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+/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length.
+
+Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
+
+This file is part of the GNU MP Library.
+
+The GNU MP Library is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or (at your
+option) any later version.
+
+The GNU MP Library is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with the GNU MP Library; see the file COPYING.LIB. If not, write to
+the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+MA 02111-1307, USA. */
+
+#include "gmp.h"
+#include "gmp-impl.h"
+
+mp_limb_t
+#if __STDC__
+mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size)
+#else
+mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size)
+ register mp_ptr res_ptr;
+ register mp_srcptr s1_ptr;
+ register mp_srcptr s2_ptr;
+ mp_size_t size;
+#endif
+{
+ register mp_limb_t x, y, cy;
+ register mp_size_t j;
+
+ /* The loop counter and index J goes from -SIZE to -1. This way
+ the loop becomes faster. */
+ j = -size;
+
+ /* Offset the base pointers to compensate for the negative indices. */
+ s1_ptr -= j;
+ s2_ptr -= j;
+ res_ptr -= j;
+
+ cy = 0;
+ do
+ {
+ y = s2_ptr[j];
+ x = s1_ptr[j];
+ y += cy; /* add previous carry to subtrahend */
+ cy = (y < cy); /* get out carry from that addition */
+ y = x - y; /* main subtract */
+ cy = (y > x) + cy; /* get out carry from the subtract, combine */
+ res_ptr[j] = y;
+ }
+ while (++j != 0);
+
+ return cy;
+}