 2))
   143      MPN_INCR_U (pp + 3 * n, s + s - n, cy);
   144    else
   145      MPN_DECR_U (pp + 3 * n, s + s - n, 1);
   146  }