blob: ded15bc782cb4740ff3e15ec38b79950a549f005 [file] [log] [blame]
/* Copyright (c) 2014, Intel Corporation.
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */
#include "ecp_nistz.h"
/* Fills |str| with the bytewise little-endian encoding of |scalar|, where
* |scalar| has |num_limbs| limbs. |str| is padded with zeros at the end up
* to |str_len| bytes. Actually, |str_len| must be exactly one byte more than
* needed to encode |num_limbs| losslessly, so that there is an extra byte at
* the end. The extra byte is useful because the caller will be breaking |str|
* up into windows of a number of bits (5 or 7) that isn't divisible by 8, and
* so it is useful for it to be able to read an extra zero byte. */
void gfp_little_endian_bytes_from_scalar(uint8_t str[], size_t str_len,
const Limb scalar[],
size_t num_limbs) {
assert(str_len == (num_limbs * sizeof(Limb)) + 1);
size_t i;
for (i = 0; i < num_limbs * sizeof(Limb); i += sizeof(Limb)) {
Limb d = scalar[i / sizeof(Limb)];
str[i + 0] = d & 0xff;
str[i + 1] = (d >> 8) & 0xff;
str[i + 2] = (d >> 16) & 0xff;
str[i + 3] = (d >>= 24) & 0xff;
if (sizeof(Limb) == 8) {
d >>= 8;
str[i + 4] = d & 0xff;
str[i + 5] = (d >> 8) & 0xff;
str[i + 6] = (d >> 16) & 0xff;
str[i + 7] = (d >> 24) & 0xff;
}
}
for (; i < str_len; i++) {
str[i] = 0;
}
}