1 /* mpfr_exp -- exponential of a floating-point number
3 Copyright 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
4 Contributed by the Arenaire and Cacao projects, INRIA.
6 This file is part of the GNU MPFR Library.
8 The GNU MPFR Library is free software; you can redistribute it and/or modify
9 it under the terms of the GNU Lesser General Public License as published by
10 the Free Software Foundation; either version 3 of the License, or (at your
11 option) any later version.
13 The GNU MPFR Library is distributed in the hope that it will be useful, but
14 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
15 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
16 License for more details.
18 You should have received a copy of the GNU Lesser General Public License
19 along with the GNU MPFR Library; see the file COPYING.LESSER. If not, see
20 http://www.gnu.org/licenses/ or write to the Free Software Foundation, Inc.,
21 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA. */
23 #include "mpfr-impl.h"
28 mpfr_exp (mpfr_ptr y, mpfr_srcptr x, mpfr_rnd_t rnd_mode)
33 MPFR_SAVE_EXPO_DECL (expo);
35 MPFR_LOG_FUNC (("x[%#R]=%R rnd=%d", x, x, rnd_mode),
36 ("y[%#R]=%R inexact=%d", y, y, inexact));
38 if (MPFR_UNLIKELY( MPFR_IS_SINGULAR(x) ))
45 else if (MPFR_IS_INF(x))
56 MPFR_ASSERTD(MPFR_IS_ZERO(x));
57 return mpfr_set_ui (y, 1, rnd_mode);
61 /* First, let's detect most overflow and underflow cases. */
65 /* We must extended the exponent range and save the flags now. */
66 MPFR_SAVE_EXPO_MARK (expo);
68 mpfr_init2 (e, sizeof (mpfr_exp_t) * CHAR_BIT);
69 mpfr_init2 (bound, 32);
71 inexact = mpfr_set_exp_t (e, expo.saved_emax, MPFR_RNDN);
72 MPFR_ASSERTD (inexact == 0);
73 mpfr_const_log2 (bound, expo.saved_emax < 0 ? MPFR_RNDD : MPFR_RNDU);
74 mpfr_mul (bound, bound, e, MPFR_RNDU);
75 if (MPFR_UNLIKELY (mpfr_cmp (x, bound) >= 0))
77 /* x > log(2^emax), thus exp(x) > 2^emax */
78 mpfr_clears (e, bound, (mpfr_ptr) 0);
79 MPFR_SAVE_EXPO_FREE (expo);
80 return mpfr_overflow (y, rnd_mode, 1);
83 inexact = mpfr_set_exp_t (e, expo.saved_emin, MPFR_RNDN);
84 MPFR_ASSERTD (inexact == 0);
85 inexact = mpfr_sub_ui (e, e, 2, MPFR_RNDN);
86 MPFR_ASSERTD (inexact == 0);
87 mpfr_const_log2 (bound, expo.saved_emin < 0 ? MPFR_RNDU : MPFR_RNDD);
88 mpfr_mul (bound, bound, e, MPFR_RNDD);
89 if (MPFR_UNLIKELY (mpfr_cmp (x, bound) <= 0))
91 /* x < log(2^(emin - 2)), thus exp(x) < 2^(emin - 2) */
92 mpfr_clears (e, bound, (mpfr_ptr) 0);
93 MPFR_SAVE_EXPO_FREE (expo);
94 return mpfr_underflow (y, rnd_mode == MPFR_RNDN ? MPFR_RNDZ : rnd_mode,
98 /* Other overflow/underflow cases must be detected
99 by the generic routines. */
100 mpfr_clears (e, bound, (mpfr_ptr) 0);
101 MPFR_SAVE_EXPO_FREE (expo);
104 expx = MPFR_GET_EXP (x);
105 precy = MPFR_PREC (y);
107 /* if x < 2^(-precy), then exp(x) i.e. gives 1 +/- 1 ulp(1) */
108 if (MPFR_UNLIKELY (expx < 0 && (mpfr_uexp_t) (-expx) > precy))
110 mpfr_exp_t emin = __gmpfr_emin;
111 mpfr_exp_t emax = __gmpfr_emax;
112 int signx = MPFR_SIGN (x);
115 if (MPFR_IS_NEG_SIGN (signx) && (rnd_mode == MPFR_RNDD ||
116 rnd_mode == MPFR_RNDZ))
120 mpfr_setmax (y, 0); /* y = 1 - epsilon */
127 mpfr_setmin (y, 1); /* y = 1 */
128 if (MPFR_IS_POS_SIGN (signx) && (rnd_mode == MPFR_RNDU ||
129 rnd_mode == MPFR_RNDA))
134 yn = 1 + (MPFR_PREC(y) - 1) / GMP_NUMB_BITS;
135 sh = (mpfr_prec_t) yn * GMP_NUMB_BITS - MPFR_PREC(y);
136 MPFR_MANT(y)[0] += MPFR_LIMB_ONE << sh;
140 inexact = -MPFR_FROM_SIGN_TO_INT(signx);
146 else /* General case */
148 if (MPFR_UNLIKELY (precy >= MPFR_EXP_THRESHOLD))
149 /* mpfr_exp_3 saves the exponent range and flags itself, otherwise
150 the flag changes in mpfr_exp_3 are lost */
151 inexact = mpfr_exp_3 (y, x, rnd_mode); /* O(M(n) log(n)^2) */
154 MPFR_SAVE_EXPO_MARK (expo);
155 inexact = mpfr_exp_2 (y, x, rnd_mode); /* O(n^(1/3) M(n)) */
156 MPFR_SAVE_EXPO_UPDATE_FLAGS (expo, __gmpfr_flags);
157 MPFR_SAVE_EXPO_FREE (expo);
161 return mpfr_check_range (y, inexact, rnd_mode);