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ui_sub.c revision 1.1.1.3 
      1 /* mpz_ui_sub -- Subtract an unsigned one-word integer and an mpz_t.
      2 
      3 Copyright 2002, 2004, 2015 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 either:
      9 
     10   * the GNU Lesser General Public License as published by the Free
     11     Software Foundation; either version 3 of the License, or (at your
     12     option) any later version.
     13 
     14 or
     15 
     16   * the GNU General Public License as published by the Free Software
     17     Foundation; either version 2 of the License, or (at your option) any
     18     later version.
     19 
     20 or both in parallel, as here.
     21 
     22 The GNU MP Library is distributed in the hope that it will be useful, but
     23 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
     24 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
     25 for more details.
     26 
     27 You should have received copies of the GNU General Public License and the
     28 GNU Lesser General Public License along with the GNU MP Library.  If not,
     29 see https://www.gnu.org/licenses/.  */
     30 
     31 #include "gmp-impl.h"
     32 
     33 void
     34 mpz_ui_sub (mpz_ptr w, unsigned long int uval, mpz_srcptr v)
     35 {
     36   mp_ptr vp, wp;
     37   mp_size_t vn, wn;
     38   mp_limb_t cy;
     39 
     40 #if BITS_PER_ULONG > GMP_NUMB_BITS  /* avoid warnings about shift amount */
     41   if (uval > GMP_NUMB_MAX)
     42     {
     43       mpz_t u;
     44       mp_limb_t ul[2];
     45       PTR(u) = ul;
     46       ul[0] = uval & GMP_NUMB_MASK;
     47       ul[1] = uval >> GMP_NUMB_BITS;
     48       SIZ(u) = 2;
     49       mpz_sub (w, u, v);
     50       return;
     51     }
     52 #endif
     53 
     54   vn = SIZ(v);
     55 
     56   if (vn > 1)
     57     {
     58       wp = MPZ_REALLOC (w, vn);
     59       vp = PTR(v);
     60       mpn_sub_1 (wp, vp, vn, (mp_limb_t) uval);
     61       wn = -(vn - (wp[vn - 1] == 0));
     62     }
     63   else if (vn >= 0)
     64     {
     65       mp_limb_t vp0;
     66       vp0 = PTR (v)[0] & - (mp_limb_t) vn;
     67       wp = MPZ_NEWALLOC (w, 1);
     68       if (uval >= vp0)
     69 	{
     70 	  wp[0] = uval - vp0;
     71 	  wn = wp[0] != 0;
     72 	}
     73       else
     74 	{
     75 	  wp[0] = vp0 - uval;
     76 	  wn = -1;
     77 	}
     78     }
     79   else /* (vn < 0) */
     80     {
     81       vn = -vn;
     82       wp = MPZ_REALLOC (w, vn + 1);
     83       vp = PTR(v);
     84       cy = mpn_add_1 (wp, vp, vn, (mp_limb_t) uval);
     85       wp[vn] = cy;
     86       wn = vn + (cy != 0);
     87     }
     88 
     89   SIZ(w) = wn;
     90 }
     91