1 files changed, 48 insertions, 0 deletions
diff --git a/lib/crypto/mpi/generic_mpih-mul3.c b/lib/crypto/mpi/generic_mpih-mul3.c
new file mode 100644
index 0000000000..ccdbab4121
--- /dev/null
+++ b/lib/crypto/mpi/generic_mpih-mul3.c
@@ -0,0 +1,48 @@
+// 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;
+}