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Annotation of OpenXM_contrib/gmp/mpz/fdiv_q_2exp.c, Revision 1.1

1.1     ! maekawa     1: /* mpz_fdiv_q_2exp -- Divide an integer by 2**CNT.  Round the quotient
        !             2:    towards -infinity.
        !             3:
        !             4: Copyright (C) 1991, 1993, 1994, 1996 Free Software Foundation, Inc.
        !             5:
        !             6: This file is part of the GNU MP Library.
        !             7:
        !             8: The GNU MP Library is free software; you can redistribute it and/or modify
        !             9: it under the terms of the GNU Library General Public License as published by
        !            10: the Free Software Foundation; either version 2 of the License, or (at your
        !            11: option) any later version.
        !            12:
        !            13: The GNU MP Library is distributed in the hope that it will be useful, but
        !            14: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
        !            15: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
        !            16: License for more details.
        !            17:
        !            18: You should have received a copy of the GNU Library General Public License
        !            19: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
        !            20: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
        !            21: MA 02111-1307, USA. */
        !            22:
        !            23: #include "gmp.h"
        !            24: #include "gmp-impl.h"
        !            25:
        !            26: void
        !            27: #if __STDC__
        !            28: mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
        !            29: #else
        !            30: mpz_fdiv_q_2exp (w, u, cnt)
        !            31:      mpz_ptr w;
        !            32:      mpz_srcptr u;
        !            33:      unsigned long int cnt;
        !            34: #endif
        !            35: {
        !            36:   mp_size_t usize = u->_mp_size;
        !            37:   mp_size_t wsize;
        !            38:   mp_size_t abs_usize = ABS (usize);
        !            39:   mp_size_t limb_cnt;
        !            40:   mp_ptr wp;
        !            41:   mp_limb_t round = 0;
        !            42:
        !            43:   limb_cnt = cnt / BITS_PER_MP_LIMB;
        !            44:   wsize = abs_usize - limb_cnt;
        !            45:   if (wsize <= 0)
        !            46:     {
        !            47:       wp = w->_mp_d;
        !            48:       wsize = 0;
        !            49:       /* Set ROUND since we know we skip some non-zero words in this case.
        !            50:         Well, if U is zero, we don't, but then this will be taken care of
        !            51:         below, since rounding only really takes place for negative U.  */
        !            52:       round = 1;
        !            53:       wp[0] = 1;
        !            54:       w->_mp_size = -(usize < 0);
        !            55:       return;
        !            56:     }
        !            57:   else
        !            58:     {
        !            59:       mp_size_t i;
        !            60:       mp_ptr up;
        !            61:
        !            62:       /* Make sure there is enough space.  We make an extra limb
        !            63:         here to account for possible rounding at the end.  */
        !            64:       if (w->_mp_alloc < wsize + 1)
        !            65:        _mpz_realloc (w, wsize + 1);
        !            66:
        !            67:       wp = w->_mp_d;
        !            68:       up = u->_mp_d;
        !            69:
        !            70:       /* Set ROUND if we are about skip some non-zero limbs.  */
        !            71:       for (i = 0; i < limb_cnt && round == 0; i++)
        !            72:        round = up[i];
        !            73:
        !            74:       cnt %= BITS_PER_MP_LIMB;
        !            75:       if (cnt != 0)
        !            76:        {
        !            77:          round |= mpn_rshift (wp, up + limb_cnt, wsize, cnt);
        !            78:          wsize -= wp[wsize - 1] == 0;
        !            79:        }
        !            80:       else
        !            81:        {
        !            82:          MPN_COPY_INCR (wp, up + limb_cnt, wsize);
        !            83:        }
        !            84:     }
        !            85:
        !            86:   if (usize < 0 && round != 0)
        !            87:     {
        !            88:       mp_limb_t cy;
        !            89:       cy = mpn_add_1 (wp, wp, wsize, 1);
        !            90:       wp[wsize] = cy;
        !            91:       wsize += cy;
        !            92:     }
        !            93:   w->_mp_size = usize >= 0 ? wsize : -wsize;
        !            94: }