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41c67149 JM |
1 | /* Round to nearest integer value, rounding halfway cases to even. |
2 | ldbl-128 version. | |
d614a753 | 3 | Copyright (C) 2016-2020 Free Software Foundation, Inc. |
41c67149 JM |
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 | |
5a82c748 | 18 | <https://www.gnu.org/licenses/>. */ |
41c67149 JM |
19 | |
20 | #include <math.h> | |
21 | #include <math_private.h> | |
fd3b4e7c | 22 | #include <libm-alias-ldouble.h> |
41c67149 JM |
23 | #include <stdint.h> |
24 | ||
25 | #define BIAS 0x3fff | |
26 | #define MANT_DIG 113 | |
27 | #define MAX_EXP (2 * BIAS + 1) | |
28 | ||
29 | _Float128 | |
01f28812 | 30 | __roundevenl (_Float128 x) |
41c67149 JM |
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 | } | |
fd3b4e7c | 104 | libm_alias_ldouble (__roundeven, roundeven) |