mirror of
https://github.com/cryb-to/cryb-to.git
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66 lines
2 KiB
C
66 lines
2 KiB
C
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/*
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* Copyright (c) 2017 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 <errno.h>
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#include <stddef.h>
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#include <stdint.h>
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#include <strings.h>
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#include <cryb/bitwise.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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* Decrement X in place.
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*/
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int
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mpi_dec_abs(cryb_mpi *X)
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{
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unsigned int i;
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/* trivial case: zero */
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if (X->msb == 0) {
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errno = EINVAL;
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return (-1);
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}
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/* decrement least-significant word and propagate */
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for (i = 0; X->words[i]-- == 0; ++i)
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/* nothing */;
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i = X->msb / 32;
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if (X->words[i] == 0)
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--i;
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X->msb = i * 32 + flsl(X->words[i]);
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return (0);
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}
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