pqc/external/flint-2.4.3/fmpz/flog_ui.c

86 lines
2.1 KiB
C

/*=============================================================================
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) 2011 Sebastian Pancratz
Copyright (C) 2011 Fredrik Johansson
******************************************************************************/
#include <math.h>
#include <gmp.h>
#include "flint.h"
#include "fmpz.h"
#include "ulong_extras.h"
slong
fmpz_flog_ui(const fmpz_t n, ulong b)
{
fmpz_t t;
int sign;
slong r;
if (fmpz_is_one(n))
return 0;
if (b == 2)
return fmpz_bits(n) - 1;
if (!COEFF_IS_MPZ(*n))
return n_flog(*n, b);
sign = fmpz_cmp_ui(n, b);
if (sign <= 0)
return (sign == 0) ? 1 : 0;
r = fmpz_dlog(n) / log(b);
fmpz_init(t);
fmpz_set_ui(t, b);
fmpz_pow_ui(t, t, r);
sign = fmpz_cmp(t, n);
/* Adjust down */
if (sign > 0)
{
while (sign > 0)
{
fmpz_divexact_ui(t, t, b);
sign = fmpz_cmp(t, n);
r--;
}
}
/* Adjust up */
else if (sign < 0)
{
while (1)
{
fmpz_mul_ui(t, t, b);
if (fmpz_cmp(t, n) <= 0)
r++;
else
break;
}
}
fmpz_clear(t);
return r;
}