X-Git-Url: https://bearssl.org/gitweb//home/git/?p=BearSSL;a=blobdiff_plain;f=src%2Fint%2Fi15_reduce.c;fp=src%2Fint%2Fi15_reduce.c;h=0931b10495bbb5f1abc5b5007ad9ffa0106a333c;hp=0000000000000000000000000000000000000000;hb=2f454aad577ae53798935cc32438a2d3f02ba31f;hpb=bd3036844bd20b2b8d7bce7fee5ad010ce401915

diff --git a/src/int/i15_reduce.c b/src/int/i15_reduce.c
new file mode 100644
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--- /dev/null
+++ b/src/int/i15_reduce.c
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+/*
+ * 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_reduce(uint16_t *x, const uint16_t *a, const uint16_t *m)
+{
+	uint32_t m_bitlen, a_bitlen;
+	size_t mlen, alen, u;
+
+	m_bitlen = m[0];
+	mlen = (m_bitlen + 15) >> 4;
+
+	x[0] = m_bitlen;
+	if (m_bitlen == 0) {
+		return;
+	}
+
+	/*
+	 * If the source is shorter, then simply copy all words from a[]
+	 * and zero out the upper words.
+	 */
+	a_bitlen = a[0];
+	alen = (a_bitlen + 15) >> 4;
+	if (a_bitlen < m_bitlen) {
+		memcpy(x + 1, a + 1, alen * sizeof *a);
+		for (u = alen; u < mlen; u ++) {
+			x[u + 1] = 0;
+		}
+		return;
+	}
+
+	/*
+	 * The source length is at least equal to that of the modulus.
+	 * We must thus copy N-1 words, and input the remaining words
+	 * one by one.
+	 */
+	memcpy(x + 1, a + 2 + (alen - mlen), (mlen - 1) * sizeof *a);
+	x[mlen] = 0;
+	for (u = 1 + alen - mlen; u > 0; u --) {
+		br_i15_muladd_small(x, a[u], m);
+	}
+}