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/*
* 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_i31_mulacc(uint32_t *d, const uint32_t *a, const uint32_t *b)
{
size_t alen, blen, u;
uint32_t dl, dh;
alen = (a[0] + 31) >> 5;
blen = (b[0] + 31) >> 5;
/*
* We want to add the two bit lengths, but these are encoded,
* which requires some extra care.
*/
dl = (a[0] & 31) + (b[0] & 31);
dh = (a[0] >> 5) + (b[0] >> 5);
d[0] = (dh << 5) + dl + (~(uint32_t)(dl - 31) >> 31);
for (u = 0; u < blen; u ++) {
uint32_t f;
size_t v;
/*
* Carry always fits on 31 bits; we want to keep it in a
* 32-bit register on 32-bit architectures (on a 64-bit
* architecture, cast down from 64 to 32 bits means
* clearing the high bits, which is not free; on a 32-bit
* architecture, the same operation really means ignoring
* the top register, which has negative or zero cost).
*/
#if BR_64
uint64_t cc;
#else
uint32_t cc;
#endif
f = b[1 + u];
cc = 0;
for (v = 0; v < alen; v ++) {
uint64_t z;
z = (uint64_t)d[1 + u + v] + MUL31(f, a[1 + v]) + cc;
cc = z >> 31;
d[1 + u + v] = (uint32_t)z & 0x7FFFFFFF;
}
d[1 + u + alen] = (uint32_t)cc;
}
}
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