source/libs/gmp/gmp-src/mpn/generic/add_err3_n.c

   1 /* mpn_add_err3_n -- add_n with three error terms
   2
   3    Contributed by David Harvey.
   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'LL CHANGE OR DISAPPEAR IN A FUTURE GNU MP RELEASE.
   8
   9 Copyright 2011 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 #include "gmp.h"
  38 #include "gmp-impl.h"
  39
  40 /*
  41   Computes:
  42
  43   (1) {rp,n} := {up,n} + {vp,n} (just like mpn_add_n) with incoming carry cy,
  44   return value is carry out.
  45
  46   (2) Let c[i+1] = carry from i-th limb addition (c[0] = cy).
  47   Computes c[1]*yp1[n-1] + ... + c[n]*yp1[0],
  48            c[1]*yp2[n-1] + ... + c[n]*yp2[0],
  49            c[1]*yp3[n-1] + ... + c[n]*yp3[0],
  50   stores two-limb results at {ep,2}, {ep+2,2} and {ep+4,2} respectively.
  51
  52   Requires n >= 1.
  53
  54   None of the outputs may overlap each other or any of the inputs, except
  55   that {rp,n} may be equal to {up,n} or {vp,n}.
  56 */
  57 mp_limb_t
  58 mpn_add_err3_n (mp_ptr rp, mp_srcptr up, mp_srcptr vp,
  59                 mp_ptr ep, mp_srcptr yp1, mp_srcptr yp2, mp_srcptr yp3,
  60                 mp_size_t n, mp_limb_t cy)
  61 {
  62   mp_limb_t el1, eh1, el2, eh2, el3, eh3, ul, vl, yl1, yl2, yl3, zl1, zl2, zl3, rl, sl, cy1, cy2;
  63
  64   ASSERT (n >= 1);
  65   ASSERT (MPN_SAME_OR_SEPARATE_P (rp, up, n));
  66   ASSERT (MPN_SAME_OR_SEPARATE_P (rp, vp, n));
  67   ASSERT (! MPN_OVERLAP_P (rp, n, yp1, n));
  68   ASSERT (! MPN_OVERLAP_P (rp, n, yp2, n));
  69   ASSERT (! MPN_OVERLAP_P (rp, n, yp3, n));
  70   ASSERT (! MPN_OVERLAP_P (ep, 6, up, n));
  71   ASSERT (! MPN_OVERLAP_P (ep, 6, vp, n));
  72   ASSERT (! MPN_OVERLAP_P (ep, 6, yp1, n));
  73   ASSERT (! MPN_OVERLAP_P (ep, 6, yp2, n));
  74   ASSERT (! MPN_OVERLAP_P (ep, 6, yp3, n));
  75   ASSERT (! MPN_OVERLAP_P (ep, 6, rp, n));
  76
  77   yp1 += n - 1;
  78   yp2 += n - 1;
  79   yp3 += n - 1;
  80   el1 = eh1 = 0;
  81   el2 = eh2 = 0;
  82   el3 = eh3 = 0;
  83
  84   do
  85     {
  86       yl1 = *yp1--;
  87       yl2 = *yp2--;
  88       yl3 = *yp3--;
  89       ul = *up++;
  90       vl = *vp++;
  91
  92       /* ordinary add_n */
  93       ADDC_LIMB (cy1, sl, ul, vl);
  94       ADDC_LIMB (cy2, rl, sl, cy);
  95       cy = cy1 | cy2;
  96       *rp++ = rl;
  97
  98       /* update (eh1:el1) */
  99       zl1 = (-cy) & yl1;
 100       el1 += zl1;
 101       eh1 += el1 < zl1;
 102
 103       /* update (eh2:el2) */
 104       zl2 = (-cy) & yl2;
 105       el2 += zl2;
 106       eh2 += el2 < zl2;
 107
 108       /* update (eh3:el3) */
 109       zl3 = (-cy) & yl3;
 110       el3 += zl3;
 111       eh3 += el3 < zl3;
 112     }
 113   while (--n);
 114
 115 #if GMP_NAIL_BITS != 0
 116   eh1 = (eh1 << GMP_NAIL_BITS) + (el1 >> GMP_NUMB_BITS);
 117   el1 &= GMP_NUMB_MASK;
 118   eh2 = (eh2 << GMP_NAIL_BITS) + (el2 >> GMP_NUMB_BITS);
 119   el2 &= GMP_NUMB_MASK;
 120   eh3 = (eh3 << GMP_NAIL_BITS) + (el3 >> GMP_NUMB_BITS);
 121   el3 &= GMP_NUMB_MASK;
 122 #endif
 123
 124   ep[0] = el1;
 125   ep[1] = eh1;
 126   ep[2] = el2;
 127   ep[3] = eh2;
 128   ep[4] = el3;
 129   ep[5] = eh3;
 130
 131   return cy;
 132 }