1/* Round to nearest integer value, rounding halfway cases to even.
2 dbl-64/wordsize-64 version.
3 Copyright (C) 2016-2019 Free Software Foundation, Inc.
4 This file is part of the GNU C Library.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 The GNU C Library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
15
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, see
18 <http://www.gnu.org/licenses/>. */
19
20#include <math.h>
21#include <math_private.h>
22#include <libm-alias-double.h>
23#include <stdint.h>
24
25#define BIAS 0x3ff
26#define MANT_DIG 53
27#define MAX_EXP (2 * BIAS + 1)
28
29double
30__roundeven (double x)
31{
32 uint64_t ix, ux;
33 EXTRACT_WORDS64 (ix, x);
34 ux = ix & 0x7fffffffffffffffULL;
35 int exponent = ux >> (MANT_DIG - 1);
36 if (exponent >= BIAS + MANT_DIG - 1)
37 {
38 /* Integer, infinity or NaN. */
39 if (exponent == MAX_EXP)
40 /* Infinity or NaN; quiet signaling NaNs. */
41 return x + x;
42 else
43 return x;
44 }
45 else if (exponent >= BIAS)
46 {
47 /* At least 1; not necessarily an integer. Locate the bits with
48 exponents 0 and -1 (when the unbiased exponent is 0, the bit
49 with exponent 0 is implicit, but as the bias is odd it is OK
50 to take it from the low bit of the exponent). */
51 int int_pos = (BIAS + MANT_DIG - 1) - exponent;
52 int half_pos = int_pos - 1;
53 uint64_t half_bit = 1ULL << half_pos;
54 uint64_t int_bit = 1ULL << int_pos;
55 if ((ix & (int_bit | (half_bit - 1))) != 0)
56 /* Carry into the exponent works correctly. No need to test
57 whether HALF_BIT is set. */
58 ix += half_bit;
59 ix &= ~(int_bit - 1);
60 }
61 else if (exponent == BIAS - 1 && ux > 0x3fe0000000000000ULL)
62 /* Interval (0.5, 1). */
63 ix = (ix & 0x8000000000000000ULL) | 0x3ff0000000000000ULL;
64 else
65 /* Rounds to 0. */
66 ix &= 0x8000000000000000ULL;
67 INSERT_WORDS64 (x, ix);
68 return x;
69}
70hidden_def (__roundeven)
71libm_alias_double (__roundeven, roundeven)
72