+/*
+ * 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)));
+}