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/*
Copyright (C) 2014 Fredrik Johansson
This file is part of Arb.
Arb 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 2.1 of the License, or
(at your option) any later version. See <http://www.gnu.org/licenses/>.
*/
#include "mag.h"
double
mag_get_d_log2_approx(const mag_t x)
{
if (mag_is_zero(x))
{
return COEFF_MIN;
}
else if (mag_is_inf(x))
{
return COEFF_MAX;
}
else if (COEFF_IS_MPZ(MAG_EXP(x)))
{
if (fmpz_sgn(MAG_EXPREF(x)) < 0)
return COEFF_MIN;
else
return COEFF_MAX;
}
else
{
slong e = MAG_EXP(x);
if (e < -20 || e > 20)
return e;
else
return e + 1.4426950408889634074 *
mag_d_log_upper_bound(MAG_MAN(x) * ldexp(1.0, -MAG_BITS));
}
}
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