tdiv_q_2exp.c

来自「tpm-emulator 0.1版本tpm芯片的软件模拟版本」· C语言 代码 · 共 62 行

/* mpz_tdiv_q_2exp -- Divide an integer by 2**CNT.  Round the quotient
   towards -infinity.

Copyright 1991, 1993, 1994, 1996, 2001, 2002 Free Software Foundation, Inc.

This file is part of the GNU MP Library.

The GNU MP Library is free software; you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or (at your
option) any later version.

The GNU MP Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
License for more details.

You should have received a copy of the GNU Lesser General Public License
along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA. */

#include "gmp.h"
#include "gmp-impl.h"

void
mpz_tdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
{
  mp_size_t usize, wsize;
  mp_size_t limb_cnt;

  usize = u->_mp_size;
  limb_cnt = cnt / GMP_NUMB_BITS;
  wsize = ABS (usize) - limb_cnt;
  if (wsize <= 0)
    w->_mp_size = 0;
  else
    {
      mp_ptr wp;
      mp_srcptr up;

      if (w->_mp_alloc < wsize)
	_mpz_realloc (w, wsize);

      wp = w->_mp_d;
      up = u->_mp_d;

      cnt %= GMP_NUMB_BITS;
      if (cnt != 0)
	{
	  mpn_rshift (wp, up + limb_cnt, wsize, cnt);
	  wsize -= wp[wsize - 1] == 0;
	}
      else
	{
	  MPN_COPY_INCR (wp, up + limb_cnt, wsize);
	}

      w->_mp_size = usize >= 0 ? wsize : -wsize;
    }
}