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fdiv_qr_ui.c revision 1.1.1.3 
      1 /* mpz_fdiv_qr_ui -- Division rounding the quotient towards -infinity.
      2    The remainder gets the same sign as the denominator.
      3 
      4 Copyright 1994-1996, 1999, 2001, 2002, 2004, 2012 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 either:
     11 
     12   * the GNU Lesser General Public License as published by the Free
     13     Software Foundation; either version 3 of the License, or (at your
     14     option) any later version.
     15 
     16 or
     17 
     18   * the GNU General Public License as published by the Free Software
     19     Foundation; either version 2 of the License, or (at your option) any
     20     later version.
     21 
     22 or both in parallel, as here.
     23 
     24 The GNU MP Library is distributed in the hope that it will be useful, but
     25 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     26 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     27 for more details.
     28 
     29 You should have received copies of the GNU General Public License and the
     30 GNU Lesser General Public License along with the GNU MP Library.  If not,
     31 see https://www.gnu.org/licenses/.  */
     32 
     33 #include "gmp.h"
     34 #include "gmp-impl.h"
     35 
     36 unsigned long int
     37 mpz_fdiv_qr_ui (mpz_ptr quot, mpz_ptr rem, mpz_srcptr dividend, unsigned long int divisor)
     38 {
     39   mp_size_t ns, nn, qn;
     40   mp_ptr np, qp;
     41   mp_limb_t rl;
     42 
     43   if (UNLIKELY (divisor == 0))
     44     DIVIDE_BY_ZERO;
     45 
     46   ns = SIZ(dividend);
     47   if (ns == 0)
     48     {
     49       SIZ(quot) = 0;
     50       SIZ(rem) = 0;
     51       return 0;
     52     }
     53 
     54   nn = ABS(ns);
     55   qp = MPZ_REALLOC (quot, nn);
     56   np = PTR(dividend);
     57 
     58 #if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
     59   if (divisor > GMP_NUMB_MAX)
     60     {
     61       mp_limb_t dp[2];
     62       mp_ptr rp;
     63       mp_size_t rn;
     64 
     65       MPZ_REALLOC (rem, 2);
     66       rp = PTR(rem);
     67 
     68       if (nn == 1)		/* tdiv_qr requirements; tested above for 0 */
     69 	{
     70 	  qp[0] = 0;
     71 	  qn = 1;		/* a white lie, fixed below */
     72 	  rl = np[0];
     73 	  rp[0] = rl;
     74 	}
     75       else
     76 	{
     77 	  dp[0] = divisor & GMP_NUMB_MASK;
     78 	  dp[1] = divisor >> GMP_NUMB_BITS;
     79 	  mpn_tdiv_qr (qp, rp, (mp_size_t) 0, np, nn, dp, (mp_size_t) 2);
     80 	  rl = rp[0] + (rp[1] << GMP_NUMB_BITS);
     81 	  qn = nn - 2 + 1;
     82 	}
     83 
     84       if (rl != 0 && ns < 0)
     85 	{
     86 	  mpn_incr_u (qp, (mp_limb_t) 1);
     87 	  rl = divisor - rl;
     88 	  rp[0] = rl & GMP_NUMB_MASK;
     89 	  rp[1] = rl >> GMP_NUMB_BITS;
     90 	}
     91 
     92       qn -= qp[qn - 1] == 0; qn -= qn != 0 && qp[qn - 1] == 0;
     93       rn = 1 + (rl > GMP_NUMB_MAX);  rn -= (rp[rn - 1] == 0);
     94       SIZ(rem) = rn;
     95     }
     96   else
     97 #endif
     98     {
     99       rl = mpn_divrem_1 (qp, (mp_size_t) 0, np, nn, (mp_limb_t) divisor);
    100       if (rl == 0)
    101 	SIZ(rem) = 0;
    102       else
    103 	{
    104 	  if (ns < 0)
    105 	    {
    106 	      mpn_incr_u (qp, (mp_limb_t) 1);
    107 	      rl = divisor - rl;
    108 	    }
    109 
    110 	  PTR(rem)[0] = rl;
    111 	  SIZ(rem) = rl != 0;
    112 	}
    113       qn = nn - (qp[nn - 1] == 0);
    114     }
    115 
    116   SIZ(quot) = ns >= 0 ? qn : -qn;
    117   return rl;
    118 }
    119