1 /* Handle floating-point rounding mode within libc.
2 Copyright (C) 2012-2022 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4
5 The GNU C Library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 The GNU C Library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with the GNU C Library; if not, see
17 <https://www.gnu.org/licenses/>. */
18
19 #ifndef _ROUNDING_MODE_H
20 #define _ROUNDING_MODE_H 1
21
22 #include <fenv.h>
23 #include <stdbool.h>
24 #include <stdlib.h>
25
26 /* Get the architecture-specific definition of how to determine the
27 rounding mode in libc. This header must also define the FE_*
28 macros for any standard rounding modes the architecture does not
29 have in <fenv.h>, to arbitrary distinct values. */
30 #include <get-rounding-mode.h>
31
32 /* Return true if a number should be rounded away from zero in
33 rounding mode MODE, false otherwise. NEGATIVE is true if the
34 number is negative, false otherwise. LAST_DIGIT_ODD is true if the
35 last digit of the truncated value (last bit for binary) is odd,
36 false otherwise. HALF_BIT is true if the number is at least half
37 way from the truncated value to the next value with the
38 least-significant digit in the same place, false otherwise.
39 MORE_BITS is true if the number is not exactly equal to the
40 truncated value or the half-way value, false otherwise. */
41
42 static bool
round_away(bool negative,bool last_digit_odd,bool half_bit,bool more_bits,int mode)43 round_away (bool negative, bool last_digit_odd, bool half_bit, bool more_bits,
44 int mode)
45 {
46 switch (mode)
47 {
48 case FE_DOWNWARD:
49 return negative && (half_bit || more_bits);
50
51 case FE_TONEAREST:
52 return half_bit && (last_digit_odd || more_bits);
53
54 case FE_TOWARDZERO:
55 return false;
56
57 case FE_UPWARD:
58 return !negative && (half_bit || more_bits);
59
60 default:
61 abort ();
62 }
63 }
64
65 #endif /* rounding-mode.h */
66