95 lines
2.5 KiB
C
95 lines
2.5 KiB
C
/* mpz_fdiv_q_2exp -- Divide an integer by 2**CNT. Round the quotient
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towards -infinity.
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Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
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This file is part of the GNU MP Library.
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The GNU MP Library is free software; you can redistribute it and/or modify
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it under the terms of the GNU Library General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at your
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option) any later version.
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The GNU MP Library is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Library General Public
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License for more details.
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You should have received a copy of the GNU Library General Public License
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along with the GNU MP Library; see the file COPYING.LIB. If not, write to
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the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
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MA 02111-1307, USA. */
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#include "gmp.h"
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#include "gmp-impl.h"
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void
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#if __STDC__
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mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
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#else
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mpz_fdiv_q_2exp (w, u, cnt)
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mpz_ptr w;
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mpz_srcptr u;
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unsigned long int cnt;
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#endif
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{
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mp_size_t usize = u->_mp_size;
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mp_size_t wsize;
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mp_size_t abs_usize = ABS (usize);
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mp_size_t limb_cnt;
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mp_ptr wp;
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mp_limb_t round = 0;
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limb_cnt = cnt / BITS_PER_MP_LIMB;
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wsize = abs_usize - limb_cnt;
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if (wsize <= 0)
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{
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wp = w->_mp_d;
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wsize = 0;
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/* Set ROUND since we know we skip some non-zero words in this case.
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Well, if U is zero, we don't, but then this will be taken care of
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below, since rounding only really takes place for negative U. */
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round = 1;
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wp[0] = 1;
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w->_mp_size = -(usize < 0);
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return;
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}
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else
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{
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mp_size_t i;
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mp_ptr up;
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/* Make sure there is enough space. We make an extra limb
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here to account for possible rounding at the end. */
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if (w->_mp_alloc < wsize + 1)
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_mpz_realloc (w, wsize + 1);
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wp = w->_mp_d;
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up = u->_mp_d;
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/* Set ROUND if we are about skip some non-zero limbs. */
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for (i = 0; i < limb_cnt && round == 0; i++)
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round = up[i];
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cnt %= BITS_PER_MP_LIMB;
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if (cnt != 0)
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{
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round |= mpn_rshift (wp, up + limb_cnt, wsize, cnt);
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wsize -= wp[wsize - 1] == 0;
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}
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else
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{
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MPN_COPY_INCR (wp, up + limb_cnt, wsize);
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}
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}
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if (usize < 0 && round != 0)
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{
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mp_limb_t cy;
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cy = mpn_add_1 (wp, wp, wsize, 1);
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wp[wsize] = cy;
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wsize += cy;
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}
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w->_mp_size = usize >= 0 ? wsize : -wsize;
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}
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