1 /* Round toward nearest, breaking ties away from zero.
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 /* Written by Ben Pfaff <blp@gnu.org>, 2007.
19 Based heavily on code by Bruno Haible. */
21 #if ! defined USE_LONG_DOUBLE
32 #ifdef USE_LONG_DOUBLE
36 # define DOUBLE long double
37 # define MANT_DIG LDBL_MANT_DIG
39 # define L_(literal) literal##L
40 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORL_AND_CEILL
41 #elif ! defined USE_FLOAT
45 # define DOUBLE double
46 # define MANT_DIG DBL_MANT_DIG
48 # define L_(literal) literal
49 # define HAVE_FLOOR_AND_CEIL 1
50 #else /* defined USE_FLOAT */
55 # define MANT_DIG FLT_MANT_DIG
57 # define L_(literal) literal##f
58 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORF_AND_CEILF
61 /* -0.0. See minus-zero.h. */
62 #if defined __hpux || defined __sgi || defined __ICC
63 # define MINUS_ZERO (-MIN * MIN)
65 # define MINUS_ZERO L_(-0.0)
68 /* If we're being included from test-round2[f].c, it already defined names for
69 our round implementations. Otherwise, pick the preferred implementation for
71 #if !defined FLOOR_BASED_ROUND && !defined FLOOR_FREE_ROUND
72 # if HAVE_FLOOR_AND_CEIL
73 # define FLOOR_BASED_ROUND ROUND
75 # define FLOOR_FREE_ROUND ROUND
79 #ifdef FLOOR_BASED_ROUND
80 /* An implementation of the C99 round function based on floor and ceil. We use
81 this when floor and ceil are available, on the assumption that they are
82 faster than the open-coded versions below. */
84 FLOOR_BASED_ROUND (DOUBLE x)
101 #endif /* FLOOR_BASED_ROUND */
103 #ifdef FLOOR_FREE_ROUND
104 /* An implementation of the C99 round function without floor or ceil.
105 We use this when floor or ceil is missing. */
107 FLOOR_FREE_ROUND (DOUBLE x)
109 /* 2^(MANT_DIG-1). */
110 static const DOUBLE TWO_MANT_DIG =
111 /* Assume MANT_DIG <= 5 * 31.
113 n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */
114 (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
115 * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
116 * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
117 * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
118 * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
120 /* The use of 'volatile' guarantees that excess precision bits are dropped at
121 each addition step and before the following comparison at the caller's
122 site. It is necessary on x86 systems where double-floats are not IEEE
123 compliant by default, to avoid that the results become platform and
124 compiler option dependent. 'volatile' is a portable alternative to gcc's
125 -ffloat-store option. */
126 volatile DOUBLE y = x;
127 volatile DOUBLE z = y;
131 /* Avoid rounding error for x = 0.5 - 2^(-MANT_DIG-1). */
134 /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */
135 else if (z < TWO_MANT_DIG)
137 /* Add 0.5 to the absolute value. */
139 /* Round to the next integer (nearest or up or down, doesn't
143 /* Enforce rounding down. */
148 else if (z < L_(0.0))
150 /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)). */
153 /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */
154 else if (z > -TWO_MANT_DIG)
156 /* Add 0.5 to the absolute value. */
158 /* Round to the next integer (nearest or up or down, doesn't
162 /* Enforce rounding up. */
169 #endif /* FLOOR_FREE_ROUND */