1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/bearssl/src/i31_modpow.c b/third_party/bearssl/src/i31_modpow.c
new file mode 100644
index 0000000..4ef3f5d
--- /dev/null
+++ b/third_party/bearssl/src/i31_modpow.c
@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2016 Thomas Pornin <[email protected]>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining 
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be 
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#include "inner.h"
+
+/* see inner.h */
+void
+br_i31_modpow(uint32_t *x,
+	const unsigned char *e, size_t elen,
+	const uint32_t *m, uint32_t m0i, uint32_t *t1, uint32_t *t2)
+{
+	size_t mlen;
+	uint32_t k;
+
+	/*
+	 * 'mlen' is the length of m[] expressed in bytes (including
+	 * the "bit length" first field).
+	 */
+	mlen = ((m[0] + 63) >> 5) * sizeof m[0];
+
+	/*
+	 * Throughout the algorithm:
+	 * -- t1[] is in Montgomery representation; it contains x, x^2,
+	 * x^4, x^8...
+	 * -- The result is accumulated, in normal representation, in
+	 * the x[] array.
+	 * -- t2[] is used as destination buffer for each multiplication.
+	 *
+	 * Note that there is no need to call br_i32_from_monty().
+	 */
+	memcpy(t1, x, mlen);
+	br_i31_to_monty(t1, m);
+	br_i31_zero(x, m[0]);
+	x[1] = 1;
+	for (k = 0; k < ((uint32_t)elen << 3); k ++) {
+		uint32_t ctl;
+
+		ctl = (e[elen - 1 - (k >> 3)] >> (k & 7)) & 1;
+		br_i31_montymul(t2, x, t1, m, m0i);
+		CCOPY(ctl, x, t2, mlen);
+		br_i31_montymul(t2, t1, t1, m, m0i);
+		memcpy(t1, t2, mlen);
+	}
+}