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https://github.com/cryb-to/cryb-to.git
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76 lines
2.4 KiB
C
76 lines
2.4 KiB
C
/*
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* Copyright (c) 2014-2016 Dag-Erling Smørgrav
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
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* products derived from this software without specific prior written
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* permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include "cryb/impl.h"
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#include <stdint.h>
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#include <string.h>
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#include <cryb/mpi.h>
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#include "cryb_mpi_impl.h"
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/*
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* Right-shift X by c bytes
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*/
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int
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mpi_rshift(cryb_mpi *X, unsigned int c)
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{
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unsigned int cl, i;
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/* operands are zero */
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if (c == 0 || X->msb == 0)
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return (0);
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/* shift wider than number, result is zero */
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if (X->msb <= c) {
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mpi_zero(X);
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return (0);
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}
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/* preemptively adjust msb */
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X->msb -= c;
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/* try to move whole words first */
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if (c >= 32) {
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cl = c / 32;
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c = c % 32;
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memmove(X->words, X->words + cl,
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(X->size - cl) * sizeof *X->words);
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memset(X->words + X->size - cl, 0, cl * sizeof *X->words);
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}
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/* done? */
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if (c == 0)
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return (0);
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/* the rest has to be done the hard way */
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for (i = 0; i < X->size - 1; ++i) {
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X->words[i] >>= c;
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X->words[i] |= X->words[i + 1] << (32 - c);
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}
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X->words[X->size - 1] >>= c;
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/* done! */
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return (0);
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}
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