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