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// SPDX-License-Identifier: GPL-2.0-or-later
/* mpihelp-mul_3.c - MPI helper functions
* Copyright (C) 1994, 1996, 1997, 1998, 2001 Free Software Foundation, Inc.
*
* This file is part of GnuPG.
*
* Note: This code is heavily based on the GNU MP Library.
* Actually it's the same code with only minor changes in the
* way the data is stored; this is to support the abstraction
* of an optional secure memory allocation which may be used
* to avoid revealing of sensitive data due to paging etc.
* The GNU MP Library itself is published under the LGPL;
* however I decided to publish this code under the plain GPL.
*/
#include "mpi-internal.h"
#include "longlong.h"
mpi_limb_t
mpihelp_submul_1(mpi_ptr_t res_ptr, mpi_ptr_t s1_ptr,
mpi_size_t s1_size, mpi_limb_t s2_limb)
{
mpi_limb_t cy_limb;
mpi_size_t j;
mpi_limb_t prod_high, prod_low;
mpi_limb_t x;
/* The loop counter and index J goes from -SIZE to -1. This way
* the loop becomes faster. */
j = -s1_size;
res_ptr -= j;
s1_ptr -= j;
cy_limb = 0;
do {
umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
prod_low += cy_limb;
cy_limb = (prod_low < cy_limb ? 1 : 0) + prod_high;
x = res_ptr[j];
prod_low = x - prod_low;
cy_limb += prod_low > x ? 1 : 0;
res_ptr[j] = prod_low;
} while (++j);
return cy_limb;
}
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