contrib/gmp/mpz/mul_2exp.c

   1 /* mpz_mul_2exp -- Multiply a bignum by 2**CNT
   2
   3 Copyright 1991, 1993, 1994, 1996, 2001, 2002 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 3 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22
  23 void
  24 mpz_mul_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
  25 {
  26   mp_size_t usize = u->_mp_size;
  27   mp_size_t abs_usize = ABS (usize);
  28   mp_size_t wsize;
  29   mp_size_t limb_cnt;
  30   mp_ptr wp;
  31   mp_limb_t wlimb;
  32
  33   if (usize == 0)
  34     {
  35       w->_mp_size = 0;
  36       return;
  37     }
  38
  39   limb_cnt = cnt / GMP_NUMB_BITS;
  40   wsize = abs_usize + limb_cnt + 1;
  41   if (w->_mp_alloc < wsize)
  42     _mpz_realloc (w, wsize);
  43
  44   wp = w->_mp_d;
  45   wsize = abs_usize + limb_cnt;
  46
  47   cnt %= GMP_NUMB_BITS;
  48   if (cnt != 0)
  49     {
  50       wlimb = mpn_lshift (wp + limb_cnt, u->_mp_d, abs_usize, cnt);
  51       if (wlimb != 0)
  52         {
  53           wp[wsize] = wlimb;
  54           wsize++;
  55         }
  56     }
  57   else
  58     {
  59       MPN_COPY_DECR (wp + limb_cnt, u->_mp_d, abs_usize);
  60     }
  61
  62   /* Zero all whole limbs at low end.  Do it here and not before calling
  63      mpn_lshift, not to lose for U == W.  */
  64   MPN_ZERO (wp, limb_cnt);
  65
  66   w->_mp_size = usize >= 0 ? wsize : -wsize;
  67 }