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/*
* Copyright (c) 2016 Thomas Pornin <[email protected]>
*
* 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 */
uint32_t
br_i32_decode_mod(uint32_t *x, const void *src, size_t len, const uint32_t *m)
{
const unsigned char *buf;
uint32_t r;
size_t u, v, mlen;
buf = src;
/*
* First pass: determine whether the value fits. The 'r' value
* will contain the comparison result, as 0x00000000 (value is
* equal to the modulus), 0x00000001 (value is greater than the
* modulus), or 0xFFFFFFFF (value is lower than the modulus).
*/
mlen = (m[0] + 7) >> 3;
r = 0;
for (u = (mlen > len) ? mlen : len; u > 0; u --) {
uint32_t mb, xb;
v = u - 1;
if (v >= mlen) {
mb = 0;
} else {
mb = (m[1 + (v >> 2)] >> ((v & 3) << 3)) & 0xFF;
}
if (v >= len) {
xb = 0;
} else {
xb = buf[len - u];
}
r = MUX(EQ(r, 0), (uint32_t)CMP(xb, mb), r);
}
/*
* Only r == 0xFFFFFFFF is acceptable. We want to set r to 0xFF if
* the value fits, 0x00 otherwise.
*/
r >>= 24;
br_i32_zero(x, m[0]);
u = (mlen > len) ? len : mlen;
while (u > 0) {
uint32_t xb;
xb = buf[len - u] & r;
u --;
x[1 + (u >> 2)] |= xb << ((u & 3) << 3);
}
return r >> 7;
}
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