contrib/gmp/mpz/tdiv_r_2exp.c

   1 /* mpz_tdiv_r_2exp -- Divide a integer by 2**CNT and produce a remainder.
   2
   3 Copyright 1991, 1993, 1994, 1995, 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_tdiv_r_2exp (mpz_ptr res, mpz_srcptr in, unsigned long int cnt)
  25 {
  26   mp_size_t in_size = ABS (in->_mp_size);
  27   mp_size_t res_size;
  28   mp_size_t limb_cnt = cnt / GMP_NUMB_BITS;
  29   mp_srcptr in_ptr = in->_mp_d;
  30
  31   if (in_size > limb_cnt)
  32     {
  33       /* The input operand is (probably) greater than 2**CNT.  */
  34       mp_limb_t x;
  35
  36       x = in_ptr[limb_cnt] & (((mp_limb_t) 1 << cnt % GMP_NUMB_BITS) - 1);
  37       if (x != 0)
  38         {
  39           res_size = limb_cnt + 1;
  40           if (res->_mp_alloc < res_size)
  41             _mpz_realloc (res, res_size);
  42
  43           res->_mp_d[limb_cnt] = x;
  44         }
  45       else
  46         {
  47           res_size = limb_cnt;
  48           MPN_NORMALIZE (in_ptr, res_size);
  49
  50           if (res->_mp_alloc < res_size)
  51             _mpz_realloc (res, res_size);
  52
  53           limb_cnt = res_size;
  54         }
  55     }
  56   else
  57     {
  58       /* The input operand is smaller than 2**CNT.  We perform a no-op,
  59          apart from that we might need to copy IN to RES.  */
  60       res_size = in_size;
  61       if (res->_mp_alloc < res_size)
  62         _mpz_realloc (res, res_size);
  63
  64       limb_cnt = res_size;
  65     }
  66
  67   if (res != in)
  68     MPN_COPY (res->_mp_d, in->_mp_d, limb_cnt);
  69   res->_mp_size = in->_mp_size >= 0 ? res_size : -res_size;
  70 }