1 /* Round according to the current rounding mode.
2 Copyright (C) 2007, 2010-2011 Free Software Foundation, Inc.
4 This program is free software; you can redistribute it and/or modify
5 it under the terms of the GNU General Public License as published by
6 the Free Software Foundation; either version 2, or (at your option)
9 This program is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 GNU General Public License for more details.
14 You should have received a copy of the GNU General Public License along
15 with this program; if not, write to the Free Software Foundation,
16 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18 #if ! defined USE_LONG_DOUBLE
30 #ifdef USE_LONG_DOUBLE
32 # define DOUBLE long double
33 # define MANT_DIG LDBL_MANT_DIG
35 # define L_(literal) literal##L
36 #elif ! defined USE_FLOAT
38 # define DOUBLE double
39 # define MANT_DIG DBL_MANT_DIG
41 # define L_(literal) literal
42 #else /* defined USE_FLOAT */
45 # define MANT_DIG FLT_MANT_DIG
47 # define L_(literal) literal##f
50 /* -0.0. See minus-zero.h. */
51 #if defined __hpux || defined __sgi || defined __ICC
52 # define MINUS_ZERO (-MIN * MIN)
54 # define MINUS_ZERO L_(-0.0)
61 static const DOUBLE TWO_MANT_DIG =
62 /* Assume MANT_DIG <= 5 * 31.
64 n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */
65 (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
66 * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
67 * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
68 * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
69 * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
71 /* The use of 'volatile' guarantees that excess precision bits are dropped at
72 each addition step and before the following comparison at the caller's
73 site. It is necessary on x86 systems where double-floats are not IEEE
74 compliant by default, to avoid that the results become platform and
75 compiler option dependent. 'volatile' is a portable alternative to gcc's
76 -ffloat-store option. */
77 volatile DOUBLE z = x;
79 /* Consider the current rounding mode, cf.
80 <http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/float.h.html>.
81 This implementation supports only rounds-to-nearest. */
87 /* Avoid rounding error for x = 0.5 - 2^(-MANT_DIG-1). */
90 /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */
91 else if (z < TWO_MANT_DIG)
93 /* Round to the next integer. */
100 /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)). */
103 /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */
104 else if (z > -TWO_MANT_DIG)
106 /* Round to the next integer. */