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43 lines
980 B
C
43 lines
980 B
C
/*
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Copyright (C) 2014 Fredrik Johansson
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This file is part of Arb.
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Arb is free software: you can redistribute it and/or modify it under
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the terms of the GNU Lesser General Public License (LGPL) as published
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by the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version. See <http://www.gnu.org/licenses/>.
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*/
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#include "mag.h"
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double
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mag_get_d_log2_approx(const mag_t x)
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{
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if (mag_is_zero(x))
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{
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return COEFF_MIN;
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}
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else if (mag_is_inf(x))
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{
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return COEFF_MAX;
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}
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else if (COEFF_IS_MPZ(MAG_EXP(x)))
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{
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if (fmpz_sgn(MAG_EXPREF(x)) < 0)
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return COEFF_MIN;
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else
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return COEFF_MAX;
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}
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else
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{
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slong e = MAG_EXP(x);
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if (e < -20 || e > 20)
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return e;
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else
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return e + 1.4426950408889634074 *
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mag_d_log_upper_bound(MAG_MAN(x) * ldexp(1.0, -MAG_BITS));
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}
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}
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