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+// SPDX-License-Identifier: GPL-2.0-or-later
+/* mpihelp-mul_1.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_mul_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;
+
+ /* The loop counter and index J goes from -S1_SIZE to -1. This way
+ * the loop becomes faster. */
+ j = -s1_size;
+
+ /* Offset the base pointers to compensate for the negative indices. */
+ s1_ptr -= j;
+ res_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;
+ res_ptr[j] = prod_low;
+ } while (++j);
+
+ return cy_limb;
+}