contrib/gmp/mpz/fdiv_qr_ui.c

   1 /* mpz_fdiv_qr_ui -- Division rounding the quotient towards -infinity.
   2    The remainder gets the same sign as the denominator.
   3
   4 Copyright 1994, 1995, 1996, 1999, 2001, 2002, 2004 Free Software Foundation,
   5 Inc.
   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
  10 it under the terms of the GNU Lesser General Public License as published by
  11 the Free Software Foundation; either version 3 of the License, or (at your
  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
  16 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  17 License for more details.
  18
  19 You should have received a copy of the GNU Lesser General Public License
  20 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  21
  22 #include "gmp.h"
  23 #include "gmp-impl.h"
  24
  25 unsigned long int
  26 mpz_fdiv_qr_ui (mpz_ptr quot, mpz_ptr rem, mpz_srcptr dividend, unsigned long int divisor)
  27 {
  28   mp_size_t ns, nn, qn;
  29   mp_ptr np, qp;
  30   mp_limb_t rl;
  31
  32   if (divisor == 0)
  33     DIVIDE_BY_ZERO;
  34
  35   ns = SIZ(dividend);
  36   if (ns == 0)
  37     {
  38       SIZ(quot) = 0;
  39       SIZ(rem) = 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];
  52       mp_ptr rp;
  53       mp_size_t rn;
  54
  55       MPZ_REALLOC (rem, 2);
  56       rp = PTR(rem);
  57
  58       if (nn == 1)              /* tdiv_qr requirements; tested above for 0 */
  59         {
  60           qp[0] = 0;
  61           qn = 1;               /* a white lie, fixed below */
  62           rl = np[0];
  63           rp[0] = rl;
  64         }
  65       else
  66         {
  67           dp[0] = divisor & GMP_NUMB_MASK;
  68           dp[1] = divisor >> GMP_NUMB_BITS;
  69           mpn_tdiv_qr (qp, rp, (mp_size_t) 0, np, nn, dp, (mp_size_t) 2);
  70           rl = rp[0] + (rp[1] << GMP_NUMB_BITS);
  71           qn = nn - 2 + 1;
  72         }
  73
  74       if (rl != 0 && ns < 0)
  75         {
  76           mpn_incr_u (qp, (mp_limb_t) 1);
  77           rl = divisor - rl;
  78           rp[0] = rl & GMP_NUMB_MASK;
  79           rp[1] = rl >> GMP_NUMB_BITS;
  80         }
  81
  82       qn -= qp[qn - 1] == 0; qn -= qn != 0 && qp[qn - 1] == 0;
  83       rn = 1 + (rl > GMP_NUMB_MAX);  rn -= (rp[rn - 1] == 0);
  84       SIZ(rem) = rn;
  85     }
  86   else
  87 #endif
  88     {
  89       rl = mpn_divrem_1 (qp, (mp_size_t) 0, np, nn, (mp_limb_t) divisor);
  90       if (rl == 0)
  91         SIZ(rem) = 0;
  92       else
  93         {
  94           if (ns < 0)
  95             {
  96               mpn_incr_u (qp, (mp_limb_t) 1);
  97               rl = divisor - rl;
  98             }
  99
 100           PTR(rem)[0] = rl;
 101           SIZ(rem) = rl != 0;
 102         }
 103       qn = nn - (qp[nn - 1] == 0);
 104     }
 105
 106   SIZ(quot) = ns >= 0 ? qn : -qn;
 107   return rl;
 108 }