1/* mpz_ui_sub -- Subtract an unsigned one-word integer and an mpz_t.
2
3Copyright 2002, 2004 Free Software Foundation, Inc.
4
5This file is part of the GNU MP Library.
6
7The GNU MP Library is free software; you can redistribute it and/or modify
8it under the terms of the GNU Lesser General Public License as published by
9the Free Software Foundation; either version 3 of the License, or (at your
10option) any later version.
11
12The GNU MP Library is distributed in the hope that it will be useful, but
13WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
14or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
15License for more details.
16
17You should have received a copy of the GNU Lesser General Public License
18along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
19
20#include "gmp.h"
21#include "gmp-impl.h"
22
23void
24mpz_ui_sub (mpz_ptr w, unsigned long int uval, mpz_srcptr v)
25{
26  mp_ptr vp, wp;
27  mp_size_t vn, wn;
28  mp_limb_t cy;
29
30#if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
31  if (uval > GMP_NUMB_MAX)
32    {
33      mpz_t u;
34      mp_limb_t ul[2];
35      PTR(u) = ul;
36      ul[0] = uval & GMP_NUMB_MASK;
37      ul[1] = uval >> GMP_NUMB_BITS;
38      SIZ(u) = 2;
39      mpz_sub (w, u, v);
40      return;
41    }
42#endif
43
44  vp = PTR(v);
45  vn = SIZ(v);
46
47  wp = PTR(w);
48
49  if (vn > 1)
50    {
51      wp = MPZ_REALLOC (w, vn);
52      vp = PTR(v);
53      mpn_sub_1 (wp, vp, vn, (mp_limb_t) uval);
54      wn = -(vn - (wp[vn - 1] == 0));
55    }
56  else if (vn == 1)
57    {
58      if (uval >= vp[0])
59	{
60	  wp[0] = uval - vp[0];
61	  wn = wp[0] != 0;
62	}
63      else
64	{
65	  wp[0] = vp[0] - uval;
66	  wn = -1;
67	}
68    }
69  else if (vn == 0)
70    {
71      wp[0] = uval;
72      wn = uval != 0;
73    }
74  else /* (vn < 0) */
75    {
76      vn = -vn;
77      wp = MPZ_REALLOC (w, vn + 1);
78      vp = PTR(v);
79      cy = mpn_add_1 (wp, vp, vn, (mp_limb_t) uval);
80      wp[vn] = cy;
81      wn = vn + (cy != 0);
82    }
83
84  SIZ(w) = wn;
85}
86