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Annotation of OpenXM/src/kan96xx/gmp-2.0.2/mpz/fdiv_q_2exp.c, Revision 1.1.1.1

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: }