--- /dev/null
+/*
+ * 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"
+
+/*
+ * This file contains some additional functions for "i15" big integers.
+ * These functions are needed to support ECDSA.
+ */
+
+/* see inner.h */
+void
+br_i15_rshift(uint16_t *x, int count)
+{
+ size_t u, len;
+ unsigned r;
+
+ len = (x[0] + 15) >> 4;
+ if (len == 0) {
+ return;
+ }
+ r = x[1] >> count;
+ for (u = 2; u <= len; u ++) {
+ unsigned w;
+
+ w = x[u];
+ x[u - 1] = ((w << (15 - count)) | r) & 0x7FFF;
+ r = w >> count;
+ }
+ x[len] = r;
+}
+
+/* see inner.h */
+uint32_t
+br_i15_bit_length(uint16_t *x, size_t xlen)
+{
+ uint32_t tw, twk;
+
+ tw = 0;
+ twk = 0;
+ while (xlen -- > 0) {
+ uint32_t w, c;
+
+ c = EQ(tw, 0);
+ w = x[xlen];
+ tw = MUX(c, w, tw);
+ twk = MUX(c, (uint32_t)xlen, twk);
+ }
+ return (twk << 4) + BIT_LENGTH(tw);
+}
+
+/* see inner.h */
+void
+br_i15_decode(uint16_t *x, const void *src, size_t len)
+{
+ const unsigned char *buf;
+ size_t v;
+ uint32_t acc;
+ int acc_len;
+
+ buf = src;
+ v = 1;
+ acc = 0;
+ acc_len = 0;
+ while (len -- > 0) {
+ uint32_t b;
+
+ b = buf[len];
+ acc |= (b << acc_len);
+ acc_len += 8;
+ if (acc_len >= 15) {
+ x[v ++] = acc & 0x7FFF;
+ acc_len -= 15;
+ acc >>= 15;
+ }
+ }
+ if (acc_len != 0) {
+ x[v ++] = acc;
+ }
+ x[0] = br_i15_bit_length(x + 1, v - 1);
+}
+
+/* see inner.h */
+void
+br_i15_from_monty(uint16_t *x, const uint16_t *m, uint16_t m0i)
+{
+ size_t len, u, v;
+
+ len = (m[0] + 15) >> 4;
+ for (u = 0; u < len; u ++) {
+ uint32_t f, cc;
+
+ f = MUL15(x[1], m0i) & 0x7FFF;
+ cc = 0;
+ for (v = 0; v < len; v ++) {
+ uint32_t z;
+
+ z = (uint32_t)x[v + 1] + MUL15(f, m[v + 1]) + cc;
+ cc = z >> 15;
+ if (v != 0) {
+ x[v] = z & 0x7FFF;
+ }
+ }
+ x[len] = cc;
+ }
+
+ /*
+ * We may have to do an extra subtraction, but only if the
+ * value in x[] is indeed greater than or equal to that of m[],
+ * which is why we must do two calls (first call computes the
+ * carry, second call performs the subtraction only if the carry
+ * is 0).
+ */
+ br_i15_sub(x, m, NOT(br_i15_sub(x, m, 0)));
+}