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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 "fmpz.h"
#include "ulong_extras.h"
slong
fmpz_clog(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_clog_ui(n, *b);
if (fmpz_cmp(n, b) <= 0)
return 1;
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--;
}
r += (sign != 0);
}
/* Adjust up */
else if (sign < 0)
{
while (sign < 0)
{
fmpz_mul(t, t, b);
sign = fmpz_cmp(t, n);
r++;
}
}
fmpz_clear(t);
return r;
}
slong
fmpz_clog_ui(const fmpz_t n, ulong b)
{
fmpz_t t;
int sign;
slong r;
if (fmpz_is_one(n))
return 0;
if (b == 2)
{
fmpz_init(t);
fmpz_sub_ui(t, n, 1);
r = fmpz_bits(t);
fmpz_clear(t);
return r;
}
if (!COEFF_IS_MPZ(*n))
return n_clog(*n, b);
if (fmpz_cmp_ui(n, b) <= 0)
return 1;
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--;
}
r += (sign != 0);
}
/* Adjust up */
else if (sign < 0)
{
while (sign < 0)
{
fmpz_mul_ui(t, t, b);
sign = fmpz_cmp(t, n);
r++;
}
}
fmpz_clear(t);
return r;
}