/* 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, 2012,

2015 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 either:

  * 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.

or

  * the GNU General Public License as published by the Free Software

    Foundation; either version 2 of the License, or (at your option) any

    later version.

or both in parallel, as here.

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 General Public License

for more details.

You should have received copies of the GNU General Public License and the

GNU Lesser General Public License along with the GNU MP Library.  If not,

see https://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 (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) 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, mp_bitcnt_t 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 */

  wp = 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];

  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, mp_bitcnt_t cnt)

{

  cfdiv_q_2exp (w, u, cnt, 1);

}

void

mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)

{

  cfdiv_q_2exp (w, u, cnt, -1);

}