contrib/gmp/mpz/cdiv_q_ui.c

   1 /* mpz_cdiv_q_ui -- Division rounding the quotient towards +infinity.  The
   2    remainder gets the opposite sign as the denominator.  In order to make it
   3    always fit into the return type, the negative of the true remainder is
   4    returned.
   5
   6 Copyright 1994, 1996, 1999, 2001, 2002, 2004 Free Software Foundation, Inc.
   7
   8 This file is part of the GNU MP Library.
   9
  10 The GNU MP Library is free software; you can redistribute it and/or modify
  11 it under the terms of the GNU Lesser General Public License as published by
  12 the Free Software Foundation; either version 3 of the License, or (at your
  13 option) any later version.
  14
  15 The GNU MP Library is distributed in the hope that it will be useful, but
  16 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  17 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  18 License for more details.
  19
  20 You should have received a copy of the GNU Lesser General Public License
  21 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  22
  23 #include "gmp.h"
  24 #include "gmp-impl.h"
  25
  26 unsigned long int
  27 mpz_cdiv_q_ui (mpz_ptr quot, mpz_srcptr dividend, unsigned long int divisor)
  28 {
  29   mp_size_t ns, nn, qn;
  30   mp_ptr np, qp;
  31   mp_limb_t rl;
  32
  33   if (divisor == 0)
  34     DIVIDE_BY_ZERO;
  35
  36   ns = SIZ(dividend);
  37   if (ns == 0)
  38     {
  39       SIZ(quot) = 0;
  40       return 0;
  41     }
  42
  43   nn = ABS(ns);
  44   MPZ_REALLOC (quot, nn);
  45   qp = PTR(quot);
  46   np = PTR(dividend);
  47
  48 #if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
  49   if (divisor > GMP_NUMB_MAX)
  50     {
  51       mp_limb_t dp[2], rp[2];
  52
  53       if (nn == 1)              /* tdiv_qr requirements; tested above for 0 */
  54         {
  55           qp[0] = 0;
  56           rl = np[0];
  57           qn = 1;               /* a white lie, fixed below */
  58         }
  59       else
  60         {
  61           dp[0] = divisor & GMP_NUMB_MASK;
  62           dp[1] = divisor >> GMP_NUMB_BITS;
  63           mpn_tdiv_qr (qp, rp, (mp_size_t) 0, np, nn, dp, (mp_size_t) 2);
  64           rl = rp[0] + (rp[1] << GMP_NUMB_BITS);
  65           qn = nn - 2 + 1;
  66         }
  67
  68       if (rl != 0 && ns >= 0)
  69         {
  70           mpn_incr_u (qp, (mp_limb_t) 1);
  71           rl = divisor - rl;
  72         }
  73
  74       qn -= qp[qn - 1] == 0; qn -= qn != 0 && qp[qn - 1] == 0;
  75     }
  76   else
  77 #endif
  78     {
  79       rl = mpn_divrem_1 (qp, (mp_size_t) 0, np, nn, (mp_limb_t) divisor);
  80
  81       if (rl != 0 && ns >= 0)
  82         {
  83           mpn_incr_u (qp, (mp_limb_t) 1);
  84           rl = divisor - rl;
  85         }
  86
  87       qn = nn - (qp[nn - 1] == 0);
  88     }
  89
  90   SIZ(quot) = ns >= 0 ? qn : -qn;
  91   return rl;
  92 }