1/* Round to nearest integer value, rounding halfway cases to even.
2 ldbl-128 version.
3 Copyright (C) 2016-2017 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 <stdint.h>
23
24#define BIAS 0x3fff
25#define MANT_DIG 113
26#define MAX_EXP (2 * BIAS + 1)
27
28_Float128
29roundevenl (_Float128 x)
30{
31 uint64_t hx, lx, uhx;
32 GET_LDOUBLE_WORDS64 (hx, lx, x);
33 uhx = hx & 0x7fffffffffffffffULL;
34 int exponent = uhx >> (MANT_DIG - 1 - 64);
35 if (exponent >= BIAS + MANT_DIG - 1)
36 {
37 /* Integer, infinity or NaN. */
38 if (exponent == MAX_EXP)
39 /* Infinity or NaN; quiet signaling NaNs. */
40 return x + x;
41 else
42 return x;
43 }
44 else if (exponent >= BIAS + MANT_DIG - 64)
45 {
46 /* Not necessarily an integer; integer bit is in low word.
47 Locate the bits with exponents 0 and -1. */
48 int int_pos = (BIAS + MANT_DIG - 1) - exponent;
49 int half_pos = int_pos - 1;
50 uint64_t half_bit = 1ULL << half_pos;
51 uint64_t int_bit = 1ULL << int_pos;
52 if ((lx & (int_bit | (half_bit - 1))) != 0)
53 {
54 /* Carry into the exponent works correctly. No need to test
55 whether HALF_BIT is set. */
56 lx += half_bit;
57 hx += lx < half_bit;
58 }
59 lx &= ~(int_bit - 1);
60 }
61 else if (exponent == BIAS + MANT_DIG - 65)
62 {
63 /* Not necessarily an integer; integer bit is bottom of high
64 word, half bit is top of low word. */
65 if (((hx & 1) | (lx & 0x7fffffffffffffffULL)) != 0)
66 {
67 lx += 0x8000000000000000ULL;
68 hx += lx < 0x8000000000000000ULL;
69 }
70 lx = 0;
71 }
72 else if (exponent >= BIAS)
73 {
74 /* At least 1; not necessarily an integer, integer bit and half
75 bit are in the high word. Locate the bits with exponents 0
76 and -1 (when the unbiased exponent is 0, the bit with
77 exponent 0 is implicit, but as the bias is odd it is OK to
78 take it from the low bit of the exponent). */
79 int int_pos = (BIAS + MANT_DIG - 65) - exponent;
80 int half_pos = int_pos - 1;
81 uint64_t half_bit = 1ULL << half_pos;
82 uint64_t int_bit = 1ULL << int_pos;
83 if (((hx & (int_bit | (half_bit - 1))) | lx) != 0)
84 hx += half_bit;
85 hx &= ~(int_bit - 1);
86 lx = 0;
87 }
88 else if (exponent == BIAS - 1 && (uhx > 0x3ffe000000000000ULL || lx != 0))
89 {
90 /* Interval (0.5, 1). */
91 hx = (hx & 0x8000000000000000ULL) | 0x3fff000000000000ULL;
92 lx = 0;
93 }
94 else
95 {
96 /* Rounds to 0. */
97 hx &= 0x8000000000000000ULL;
98 lx = 0;
99 }
100 SET_LDOUBLE_WORDS64 (x, hx, lx);
101 return x;
102}
103