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Annotation of OpenXM_contrib/gmp/mpn/generic/submul_1.c, Revision 1.1.1.1

1.1       maekawa     1: /* mpn_submul_1 -- multiply the S1_SIZE long limb vector pointed to by S1_PTR
                      2:    by S2_LIMB, subtract the S1_SIZE least significant limbs of the product
                      3:    from the limb vector pointed to by RES_PTR.  Return the most significant
                      4:    limb of the product, adjusted for carry-out from the subtraction.
                      5:
                      6: Copyright (C) 1992, 1993, 1994, 1996 Free Software Foundation, Inc.
                      7:
                      8: This file is part of the GNU MP Library.
                      9:
                     10: The GNU MP Library is free software; you can redistribute it and/or modify
                     11: it under the terms of the GNU Library General Public License as published by
                     12: the Free Software Foundation; either version 2 of the License, or (at your
                     13: option) any later version.
                     14:
                     15: The GNU MP Library is distributed in the hope that it will be useful, but
                     16: WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
                     17: or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
                     18: License for more details.
                     19:
                     20: You should have received a copy of the GNU Library General Public License
                     21: along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
                     22: the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
                     23: MA 02111-1307, USA. */
                     24:
                     25: #include "gmp.h"
                     26: #include "gmp-impl.h"
                     27: #include "longlong.h"
                     28:
                     29: mp_limb_t
                     30: mpn_submul_1 (res_ptr, s1_ptr, s1_size, s2_limb)
                     31:      register mp_ptr res_ptr;
                     32:      register mp_srcptr s1_ptr;
                     33:      mp_size_t s1_size;
                     34:      register mp_limb_t s2_limb;
                     35: {
                     36:   register mp_limb_t cy_limb;
                     37:   register mp_size_t j;
                     38:   register mp_limb_t prod_high, prod_low;
                     39:   register mp_limb_t x;
                     40:
                     41:   /* The loop counter and index J goes from -SIZE to -1.  This way
                     42:      the loop becomes faster.  */
                     43:   j = -s1_size;
                     44:
                     45:   /* Offset the base pointers to compensate for the negative indices.  */
                     46:   res_ptr -= j;
                     47:   s1_ptr -= j;
                     48:
                     49:   cy_limb = 0;
                     50:   do
                     51:     {
                     52:       umul_ppmm (prod_high, prod_low, s1_ptr[j], s2_limb);
                     53:
                     54:       prod_low += cy_limb;
                     55:       cy_limb = (prod_low < cy_limb) + prod_high;
                     56:
                     57:       x = res_ptr[j];
                     58:       prod_low = x - prod_low;
                     59:       cy_limb += (prod_low > x);
                     60:       res_ptr[j] = prod_low;
                     61:     }
                     62:   while (++j != 0);
                     63:
                     64:   return cy_limb;
                     65: }