1 /* Round toward nearest, breaking ties away from zero.
2 Copyright (C) 2007, 2009, 2010 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. */
26 #ifdef USE_LONG_DOUBLE
30 # define DOUBLE long double
31 # define MANT_DIG LDBL_MANT_DIG
32 # define L_(literal) literal##L
33 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORL_AND_CEILL
34 #elif ! defined USE_FLOAT
38 # define DOUBLE double
39 # define MANT_DIG DBL_MANT_DIG
40 # define L_(literal) literal
41 # define HAVE_FLOOR_AND_CEIL 1
42 #else /* defined USE_FLOAT */
47 # define MANT_DIG FLT_MANT_DIG
48 # define L_(literal) literal##f
49 # define HAVE_FLOOR_AND_CEIL HAVE_FLOORF_AND_CEILF
52 /* If we're being included from test-round2[f].c, it already defined names for
53 our round implementations. Otherwise, pick the preferred implementation for
55 #if !defined FLOOR_BASED_ROUND && !defined FLOOR_FREE_ROUND
56 # if HAVE_FLOOR_AND_CEIL
57 # define FLOOR_BASED_ROUND ROUND
59 # define FLOOR_FREE_ROUND ROUND
63 #ifdef FLOOR_BASED_ROUND
64 /* An implementation of the C99 round function based on floor and ceil. We use
65 this when floor and ceil are available, on the assumption that they are
66 faster than the open-coded versions below. */
68 FLOOR_BASED_ROUND (DOUBLE x)
85 #endif /* FLOOR_BASED_ROUND */
87 #ifdef FLOOR_FREE_ROUND
88 /* An implementation of the C99 round function without floor or ceil.
89 We use this when floor or ceil is missing. */
91 FLOOR_FREE_ROUND (DOUBLE x)
94 static const DOUBLE TWO_MANT_DIG =
95 /* Assume MANT_DIG <= 5 * 31.
97 n = floor(n/5) + floor((n+1)/5) + ... + floor((n+4)/5). */
98 (DOUBLE) (1U << ((MANT_DIG - 1) / 5))
99 * (DOUBLE) (1U << ((MANT_DIG - 1 + 1) / 5))
100 * (DOUBLE) (1U << ((MANT_DIG - 1 + 2) / 5))
101 * (DOUBLE) (1U << ((MANT_DIG - 1 + 3) / 5))
102 * (DOUBLE) (1U << ((MANT_DIG - 1 + 4) / 5));
104 /* The use of 'volatile' guarantees that excess precision bits are dropped at
105 each addition step and before the following comparison at the caller's
106 site. It is necessary on x86 systems where double-floats are not IEEE
107 compliant by default, to avoid that the results become platform and
108 compiler option dependent. 'volatile' is a portable alternative to gcc's
109 -ffloat-store option. */
110 volatile DOUBLE y = x;
111 volatile DOUBLE z = y;
115 /* Avoid rounding error for x = 0.5 - 2^(-MANT_DIG-1). */
118 /* Avoid rounding errors for values near 2^k, where k >= MANT_DIG-1. */
119 else if (z < TWO_MANT_DIG)
121 /* Add 0.5 to the absolute value. */
123 /* Round to the next integer (nearest or up or down, doesn't
127 /* Enforce rounding down. */
132 else if (z < L_(0.0))
134 /* Avoid rounding error for x = -(0.5 - 2^(-MANT_DIG-1)). */
137 /* Avoid rounding errors for values near -2^k, where k >= MANT_DIG-1. */
138 else if (z > -TWO_MANT_DIG)
140 /* Add 0.5 to the absolute value. */
142 /* Round to the next integer (nearest or up or down, doesn't
146 /* Enforce rounding up. */
153 #endif /* FLOOR_FREE_ROUND */