pqc/external/flint-2.4.3/ulong_extras/revbin.c

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2014-05-18 22:03:37 +00:00
/*=============================================================================
This file is part of FLINT.
FLINT is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
FLINT is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with FLINT; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
=============================================================================*/
/******************************************************************************
Copyright (C) 2009 William Hart
******************************************************************************/
#include <gmp.h>
#include "flint.h"
#include "ulong_extras.h"
const ulong flint_revtab0[1] = { 0 };
const ulong flint_revtab1[2] = { 0, 1 };
const ulong flint_revtab2[4] = { 0, 2, 1, 3 };
const ulong flint_revtab3[8] = { 0, 4, 2, 6, 1, 5, 3, 7 };
const ulong flint_revtab4[16] = { 0, 8, 4, 12, 2, 10, 6, 14, 1, 9, 5, 13, 3, 11, 7, 15 };
const ulong * flint_revtab[5] = { flint_revtab0, flint_revtab1, flint_revtab2, flint_revtab3, flint_revtab4 };
/*
computes the reverse binary of a binary number of the given number of bits
*/
ulong n_revbin(ulong in, ulong bits)
{
ulong out = 0, i;
if (bits <= 4)
return flint_revtab[bits][in];
for (i = 0; i < bits; i++)
{
out <<= 1;
out += (in & 1);
in >>= 1;
}
return out;
}