source/libs/gmp/gmp-src/mpn/generic/toom2_sqr.c

   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 }