X-Git-Url: https://www.bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fint%2Fi15_montmul.c;fp=src%2Fint%2Fi15_montmul.c;h=8da938fb7704594dba9d9cb47920d7d68dcb4fc4;hp=0000000000000000000000000000000000000000;hb=2f454aad577ae53798935cc32438a2d3f02ba31f;hpb=bd3036844bd20b2b8d7bce7fee5ad010ce401915

diff --git a/src/int/i15_montmul.c b/src/int/i15_montmul.c
new file mode 100644
index 0000000..8da938f
--- /dev/null
+++ b/src/int/i15_montmul.c
@@ -0,0 +1,91 @@
+/*
+ * 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_montymul(uint16_t *d, const uint16_t *x, const uint16_t *y,
+	const uint16_t *m, uint16_t m0i)
+{
+	size_t len, len4, u, v;
+	uint32_t dh;
+
+	len = (m[0] + 15) >> 4;
+	len4 = len & ~(size_t)3;
+	br_i15_zero(d, m[0]);
+	dh = 0;
+	for (u = 0; u < len; u ++) {
+		uint32_t f, xu, r, zh;
+
+		xu = x[u + 1];
+		f = MUL15((d[1] + MUL15(x[u + 1], y[1])) & 0x7FFF, m0i)
+			& 0x7FFF;
+
+		r = 0;
+		for (v = 0; v < len4; v += 4) {
+			uint32_t z;
+
+			z = d[v + 1] + MUL15(xu, y[v + 1])
+				+ MUL15(f, m[v + 1]) + r;
+			r = z >> 15;
+			d[v + 0] = z & 0x7FFF;
+			z = d[v + 2] + MUL15(xu, y[v + 2])
+				+ MUL15(f, m[v + 2]) + r;
+			r = z >> 15;
+			d[v + 1] = z & 0x7FFF;
+			z = d[v + 3] + MUL15(xu, y[v + 3])
+				+ MUL15(f, m[v + 3]) + r;
+			r = z >> 15;
+			d[v + 2] = z & 0x7FFF;
+			z = d[v + 4] + MUL15(xu, y[v + 4])
+				+ MUL15(f, m[v + 4]) + r;
+			r = z >> 15;
+			d[v + 3] = z & 0x7FFF;
+		}
+		for (; v < len; v ++) {
+			uint32_t z;
+
+			z = d[v + 1] + MUL15(xu, y[v + 1])
+				+ MUL15(f, m[v + 1]) + r;
+			r = z >> 15;
+			d[v + 0] = z & 0x7FFF;
+		}
+
+		zh = dh + r;
+		d[len] = zh & 0x7FFF;
+		dh = zh >> 15;
+	}
+
+	/*
+	 * Restore the bit length (it was overwritten in the loop above).
+	 */
+	d[0] = m[0];
+
+	/*
+	 * d[] may be greater than m[], but it is still lower than twice
+	 * the modulus.
+	 */
+	br_i15_sub(d, m, NEQ(dh, 0) | NOT(br_i15_sub(d, m, 0)));
+}