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107 lines
2.5 KiB
C
107 lines
2.5 KiB
C
/* mpihelp-sub.c - MPI helper functions
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* Copyright (c) 1997 by Werner Koch (dd9jn)
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*
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* This file is part of G10.
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*
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* G10 is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* G10 is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
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*/
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#include <config.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include "mpi-internal.h"
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/*_EXTERN_INLINE*/
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mpi_limb_t
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mpihelp_sub_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
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mpi_size_t s1_size, mpi_limb_t s2_limb )
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{
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mpi_limb_t x;
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x = *s1_ptr++;
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s2_limb = x - s2_limb;
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*res_ptr++ = s2_limb;
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if( s2_limb > x ) {
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while( --s1_size ) {
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x = *s1_ptr++;
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*res_ptr++ = x - 1;
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if( x )
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goto leave;
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}
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return 1;
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}
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leave:
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if( res_ptr != s1_ptr ) {
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mpi_size_t i;
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for( i=0; i < s1_size-1; i++ )
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res_ptr[i] = s1_ptr[i];
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}
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return 0;
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}
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/* FIXME: this should be done in assembly */
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mpi_limb_t
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mpihelp_sub_n( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
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mpi_ptr_t s2_ptr, mpi_size_t size)
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{
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mpi_limb_t x, y, cy;
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mpi_size_t j;
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/* The loop counter and index J goes from -SIZE to -1. This way
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the loop becomes faster. */
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j = -size;
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/* Offset the base pointers to compensate for the negative indices. */
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s1_ptr -= j;
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s2_ptr -= j;
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res_ptr -= j;
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cy = 0;
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do {
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y = s2_ptr[j];
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x = s1_ptr[j];
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y += cy; /* add previous carry to subtrahend */
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cy = y < cy ? 1:0; /* get out carry from that addition */
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y = x - y; /* main subtract */
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cy += y > x? 1:0; /* get out carry from the subtract, combine */
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res_ptr[j] = y;
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} while( ++j );
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return cy;
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}
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/*_EXTERN_INLINE*/
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mpi_limb_t
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mpihelp_sub( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
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mpi_ptr_t s2_ptr, mpi_size_t s2_size)
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{
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mpi_limb_t cy = 0;
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if( s2_size )
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cy = mpihelp_sub_n(res_ptr, s1_ptr, s2_ptr, s2_size);
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if( s1_size - s2_size )
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cy = mpihelp_sub_1(res_ptr + s2_size, s1_ptr + s2_size,
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s1_size - s2_size, cy);
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return cy;
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}
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