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/*
Copyright (C) 2011 Sebastian Pancratz
Copyright (C) 2011 Fredrik Johansson
This file is part of FLINT.
FLINT is free software: you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License (LGPL) as published
by the Free Software Foundation; either version 3 of the License, or
(at your option) any later version. See <https://www.gnu.org/licenses/>.
*/
#include <math.h>
#include "ulong_extras.h"
#include "fmpz.h"
slong
fmpz_flog(const fmpz_t n, const fmpz_t b)
{
fmpz_t t;
int sign;
slong r;
if (fmpz_is_one(n))
return 0;
if (!COEFF_IS_MPZ(*b))
return fmpz_flog_ui(n, *b);
sign = fmpz_cmp(n, b);
if (sign <= 0)
return (sign == 0) ? 1 : 0;
r = fmpz_dlog(n) / fmpz_dlog(b);
fmpz_init(t);
fmpz_pow_ui(t, b, r);
sign = fmpz_cmp(t, n);
/* Adjust down */
if (sign > 0)
{
while (sign > 0)
{
fmpz_divexact(t, t, b);
sign = fmpz_cmp(t, n);
r--;
}
}
/* Adjust up */
else if (sign < 0)
{
while (1)
{
fmpz_mul(t, t, b);
if (fmpz_cmp(t, n) <= 0)
r++;
else
break;
}
}
fmpz_clear(t);
return r;
}
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;
}