1/* Round to nearest integer value, rounding halfway cases to even.
2 Copyright (C) 2016-2023 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#define NO_MATH_REDIRECT
20#include <math.h>
21#include <math_private.h>
22#include <libm-alias-double.h>
23#include <stdint.h>
24#include <math-use-builtins.h>
25
26#define BIAS 0x3ff
27#define MANT_DIG 53
28#define MAX_EXP (2 * BIAS + 1)
29
30double
31__roundeven (double x)
32{
33#if USE_ROUNDEVEN_BUILTIN
34 return __builtin_roundeven (x);
35#else
36 uint64_t ix, ux;
37 EXTRACT_WORDS64 (ix, x);
38 ux = ix & 0x7fffffffffffffffULL;
39 int exponent = ux >> (MANT_DIG - 1);
40 if (exponent >= BIAS + MANT_DIG - 1)
41 {
42 /* Integer, infinity or NaN. */
43 if (exponent == MAX_EXP)
44 /* Infinity or NaN; quiet signaling NaNs. */
45 return x + x;
46 else
47 return x;
48 }
49 else if (exponent >= BIAS)
50 {
51 /* At least 1; not necessarily an integer. Locate the bits with
52 exponents 0 and -1 (when the unbiased exponent is 0, the bit
53 with exponent 0 is implicit, but as the bias is odd it is OK
54 to take it from the low bit of the exponent). */
55 int int_pos = (BIAS + MANT_DIG - 1) - exponent;
56 int half_pos = int_pos - 1;
57 uint64_t half_bit = 1ULL << half_pos;
58 uint64_t int_bit = 1ULL << int_pos;
59 if ((ix & (int_bit | (half_bit - 1))) != 0)
60 /* Carry into the exponent works correctly. No need to test
61 whether HALF_BIT is set. */
62 ix += half_bit;
63 ix &= ~(int_bit - 1);
64 }
65 else if (exponent == BIAS - 1 && ux > 0x3fe0000000000000ULL)
66 /* Interval (0.5, 1). */
67 ix = (ix & 0x8000000000000000ULL) | 0x3ff0000000000000ULL;
68 else
69 /* Rounds to 0. */
70 ix &= 0x8000000000000000ULL;
71 INSERT_WORDS64 (x, ix);
72 return x;
73#endif /* ! USE_ROUNDEVEN_BUILTIN */
74}
75#ifndef __roundeven
76libm_alias_double (__roundeven, roundeven)
77#endif
78