1/* mpn_sub_n -- Subtract two limb vectors of equal, non-zero length. 2 3Copyright (C) 1992, 1993, 1994, 1996 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 2.1 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; see the file COPYING.LIB. If not, write to 19the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, 20MA 02111-1307, USA. */ 21 22#include <config.h> 23#include "gmp-impl.h" 24 25mp_limb_t 26#if __STDC__ 27mpn_sub_n (mp_ptr res_ptr, mp_srcptr s1_ptr, mp_srcptr s2_ptr, mp_size_t size) 28#else 29mpn_sub_n (res_ptr, s1_ptr, s2_ptr, size) 30 register mp_ptr res_ptr; 31 register mp_srcptr s1_ptr; 32 register mp_srcptr s2_ptr; 33 mp_size_t size; 34#endif 35{ 36 register mp_limb_t x, y, cy; 37 register mp_size_t j; 38 39 /* The loop counter and index J goes from -SIZE to -1. This way 40 the loop becomes faster. */ 41 j = -size; 42 43 /* Offset the base pointers to compensate for the negative indices. */ 44 s1_ptr -= j; 45 s2_ptr -= j; 46 res_ptr -= j; 47 48 cy = 0; 49 do 50 { 51 y = s2_ptr[j]; 52 x = s1_ptr[j]; 53 y += cy; /* add previous carry to subtrahend */ 54 cy = (y < cy); /* get out carry from that addition */ 55 y = x - y; /* main subtract */ 56 cy = (y > x) + cy; /* get out carry from the subtract, combine */ 57 res_ptr[j] = y; 58 } 59 while (++j != 0); 60 61 return cy; 62} 63