mirror of
https://github.com/vale981/arb
synced 2025-03-05 09:21:38 -05:00
96 lines
2.7 KiB
C
96 lines
2.7 KiB
C
/*=============================================================================
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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
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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ARB is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with ARB; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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=============================================================================*/
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/******************************************************************************
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Copyright (C) 2014 Fredrik Johansson
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******************************************************************************/
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#include "flint/double_extras.h"
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#include "mag.h"
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void
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mag_log1p(mag_t z, const mag_t x)
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{
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if (mag_is_special(x))
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{
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if (mag_is_zero(x))
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mag_zero(z);
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else
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mag_inf(z);
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}
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else
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{
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fmpz exp = MAG_EXP(x);
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if (!COEFF_IS_MPZ(exp))
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{
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/* Quick bound by x */
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if (exp < -10)
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{
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mag_set(z, x);
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return;
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}
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else if (exp < 1000)
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{
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double t;
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t = ldexp(MAG_MAN(x), exp - MAG_BITS);
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t = (1.0 + t) * (1 + 1e-14);
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t = mag_d_log_upper_bound(t);
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mag_set_d(z, t);
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return;
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}
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}
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else if (fmpz_sgn(MAG_EXPREF(x)) < 0)
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{
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/* Quick bound by x */
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mag_set(z, x);
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return;
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}
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/* Now we must have x >= 2^1000 */
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/* Use log(2^(exp-1) * (2*v)) = exp*log(2) + log(2*v) */
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{
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double t;
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fmpz_t b;
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mag_t u;
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mag_init(u);
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fmpz_init(b);
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/* incrementing the mantissa gives an upper bound for x+1 */
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t = ldexp(MAG_MAN(x) + 1, 1 - MAG_BITS);
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t = mag_d_log_upper_bound(t);
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mag_set_d(u, t);
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/* log(2) < 744261118/2^30 */
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_fmpz_add_fast(b, MAG_EXPREF(x), -1);
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fmpz_mul_ui(b, b, 744261118);
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mag_set_fmpz(z, b);
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_fmpz_add_fast(MAG_EXPREF(z), MAG_EXPREF(z), -30);
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mag_add(z, z, u);
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mag_clear(u);
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fmpz_clear(b);
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}
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}
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}
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