stdlib/mul_1.c

   1 /* mpn_mul_1 -- Multiply a limb vector with a single limb and
   2    store the product in a second limb vector.
   3
   4 Copyright (C) 1991-2020 Free Software Foundation, Inc.
   5
   6 This file is part of the GNU MP Library.
   7
   8 The GNU MP Library is free software; you can redistribute it and/or modify
   9 it under the terms of the GNU Lesser General Public License as published by
  10 the Free Software Foundation; either version 2.1 of the License, or (at your
  11 option) any later version.
  12
  13 The GNU MP Library is distributed in the hope that it will be useful, but
  14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MP Library; see the file COPYING.LIB.  If not, see
  20 <https://www.gnu.org/licenses/>.  */
  21
  22 #include <gmp.h>
  23 #include "gmp-impl.h"
  24 #include "longlong.h"
  25
  26 mp_limb_t
  27 mpn_mul_1 (register mp_ptr res_ptr, register mp_srcptr s1_ptr,
  28            mp_size_t s1_size, register mp_limb_t s2_limb)
  29 {
  30   register mp_limb_t cy_limb;
  31   register mp_size_t j;
  32   register mp_limb_t prod_high, prod_low;
  33
  34   /* The loop counter and index J goes from -S1_SIZE to -1.  This way
  35      the loop becomes faster.  */
  36   j = -s1_size;
  37
  38   /* Offset the base pointers to compensate for the negative indices.  */
  39   s1_ptr -= j;
  40   res_ptr -= j;
  41
  42   cy_limb = 0;
  43   do
  44     {
  45       umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb);
  46
  47       prod_low += cy_limb;
  48       cy_limb = (prod_low < cy_limb) + prod_high;
  49
  50       res_ptr[j] = prod_low;
  51     }
  52   while (++j != 0);
  53
  54   return cy_limb;
  55 }