contrib/gmp/mpz/ui_sub.c

   1 /* mpz_ui_sub -- Subtract an unsigned one-word integer and an mpz_t.
   2
   3 Copyright 2002, 2004 Free Software Foundation, Inc.
   4
   5 This file is part of the GNU MP Library.
   6
   7 The GNU MP Library is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU Lesser General Public License as published by
   9 the Free Software Foundation; either version 3 of the License, or (at your
  10 option) any later version.
  11
  12 The GNU MP Library is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  14 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
  15 License for more details.
  16
  17 You should have received a copy of the GNU Lesser General Public License
  18 along with the GNU MP Library.  If not, see http://www.gnu.org/licenses/.  */
  19
  20 #include "gmp.h"
  21 #include "gmp-impl.h"
  22
  23 void
  24 mpz_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 }