1 files changed, 107 insertions, 0 deletions
diff --git a/third_party/bearssl/src/i32_decred.c b/third_party/bearssl/src/i32_decred.c
new file mode 100644
index 0000000..dc476db
--- /dev/null
+++ b/third_party/bearssl/src/i32_decred.c
@@ -0,0 +1,107 @@
+/*
+ * 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_i32_decode_reduce(uint32_t *x,
+	const void *src, size_t len, const uint32_t *m)
+{
+	uint32_t m_bitlen;
+	size_t mblen, k, q;
+	const unsigned char *buf;
+
+	m_bitlen = m[0];
+
+	/*
+	 * Special case for an invalid modulus.
+	 */
+	if (m_bitlen == 0) {
+		x[0] = 0;
+		return;
+	}
+
+	/*
+	 * Clear the destination.
+	 */
+	br_i32_zero(x, m_bitlen);
+
+	/*
+	 * First decode directly as many bytes as possible without
+	 * reduction, taking care to leave a number of bytes which
+	 * is a multiple of 4.
+	 */
+	mblen = (m_bitlen + 7) >> 3;
+	k = mblen - 1;
+
+	/*
+	 * Up to k bytes can be safely decoded.
+	 */
+	if (k >= len) {
+		br_i32_decode(x, src, len);
+		x[0] = m_bitlen;
+		return;
+	}
+
+	/*
+	 * We want to first inject some bytes with direct decoding,
+	 * then extra bytes by whole 32-bit words. First compute
+	 * the size that should be injected that way.
+	 */
+	buf = src;
+	q = (len - k + 3) & ~(size_t)3;
+
+	/*
+	 * It may happen that this is more than what we already have
+	 * (by at most 3 bytes). Such a case may happen only with
+	 * a very short modulus. In that case, we must process the first
+	 * bytes "manually".
+	 */
+	if (q > len) {
+		int i;
+		uint32_t w;
+
+		w = 0;
+		for (i = 0; i < 4; i ++) {
+			w <<= 8;
+			if (q <= len) {
+				w |= buf[len - q];
+			}
+			q --;
+		}
+		br_i32_muladd_small(x, w, m);
+	} else {
+		br_i32_decode(x, buf, len - q);
+		x[0] = m_bitlen;
+	}
+
+	/*
+	 * At that point, we have exactly q bytes to inject, and q is
+	 * a multiple of 4.
+	 */
+	for (k = len - q; k < len; k += 4) {
+		br_i32_muladd_small(x, br_dec32be(buf + k), m);
+	}
+}