gcc/gmp/mpz/cfdiv_q_2exp.c

/* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n.

Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002, 2004 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 3 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.  If not, see http://www.gnu.org/licenses/.  */

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


/* dir==1 for ceil, dir==-1 for floor */

static void __gmpz_cfdiv_q_2exp __GMP_PROTO ((REGPARM_3_1 (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir))) REGPARM_ATTR (1);
#define cfdiv_q_2exp(w,u,cnt,dir)  __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir))

REGPARM_ATTR (1) static void
cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt, int dir)
{
  mp_size_t  wsize, usize, abs_usize, limb_cnt, i;
  mp_srcptr  up;
  mp_ptr     wp;
  mp_limb_t  round, rmask;

  usize = SIZ (u);
  abs_usize = ABS (usize);
  limb_cnt = cnt / GMP_NUMB_BITS;
  wsize = abs_usize - limb_cnt;
  if (wsize <= 0)
    {
      /* u < 2**cnt, so result 1, 0 or -1 according to rounding */
      PTR(w)[0] = 1;
      SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir);
      return;
    }

  /* +1 limb to allow for mpn_add_1 below */
  MPZ_REALLOC (w, wsize+1);

  /* Check for rounding if direction matches u sign.
     Set round if we're skipping non-zero limbs.  */
  up = PTR(u);
  round = 0;
  rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0);
  if (rmask != 0)
    for (i = 0; i < limb_cnt && round == 0; i++)
      round = up[i];

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

  if (round != 0)
    {
      if (wsize != 0)
	{
          mp_limb_t cy;
	  cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
	  wp[wsize] = cy;
	  wsize += cy;
	}
      else
	{
	  /* We shifted something to zero.  */
	  wp[0] = 1;
	  wsize = 1;
	}
    }
  SIZ(w) = (usize >= 0 ? wsize : -wsize);
}


void
mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt)
{
  cfdiv_q_2exp (w, u, cnt, 1);
}

void
mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long cnt)
{
  cfdiv_q_2exp (w, u, cnt, -1);
}