1 | /* Round to nearest integer value, rounding halfway cases to even. |
2 | ldbl-96 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 64 |
26 | #define MAX_EXP (2 * BIAS + 1) |
27 | |
28 | long double |
29 | roundevenl (long double x) |
30 | { |
31 | uint16_t se; |
32 | uint32_t hx, lx; |
33 | GET_LDOUBLE_WORDS (se, hx, lx, x); |
34 | int exponent = se & 0x7fff; |
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 - 32) |
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 | uint32_t half_bit = 1U << half_pos; |
51 | uint32_t int_bit = 1U << int_pos; |
52 | if ((lx & (int_bit | (half_bit - 1))) != 0) |
53 | { |
54 | /* No need to test whether HALF_BIT is set. */ |
55 | lx += half_bit; |
56 | if (lx < half_bit) |
57 | { |
58 | hx++; |
59 | if (hx == 0) |
60 | { |
61 | hx = 0x80000000; |
62 | se++; |
63 | } |
64 | } |
65 | } |
66 | lx &= ~(int_bit - 1); |
67 | } |
68 | else if (exponent == BIAS + MANT_DIG - 33) |
69 | { |
70 | /* Not necessarily an integer; integer bit is bottom of high |
71 | word, half bit is top of low word. */ |
72 | if (((hx & 1) | (lx & 0x7fffffff)) != 0) |
73 | { |
74 | lx += 0x80000000; |
75 | if (lx < 0x80000000) |
76 | { |
77 | hx++; |
78 | if (hx == 0) |
79 | { |
80 | hx = 0x80000000; |
81 | se++; |
82 | } |
83 | } |
84 | } |
85 | lx = 0; |
86 | } |
87 | else if (exponent >= BIAS) |
88 | { |
89 | /* At least 1; not necessarily an integer, integer bit and half |
90 | bit are in the high word. Locate the bits with exponents 0 |
91 | and -1. */ |
92 | int int_pos = (BIAS + MANT_DIG - 33) - exponent; |
93 | int half_pos = int_pos - 1; |
94 | uint32_t half_bit = 1U << half_pos; |
95 | uint32_t int_bit = 1U << int_pos; |
96 | if (((hx & (int_bit | (half_bit - 1))) | lx) != 0) |
97 | { |
98 | hx += half_bit; |
99 | if (hx < half_bit) |
100 | { |
101 | hx = 0x80000000; |
102 | se++; |
103 | } |
104 | } |
105 | hx &= ~(int_bit - 1); |
106 | lx = 0; |
107 | } |
108 | else if (exponent == BIAS - 1 && (hx > 0x80000000 || lx != 0)) |
109 | { |
110 | /* Interval (0.5, 1). */ |
111 | se = (se & 0x8000) | 0x3fff; |
112 | hx = 0x80000000; |
113 | lx = 0; |
114 | } |
115 | else |
116 | { |
117 | /* Rounds to 0. */ |
118 | se &= 0x8000; |
119 | hx = 0; |
120 | lx = 0; |
121 | } |
122 | SET_LDOUBLE_WORDS (x, se, hx, lx); |
123 | return x; |
124 | } |
125 | |