source/libs/gmp/gmp-src/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, 2012,
   4 2015 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 either:
  10
  11   * the GNU Lesser General Public License as published by the Free
  12     Software Foundation; either version 3 of the License, or (at your
  13     option) any later version.
  14
  15 or
  16
  17   * the GNU General Public License as published by the Free Software
  18     Foundation; either version 2 of the License, or (at your option) any
  19     later version.
  20
  21 or both in parallel, as here.
  22
  23 The GNU MP Library is distributed in the hope that it will be useful, but
  24 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  25 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  26 for more details.
  27
  28 You should have received copies of the GNU General Public License and the
  29 GNU Lesser General Public License along with the GNU MP Library.  If not,
  30 see https://www.gnu.org/licenses/.  */
  31
  32 #include "gmp.h"
  33 #include "gmp-impl.h"
  34
  35
  36 /* dir==1 for ceil, dir==-1 for floor */
  37
  38 static void __gmpz_cfdiv_q_2exp (REGPARM_3_1 (mpz_ptr, mpz_srcptr, mp_bitcnt_t, int)) REGPARM_ATTR (1);
  39 #define cfdiv_q_2exp(w,u,cnt,dir)  __gmpz_cfdiv_q_2exp (REGPARM_3_1 (w,u,cnt,dir))
  40
  41 REGPARM_ATTR (1) static void
  42 cfdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt, int dir)
  43 {
  44   mp_size_t  wsize, usize, abs_usize, limb_cnt, i;
  45   mp_srcptr  up;
  46   mp_ptr     wp;
  47   mp_limb_t  round, rmask;
  48
  49   usize = SIZ (u);
  50   abs_usize = ABS (usize);
  51   limb_cnt = cnt / GMP_NUMB_BITS;
  52   wsize = abs_usize - limb_cnt;
  53   if (wsize <= 0)
  54     {
  55       /* u < 2**cnt, so result 1, 0 or -1 according to rounding */
  56       PTR(w)[0] = 1;
  57       SIZ(w) = (usize == 0 || (usize ^ dir) < 0 ? 0 : dir);
  58       return;
  59     }
  60
  61   /* +1 limb to allow for mpn_add_1 below */
  62   wp = MPZ_REALLOC (w, wsize+1);
  63
  64   /* Check for rounding if direction matches u sign.
  65      Set round if we're skipping non-zero limbs.  */
  66   up = PTR(u);
  67   round = 0;
  68   rmask = ((usize ^ dir) >= 0 ? MP_LIMB_T_MAX : 0);
  69   if (rmask != 0)
  70     for (i = 0; i < limb_cnt && round == 0; i++)
  71       round = up[i];
  72
  73   cnt %= GMP_NUMB_BITS;
  74   if (cnt != 0)
  75     {
  76       round |= rmask & mpn_rshift (wp, up + limb_cnt, wsize, cnt);
  77       wsize -= (wp[wsize - 1] == 0);
  78     }
  79   else
  80     MPN_COPY_INCR (wp, up + limb_cnt, wsize);
  81
  82   if (round != 0)
  83     {
  84       if (wsize != 0)
  85         {
  86           mp_limb_t cy;
  87           cy = mpn_add_1 (wp, wp, wsize, CNST_LIMB(1));
  88           wp[wsize] = cy;
  89           wsize += cy;
  90         }
  91       else
  92         {
  93           /* We shifted something to zero.  */
  94           wp[0] = 1;
  95           wsize = 1;
  96         }
  97     }
  98   SIZ(w) = (usize >= 0 ? wsize : -wsize);
  99 }
 100
 101
 102 void
 103 mpz_cdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
 104 {
 105   cfdiv_q_2exp (w, u, cnt, 1);
 106 }
 107
 108 void
 109 mpz_fdiv_q_2exp (mpz_ptr w, mpz_srcptr u, mp_bitcnt_t cnt)
 110 {
 111   cfdiv_q_2exp (w, u, cnt, -1);
 112 }