108 lines
2.7 KiB
C
108 lines
2.7 KiB
C
/*
|
|
* Copyright (c) 2016 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_i32_decode_reduce(uint32_t *x,
|
|
const void *src, size_t len, const uint32_t *m)
|
|
{
|
|
uint32_t m_bitlen;
|
|
size_t mblen, k, q;
|
|
const unsigned char *buf;
|
|
|
|
m_bitlen = m[0];
|
|
|
|
/*
|
|
* Special case for an invalid modulus.
|
|
*/
|
|
if (m_bitlen == 0) {
|
|
x[0] = 0;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* Clear the destination.
|
|
*/
|
|
br_i32_zero(x, m_bitlen);
|
|
|
|
/*
|
|
* First decode directly as many bytes as possible without
|
|
* reduction, taking care to leave a number of bytes which
|
|
* is a multiple of 4.
|
|
*/
|
|
mblen = (m_bitlen + 7) >> 3;
|
|
k = mblen - 1;
|
|
|
|
/*
|
|
* Up to k bytes can be safely decoded.
|
|
*/
|
|
if (k >= len) {
|
|
br_i32_decode(x, src, len);
|
|
x[0] = m_bitlen;
|
|
return;
|
|
}
|
|
|
|
/*
|
|
* We want to first inject some bytes with direct decoding,
|
|
* then extra bytes by whole 32-bit words. First compute
|
|
* the size that should be injected that way.
|
|
*/
|
|
buf = src;
|
|
q = (len - k + 3) & ~(size_t)3;
|
|
|
|
/*
|
|
* It may happen that this is more than what we already have
|
|
* (by at most 3 bytes). Such a case may happen only with
|
|
* a very short modulus. In that case, we must process the first
|
|
* bytes "manually".
|
|
*/
|
|
if (q > len) {
|
|
int i;
|
|
uint32_t w;
|
|
|
|
w = 0;
|
|
for (i = 0; i < 4; i ++) {
|
|
w <<= 8;
|
|
if (q <= len) {
|
|
w |= buf[len - q];
|
|
}
|
|
q --;
|
|
}
|
|
br_i32_muladd_small(x, w, m);
|
|
} else {
|
|
br_i32_decode(x, buf, len - q);
|
|
x[0] = m_bitlen;
|
|
}
|
|
|
|
/*
|
|
* At that point, we have exactly q bytes to inject, and q is
|
|
* a multiple of 4.
|
|
*/
|
|
for (k = len - q; k < len; k += 4) {
|
|
br_i32_muladd_small(x, br_dec32be(buf + k), m);
|
|
}
|
|
}
|