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Annotation of OpenXM_contrib/gmp/mpz/fdiv_q_2exp.c, Revision 1.1.1.2

1.1       maekawa     1: /* mpz_fdiv_q_2exp -- Divide an integer by 2**CNT.  Round the quotient
                      2:    towards -infinity.
                      3:
1.1.1.2 ! maekawa     4: Copyright (C) 1991, 1993, 1994, 1996, 1998, 1999 Free Software Foundation,
        !             5: Inc.
1.1       maekawa     6:
                      7: This file is part of the GNU MP Library.
                      8:
                      9: The GNU MP Library is free software; you can redistribute it and/or modify
1.1.1.2 ! maekawa    10: it under the terms of the GNU Lesser General Public License as published by
        !            11: the Free Software Foundation; either version 2.1 of the License, or (at your
1.1       maekawa    12: option) any later version.
                     13:
                     14: The GNU MP Library is distributed in the hope that it will be useful, but
                     15: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
1.1.1.2 ! maekawa    16: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
1.1       maekawa    17: License for more details.
                     18:
1.1.1.2 ! maekawa    19: You should have received a copy of the GNU Lesser General Public License
1.1       maekawa    20: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     21: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     22: MA 02111-1307, USA. */
                     23:
                     24: #include "gmp.h"
                     25: #include "gmp-impl.h"
                     26:
                     27: void
                     28: #if __STDC__
                     29: mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, unsigned long int cnt)
                     30: #else
                     31: mpz_fdiv_q_2exp (w, u, cnt)
                     32:      mpz_ptr w;
                     33:      mpz_srcptr u;
                     34:      unsigned long int cnt;
                     35: #endif
                     36: {
                     37:   mp_size_t usize = u->_mp_size;
                     38:   mp_size_t wsize;
                     39:   mp_size_t abs_usize = ABS (usize);
                     40:   mp_size_t limb_cnt;
                     41:   mp_ptr wp;
                     42:   mp_limb_t round = 0;
                     43:
                     44:   limb_cnt = cnt / BITS_PER_MP_LIMB;
                     45:   wsize = abs_usize - limb_cnt;
                     46:   if (wsize <= 0)
                     47:     {
                     48:       wp = w->_mp_d;
                     49:       wsize = 0;
                     50:       /* Set ROUND since we know we skip some non-zero words in this case.
                     51:         Well, if U is zero, we don't, but then this will be taken care of
                     52:         below, since rounding only really takes place for negative U.  */
                     53:       round = 1;
                     54:       wp[0] = 1;
                     55:       w->_mp_size = -(usize < 0);
                     56:       return;
                     57:     }
                     58:   else
                     59:     {
                     60:       mp_size_t i;
                     61:       mp_ptr up;
                     62:
                     63:       /* Make sure there is enough space.  We make an extra limb
                     64:         here to account for possible rounding at the end.  */
                     65:       if (w->_mp_alloc < wsize + 1)
                     66:        _mpz_realloc (w, wsize + 1);
                     67:
                     68:       wp = w->_mp_d;
                     69:       up = u->_mp_d;
                     70:
                     71:       /* Set ROUND if we are about skip some non-zero limbs.  */
                     72:       for (i = 0; i < limb_cnt && round == 0; i++)
                     73:        round = up[i];
                     74:
                     75:       cnt %= BITS_PER_MP_LIMB;
                     76:       if (cnt != 0)
                     77:        {
                     78:          round |= mpn_rshift (wp, up + limb_cnt, wsize, cnt);
                     79:          wsize -= wp[wsize - 1] == 0;
                     80:        }
                     81:       else
                     82:        {
                     83:          MPN_COPY_INCR (wp, up + limb_cnt, wsize);
                     84:        }
                     85:     }
                     86:
                     87:   if (usize < 0 && round != 0)
                     88:     {
                     89:       mp_limb_t cy;
1.1.1.2 ! maekawa    90:       if (wsize != 0)
        !            91:        {
        !            92:          cy = mpn_add_1 (wp, wp, wsize, (mp_limb_t) 1);
        !            93:          wp[wsize] = cy;
        !            94:          wsize += cy;
        !            95:        }
        !            96:       else
        !            97:        {
        !            98:          /* We shifted something negative to zero.  The result is -1.  */
        !            99:          wp[0] = 1;
        !           100:          wsize = 1;
        !           101:        }
1.1       maekawa   102:     }
                    103:   w->_mp_size = usize >= 0 ? wsize : -wsize;
                    104: }