X-Git-Url: https://www.bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fint%2Fi15_decred.c;fp=src%2Fint%2Fi15_decred.c;h=81e7dd1bd7e98f5cc5dd8849a76993e67a0291fd;hp=0000000000000000000000000000000000000000;hb=2f454aad577ae53798935cc32438a2d3f02ba31f;hpb=bd3036844bd20b2b8d7bce7fee5ad010ce401915

diff --git a/src/int/i15_decred.c b/src/int/i15_decred.c
new file mode 100644
index 0000000..81e7dd1
--- /dev/null
+++ b/src/int/i15_decred.c
@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
+ *
+ * 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_i15_decode_reduce(uint16_t *x,
+	const void *src, size_t len, const uint16_t *m)
+{
+	uint32_t m_ebitlen, m_rbitlen;
+	size_t mblen, k;
+	const unsigned char *buf;
+	uint32_t acc;
+	int acc_len;
+
+	/*
+	 * Get the encoded bit length.
+	 */
+	m_ebitlen = m[0];
+
+	/*
+	 * Special case for an invalid (null) modulus.
+	 */
+	if (m_ebitlen == 0) {
+		x[0] = 0;
+		return;
+	}
+
+	/*
+	 * Clear the destination.
+	 */
+	br_i15_zero(x, m_ebitlen);
+
+	/*
+	 * First decode directly as many bytes as possible. This requires
+	 * computing the actual bit length.
+	 */
+	m_rbitlen = m_ebitlen >> 4;
+	m_rbitlen = (m_ebitlen & 15) + (m_rbitlen << 4) - m_rbitlen;
+	mblen = (m_rbitlen + 7) >> 3;
+	k = mblen - 1;
+	if (k >= len) {
+		br_i15_decode(x, src, len);
+		x[0] = m_ebitlen;
+		return;
+	}
+	buf = src;
+	br_i15_decode(x, buf, k);
+	x[0] = m_ebitlen;
+
+	/*
+	 * Input remaining bytes, using 15-bit words.
+	 */
+	acc = 0;
+	acc_len = 0;
+	while (k < len) {
+		uint32_t v;
+
+		v = buf[k ++];
+		acc = (acc << 8) | v;
+		acc_len += 8;
+		if (acc_len >= 15) {
+			br_i15_muladd_small(x, acc >> (acc_len - 15), m);
+			acc_len -= 15;
+			acc &= ~((uint32_t)-1 << acc_len);
+		}
+	}
+
+	/*
+	 * We may have some bits accumulated. We then perform a shift to
+	 * be able to inject these bits as a full 15-bit word.
+	 */
+	if (acc_len != 0) {
+		acc = (acc | (x[1] << acc_len)) & 0x7FFF;
+		br_i15_rshift(x, 15 - acc_len);
+		br_i15_muladd_small(x, acc, m);
+	}
+}