xref: /netbsd-src/external/lgpl3/gmp/dist/mpz/cdiv_qr_ui.c (revision 4d342c046e3288fb5a1edcd33cfec48c41c80664)
1 /* mpz_cdiv_qr_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, 2012 Free Software Foundation,
7 Inc.
8 
9 This file is part of the GNU MP Library.
10 
11 The GNU MP Library is free software; you can redistribute it and/or modify
12 it under the terms of either:
13 
14   * the GNU Lesser General Public License as published by the Free
15     Software Foundation; either version 3 of the License, or (at your
16     option) any later version.
17 
18 or
19 
20   * the GNU General Public License as published by the Free Software
21     Foundation; either version 2 of the License, or (at your option) any
22     later version.
23 
24 or both in parallel, as here.
25 
26 The GNU MP Library is distributed in the hope that it will be useful, but
27 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
28 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
29 for more details.
30 
31 You should have received copies of the GNU General Public License and the
32 GNU Lesser General Public License along with the GNU MP Library.  If not,
33 see https://www.gnu.org/licenses/.  */
34 
35 #include "gmp.h"
36 #include "gmp-impl.h"
37 
38 unsigned long int
39 mpz_cdiv_qr_ui (mpz_ptr quot, mpz_ptr rem, mpz_srcptr dividend, unsigned long int divisor)
40 {
41   mp_size_t ns, nn, qn;
42   mp_ptr np, qp;
43   mp_limb_t rl;
44 
45   if (UNLIKELY (divisor == 0))
46     DIVIDE_BY_ZERO;
47 
48   ns = SIZ(dividend);
49   if (ns == 0)
50     {
51       SIZ(quot) = 0;
52       SIZ(rem) = 0;
53       return 0;
54     }
55 
56   nn = ABS(ns);
57   qp = MPZ_REALLOC (quot, nn);
58   np = PTR(dividend);
59 
60 #if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
61   if (divisor > GMP_NUMB_MAX)
62     {
63       mp_limb_t dp[2];
64       mp_ptr rp;
65       mp_size_t rn;
66 
67       rp = MPZ_REALLOC (rem, 2);
68 
69       if (nn == 1)		/* tdiv_qr requirements; tested above for 0 */
70 	{
71 	  qp[0] = 0;
72 	  qn = 1;		/* a white lie, fixed below */
73 	  rl = np[0];
74 	  rp[0] = rl;
75 	}
76       else
77 	{
78 	  dp[0] = divisor & GMP_NUMB_MASK;
79 	  dp[1] = divisor >> GMP_NUMB_BITS;
80 	  mpn_tdiv_qr (qp, rp, (mp_size_t) 0, np, nn, dp, (mp_size_t) 2);
81 	  rl = rp[0] + (rp[1] << GMP_NUMB_BITS);
82 	  qn = nn - 2 + 1;
83 	}
84 
85       if (rl != 0 && ns >= 0)
86 	{
87 	  mpn_incr_u (qp, (mp_limb_t) 1);
88 	  rl = divisor - rl;
89 	  rp[0] = rl & GMP_NUMB_MASK;
90 	  rp[1] = rl >> GMP_NUMB_BITS;
91 	}
92 
93       qn -= qp[qn - 1] == 0; qn -= qn != 0 && qp[qn - 1] == 0;
94       rn = 1 + (rl > GMP_NUMB_MAX);  rn -= (rp[rn - 1] == 0);
95       SIZ(rem) = -rn;
96     }
97   else
98 #endif
99     {
100       rl = mpn_divrem_1 (qp, (mp_size_t) 0, np, nn, (mp_limb_t) divisor);
101       if (rl == 0)
102 	SIZ(rem) = 0;
103       else
104 	{
105 	  if (ns >= 0)
106 	    {
107 	      mpn_incr_u (qp, (mp_limb_t) 1);
108 	      rl = divisor - rl;
109 	    }
110 
111 	  PTR(rem)[0] = rl;
112 	  SIZ(rem) = -(rl != 0);
113 	}
114       qn = nn - (qp[nn - 1] == 0);
115     }
116 
117   SIZ(quot) = ns >= 0 ? qn : -qn;
118   return rl;
119 }
120