59 lines
1.9 KiB
C
59 lines
1.9 KiB
C
/*
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* Copyright (c) 2017 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_i15_from_monty(uint16_t *x, const uint16_t *m, uint16_t m0i)
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{
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size_t len, u, v;
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len = (m[0] + 15) >> 4;
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for (u = 0; u < len; u ++) {
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uint32_t f, cc;
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f = MUL15(x[1], m0i) & 0x7FFF;
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cc = 0;
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for (v = 0; v < len; v ++) {
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uint32_t z;
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z = (uint32_t)x[v + 1] + MUL15(f, m[v + 1]) + cc;
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cc = z >> 15;
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if (v != 0) {
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x[v] = z & 0x7FFF;
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}
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}
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x[len] = cc;
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}
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/*
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* We may have to do an extra subtraction, but only if the
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* value in x[] is indeed greater than or equal to that of m[],
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* which is why we must do two calls (first call computes the
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* carry, second call performs the subtraction only if the carry
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* is 0).
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*/
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br_i15_sub(x, m, NOT(br_i15_sub(x, m, 0)));
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}
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