mirror of https://github.com/ClassiCube/ClassiCube
67 lines
2.0 KiB
C
67 lines
2.0 KiB
C
/*
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* Copyright (c) 2016 Thomas Pornin <pornin@bolet.org>
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*
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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* BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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* ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*/
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#include "inner.h"
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/* see inner.h */
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void
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br_i31_reduce(uint32_t *x, const uint32_t *a, const uint32_t *m)
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{
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uint32_t m_bitlen, a_bitlen;
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size_t mlen, alen, u;
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m_bitlen = m[0];
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mlen = (m_bitlen + 31) >> 5;
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x[0] = m_bitlen;
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if (m_bitlen == 0) {
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return;
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}
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/*
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* If the source is shorter, then simply copy all words from a[]
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* and zero out the upper words.
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*/
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a_bitlen = a[0];
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alen = (a_bitlen + 31) >> 5;
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if (a_bitlen < m_bitlen) {
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br_memcpy(x + 1, a + 1, alen * sizeof *a);
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for (u = alen; u < mlen; u ++) {
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x[u + 1] = 0;
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}
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return;
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}
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/*
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* The source length is at least equal to that of the modulus.
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* We must thus copy N-1 words, and input the remaining words
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* one by one.
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*/
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br_memcpy(x + 1, a + 2 + (alen - mlen), (mlen - 1) * sizeof *a);
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x[mlen] = 0;
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for (u = 1 + alen - mlen; u > 0; u --) {
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br_i31_muladd_small(x, a[u], m);
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}
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}
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