mirror of
https://github.com/vale981/arb
synced 2025-03-06 01:41:39 -05:00
122 lines
3.1 KiB
C
122 lines
3.1 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 "arf.h"
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#include "double_extras.h"
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/* most double: (2^53-1) * 2^971 */
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/* least normal: 2^-1022 */
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/* least subnormal: 2^-1074 */
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static double
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huge_double(arf_rnd_t rnd, int negative)
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{
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double v;
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if (rnd == ARF_RND_NEAR || rounds_up(rnd, negative))
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v = D_INF;
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else
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v = ldexp(9007199254740991.0, 971);
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return negative ? -v : v;
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}
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static double
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tiny_double(arf_rnd_t rnd, int negative)
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{
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double v;
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if (rnd == ARF_RND_NEAR || !rounds_up(rnd, negative))
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v = 0.0;
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else
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v = ldexp(1.0, -1074);
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return negative ? -v : v;
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}
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double
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arf_get_d(const arf_t x, arf_rnd_t rnd)
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{
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if (arf_is_special(x))
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{
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if (arf_is_zero(x))
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return 0.0;
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else if (arf_is_pos_inf(x))
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return D_INF;
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else if (arf_is_neg_inf(x))
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return -D_INF;
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else
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return D_NAN;
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}
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else
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{
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arf_t t;
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mp_srcptr tp;
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mp_size_t tn;
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double v;
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/* also catches bignum exponents */
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if (ARF_EXP(x) > 1030 || ARF_EXP(x) < -1080)
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{
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if (fmpz_sgn(ARF_EXPREF(x)) > 0)
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return huge_double(rnd, ARF_SGNBIT(x));
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else
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return tiny_double(rnd, ARF_SGNBIT(x));
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}
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/* allow mpfr to take care of corner cases for now */
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if (ARF_EXP(x) > 1020 || ARF_EXP(x) <= -1020 || rnd == ARF_RND_NEAR)
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{
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mpfr_t xx;
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ARF_GET_MPN_READONLY(tp, tn, x);
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xx->_mpfr_d = (mp_ptr) tp;
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xx->_mpfr_prec = tn * FLINT_BITS;
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xx->_mpfr_sign = ARF_SGNBIT(x) ? -1 : 1;
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xx->_mpfr_exp = ARF_EXP(x);
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return mpfr_get_d(xx, rnd_to_mpfr(rnd));
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}
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arf_init(t);
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arf_set_round(t, x, 53, rnd);
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ARF_GET_MPN_READONLY(tp, tn, t);
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if (tn == 1)
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v = (double)(tp[0]);
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else
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v = (double)(tp[1]) + (double)(tp[0]) * ldexp(1,-32);
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v = ldexp(v, ARF_EXP(t) - FLINT_BITS);
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if (ARF_SGNBIT(t))
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v = -v;
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arf_clear(t);
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return v;
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}
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}
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