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/* mpihelp-add.c - MPI helper functions
* Copyright (c) 1997 by Werner Koch (dd9jn)
*
* This file is part of G10.
*
* G10 is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* G10 is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include "mpi-internal.h"
/****************
* Add to S1_PTR with size S1_SIZE the limb S2_LIMB and
* store the result in RES_PTR. Return the carry
* S1_SIZE must be > 0.
*/
/*_EXTERN_INLINE */
mpi_limb_t
mpihelp_add_1( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
mpi_size_t s1_size, mpi_limb_t s2_limb)
{
mpi_limb_t x;
x = *s1_ptr++;
s2_limb += x;
*res_ptr++ = s2_limb;
if( s2_limb < x ) { /* sum is less than the left operand: handle carry */
while( --s1_size ) {
x = *s1_ptr++ + 1; /* add carry */
*res_ptr++ = x; /* and store */
if( x ) /* not 0 (no overflow): we can stop */
goto leave;
}
return 1; /* return carry (size of s1 to small) */
}
leave:
if( res_ptr != s1_ptr ) { /* not the same variable */
mpi_size_t i; /* copy the rest */
for( i=0; i < s1_size-1; i++ )
res_ptr[i] = s1_ptr[i];
}
return 0; /* no carry */
}
/* FIXME: this should be done in assembly */
mpi_limb_t
mpihelp_add_n( mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
mpi_ptr_t s2_ptr, mpi_size_t size)
{
mpi_limb_t x, y, cy;
mpi_size_t j;
/* The loop counter and index J goes from -SIZE to -1. This way
the loop becomes faster. */
j = -size;
/* Offset the base pointers to compensate for the negative indices. */
s1_ptr -= j;
s2_ptr -= j;
res_ptr -= j;
cy = 0;
do {
y = s2_ptr[j];
x = s1_ptr[j];
y += cy; /* add previous carry to one addend */
cy = y < cy? 1:0; /* get out carry from that addition */
y += x; /* add other addend */
cy += y < x? 1:0; /* get out carry from that add, combine */
res_ptr[j] = y;
} while( ++j );
return cy;
}
/*_EXTERN_INLINE*/
mpi_limb_t
mpihelp_add(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr, mpi_size_t s1_size,
mpi_ptr_t s2_ptr, mpi_size_t s2_size)
{
mpi_limb_t cy = 0;
if( s2_size )
cy = mpihelp_add_n( res_ptr, s1_ptr, s2_ptr, s2_size );
if( s1_size - s2_size )
cy = mpihelp_add_1( res_ptr + s2_size, s1_ptr + s2_size,
s1_size - s2_size, cy);
return cy;
}
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