1 files changed, 42 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_setup.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_setup.c
new file mode 100644
index 0000000..39f6e9d
--- /dev/null
+++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_mp_montgomery_setup.c
@@ -0,0 +1,42 @@
+#include "tommath_private.h"
+#ifdef BN_MP_MONTGOMERY_SETUP_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* setups the montgomery reduction stuff */
+mp_err mp_montgomery_setup(const mp_int *n, mp_digit *rho)
+{
+   mp_digit x, b;
+
+   /* fast inversion mod 2**k
+    *
+    * Based on the fact that
+    *
+    * XA = 1 (mod 2**n)  =>  (X(2-XA)) A = 1 (mod 2**2n)
+    *                    =>  2*X*A - X*X*A*A = 1
+    *                    =>  2*(1) - (1)     = 1
+    */
+   b = n->dp[0];
+
+   if ((b & 1u) == 0u) {
+      return MP_VAL;
+   }
+
+   x = (((b + 2u) & 4u) << 1) + b; /* here x*a==1 mod 2**4 */
+   x *= 2u - (b * x);              /* here x*a==1 mod 2**8 */
+#if !defined(MP_8BIT)
+   x *= 2u - (b * x);              /* here x*a==1 mod 2**16 */
+#endif
+#if defined(MP_64BIT) || !(defined(MP_8BIT) || defined(MP_16BIT))
+   x *= 2u - (b * x);              /* here x*a==1 mod 2**32 */
+#endif
+#ifdef MP_64BIT
+   x *= 2u - (b * x);              /* here x*a==1 mod 2**64 */
+#endif
+
+   /* rho = -1/m mod b */
+   *rho = (mp_digit)(((mp_word)1 << (mp_word)MP_DIGIT_BIT) - x) & MP_MASK;
+
+   return MP_OKAY;
+}
+#endif