contrib/gmp/mpz/cfdiv_q_2exp.c

   1 /* mpz_cdiv_q_2exp, mpz_fdiv_q_2exp -- quotient from mpz divided by 2^n.
   2
   3 Copyright 1991, 1993, 1994, 1996, 1998, 1999, 2001, 2002, 2004 Free Software
   4 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 Lesser General Public License as published by
  10 the Free Software Foundation; either version 3 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 Lesser General Public
  16 License for more details.
  17
  18 You should have received a copy of the GNU Lesser General Public License
  19 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  20
  21 #include "gmp.h"
  22 #include "gmp-impl.h"
  23
  24
  25 /* dir==1 for ceil, dir==-1 for floor */
  26
  27 static void __gmpz_cfdiv_q_2exp __GMP_PROTO ((REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int))) REGPARM_ATTR (1);
  28 #define cfdiv_q_2exp(w,u,cnt,dir)  __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir))
  29
  30 REGPARM_ATTR (1) static void
  31 cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
  32 {
  33   mp_size_t  wsize, usize, abs_usize, limb_cnt, i;
  34   mp_srcptr  up;
  35   mp_ptr     wp;
  36   mp_limb_t  round, rmask;
  37
  38   usize = SIZ (u);
  39   abs_usize = ABS (usize);
  40   limb_cnt = cnt / GMP_NUMB_BITS;
  41   wsize = abs_usize - limb_cnt;
  42   if (wsize <= 0)
  43     {
  44       /* u < 2**cnt, so result 1, 0 or -1 according to rounding */
  45       PTR(w)[0] = 1;
  46       SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir);
  47       return;
  48     }
  49
  50   /* +1 limb to allow for mpn_add_1 below */
  51   MPZ_REALLOC (w, wsize+1);
  52
  53   /* Check for rounding if direction matches u sign.
  54      Set round if we're skipping non-zero limbs.  */
  55   up = PTR(u);
  56   round = 0;
  57   rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0);
  58   if (rmask != 0)
  59     for (i = 0; i < limb_cnt && round == 0; i++)
  60       round = up[i];
  61
  62   wp = PTR(w);
  63   cnt %= GMP_NUMB_BITS;
  64   if (cnt != 0)
  65     {
  66       round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt);
  67       wsize -= (wp[wsize - 1] == 0);
  68     }
  69   else
  70     MPN_COPY_INCR (wp, up + limb_cnt, wsize);
  71
  72   if (round != 0)
  73     {
  74       if (wsize != 0)
  75         {
  76           mp_limb_t cy;
  77           cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
  78           wp[wsize] = cy;
  79           wsize += cy;
  80         }
  81       else
  82         {
  83           /* We shifted something to zero.  */
  84           wp[0] = 1;
  85           wsize = 1;
  86         }
  87     }
  88   SIZ(w) = (usize >= 0 ? wsize : -wsize);
  89 }
  90
  91
  92 void
  93 mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
  94 {
  95   cfdiv_q_2exp (w, u, cnt, 1);
  96 }
  97
  98 void
  99 mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
 100 {
 101   cfdiv_q_2exp (w, u, cnt, -1);
 102 }