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glibc  2.9
submul_1.c
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00001 /* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR
00002    by S2_LIMB, subtract the S1_SIZE least significant limbs of the product
00003    from the limb vector pointed to by RES_PTR.  Return the most significant
00004    limb of the product, adjusted for carry-out from the subtraction.
00005 
00006 Copyright (C) 1992, 1993, 1994, 1996, 2005 Free Software Foundation, Inc.
00007 
00008 This file is part of the GNU MP Library.
00009 
00010 The GNU MP Library is free software; you can redistribute it and/or modify
00011 it under the terms of the GNU Lesser General Public License as published by
00012 the Free Software Foundation; either version 2.1 of the License, or (at your
00013 option) any later version.
00014 
00015 The GNU MP Library is distributed in the hope that it will be useful, but
00016 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
00017 or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
00018 License for more details.
00019 
00020 You should have received a copy of the GNU Lesser General Public License
00021 along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
00022 the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
00023 MA 02111-1307, USA. */
00024 
00025 #include <gmp.h>
00026 #include "gmp-impl.h"
00027 #include "longlong.h"
00028 
00029 mp_limb_t
00030 mpn_submul_1 (res_ptr, s1_ptr, s1_size, s2_limb)
00031      register mp_ptr res_ptr;
00032      register mp_srcptr s1_ptr;
00033      mp_size_t s1_size;
00034      register mp_limb_t s2_limb;
00035 {
00036   register mp_limb_t cy_limb;
00037   register mp_size_t j;
00038   register mp_limb_t prod_high, prod_low;
00039   register mp_limb_t x;
00040 
00041   /* The loop counter and index J goes from -SIZE to -1.  This way
00042      the loop becomes faster.  */
00043   j = -s1_size;
00044 
00045   /* Offset the base pointers to compensate for the negative indices.  */
00046   res_ptr -= j;
00047   s1_ptr -= j;
00048 
00049   cy_limb = 0;
00050   do
00051     {
00052       umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb);
00053 
00054       prod_low += cy_limb;
00055       cy_limb = (prod_low < cy_limb) + prod_high;
00056 
00057       x = res_ptr[j];
00058       prod_low = x - prod_low;
00059       cy_limb += (prod_low > x);
00060       res_ptr[j] = prod_low;
00061     }
00062   while (++j != 0);
00063 
00064   return cy_limb;
00065 }