1/* Round to nearest integer value, rounding halfway cases to even.
2 ldbl-128 version.
3 Copyright (C) 2016-2021 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 <https://www.gnu.org/licenses/>. */
19
20#include <math.h>
21#include <math_private.h>
22#include <libm-alias-ldouble.h>
23#include <stdint.h>
24
25#define BIAS 0x3fff
26#define MANT_DIG 113
27#define MAX_EXP (2 * BIAS + 1)
28
29_Float128
30__roundevenl (_Float128 x)
31{
32 uint64_t hx, lx, uhx;
33 GET_LDOUBLE_WORDS64 (hx, lx, x);
34 uhx = hx & 0x7fffffffffffffffULL;
35 int exponent = uhx >> (MANT_DIG - 1 - 64);
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 + MANT_DIG - 64)
46 {
47 /* Not necessarily an integer; integer bit is in low word.
48 Locate the bits with exponents 0 and -1. */
49 int int_pos = (BIAS + MANT_DIG - 1) - exponent;
50 int half_pos = int_pos - 1;
51 uint64_t half_bit = 1ULL << half_pos;
52 uint64_t int_bit = 1ULL << int_pos;
53 if ((lx & (int_bit | (half_bit - 1))) != 0)
54 {
55 /* Carry into the exponent works correctly. No need to test
56 whether HALF_BIT is set. */
57 lx += half_bit;
58 hx += lx < half_bit;
59 }
60 lx &= ~(int_bit - 1);
61 }
62 else if (exponent == BIAS + MANT_DIG - 65)
63 {
64 /* Not necessarily an integer; integer bit is bottom of high
65 word, half bit is top of low word. */
66 if (((hx & 1) | (lx & 0x7fffffffffffffffULL)) != 0)
67 {
68 lx += 0x8000000000000000ULL;
69 hx += lx < 0x8000000000000000ULL;
70 }
71 lx = 0;
72 }
73 else if (exponent >= BIAS)
74 {
75 /* At least 1; not necessarily an integer, integer bit and half
76 bit are in the high word. Locate the bits with exponents 0
77 and -1 (when the unbiased exponent is 0, the bit with
78 exponent 0 is implicit, but as the bias is odd it is OK to
79 take it from the low bit of the exponent). */
80 int int_pos = (BIAS + MANT_DIG - 65) - exponent;
81 int half_pos = int_pos - 1;
82 uint64_t half_bit = 1ULL << half_pos;
83 uint64_t int_bit = 1ULL << int_pos;
84 if (((hx & (int_bit | (half_bit - 1))) | lx) != 0)
85 hx += half_bit;
86 hx &= ~(int_bit - 1);
87 lx = 0;
88 }
89 else if (exponent == BIAS - 1 && (uhx > 0x3ffe000000000000ULL || lx != 0))
90 {
91 /* Interval (0.5, 1). */
92 hx = (hx & 0x8000000000000000ULL) | 0x3fff000000000000ULL;
93 lx = 0;
94 }
95 else
96 {
97 /* Rounds to 0. */
98 hx &= 0x8000000000000000ULL;
99 lx = 0;
100 }
101 SET_LDOUBLE_WORDS64 (x, hx, lx);
102 return x;
103}
104libm_alias_ldouble (__roundeven, roundeven)
105