1 | /* |
---|
2 | * ==================================================== |
---|
3 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. |
---|
4 | * |
---|
5 | * Developed at SunPro, a Sun Microsystems, Inc. business. |
---|
6 | * Permission to use, copy, modify, and distribute this |
---|
7 | * software is freely granted, provided that this notice |
---|
8 | * is preserved. |
---|
9 | * ==================================================== |
---|
10 | */ |
---|
11 | /* |
---|
12 | FUNCTION |
---|
13 | <<trunc>>, <<truncf>>---round to integer, towards zero |
---|
14 | INDEX |
---|
15 | trunc |
---|
16 | INDEX |
---|
17 | truncf |
---|
18 | |
---|
19 | SYNOPSIS |
---|
20 | #include <math.h> |
---|
21 | double trunc(double <[x]>); |
---|
22 | float truncf(float <[x]>); |
---|
23 | |
---|
24 | DESCRIPTION |
---|
25 | The <<trunc>> functions round their argument to the integer value, in |
---|
26 | floating format, nearest to but no larger in magnitude than the |
---|
27 | argument, regardless of the current rounding direction. (While the |
---|
28 | "inexact" floating-point exception behavior is unspecified by the C |
---|
29 | standard, the <<trunc>> functions are written so that "inexact" is not |
---|
30 | raised if the result does not equal the argument, which behavior is as |
---|
31 | recommended by IEEE 754 for its related functions.) |
---|
32 | |
---|
33 | RETURNS |
---|
34 | <[x]> truncated to an integral value. |
---|
35 | |
---|
36 | PORTABILITY |
---|
37 | ANSI C, POSIX |
---|
38 | |
---|
39 | */ |
---|
40 | |
---|
41 | #include "fdlibm.h" |
---|
42 | |
---|
43 | #ifndef _DOUBLE_IS_32BITS |
---|
44 | |
---|
45 | #ifdef __STDC__ |
---|
46 | double trunc(double x) |
---|
47 | #else |
---|
48 | double trunc(x) |
---|
49 | double x; |
---|
50 | #endif |
---|
51 | { |
---|
52 | int signbit; |
---|
53 | /* Most significant word, least significant word. */ |
---|
54 | int msw; |
---|
55 | unsigned int lsw; |
---|
56 | int exponent_less_1023; |
---|
57 | |
---|
58 | EXTRACT_WORDS(msw, lsw, x); |
---|
59 | |
---|
60 | /* Extract sign bit. */ |
---|
61 | signbit = msw & 0x80000000; |
---|
62 | |
---|
63 | /* Extract exponent field. */ |
---|
64 | exponent_less_1023 = ((msw & 0x7ff00000) >> 20) - 1023; |
---|
65 | |
---|
66 | if (exponent_less_1023 < 20) |
---|
67 | { |
---|
68 | /* All significant digits are in msw. */ |
---|
69 | if (exponent_less_1023 < 0) |
---|
70 | { |
---|
71 | /* -1 < x < 1, so result is +0 or -0. */ |
---|
72 | INSERT_WORDS(x, signbit, 0); |
---|
73 | } |
---|
74 | else |
---|
75 | { |
---|
76 | /* All relevant fraction bits are in msw, so lsw of the result is 0. */ |
---|
77 | INSERT_WORDS(x, signbit | (msw & ~(0x000fffff >> exponent_less_1023)), 0); |
---|
78 | } |
---|
79 | } |
---|
80 | else if (exponent_less_1023 > 51) |
---|
81 | { |
---|
82 | if (exponent_less_1023 == 1024) |
---|
83 | { |
---|
84 | /* x is infinite, or not a number, so trigger an exception. */ |
---|
85 | return x + x; |
---|
86 | } |
---|
87 | /* All bits in the fraction fields of the msw and lsw are needed in the result. */ |
---|
88 | } |
---|
89 | else |
---|
90 | { |
---|
91 | /* All fraction bits in msw are relevant. Truncate irrelevant |
---|
92 | bits from lsw. */ |
---|
93 | INSERT_WORDS(x, msw, lsw & ~(0xffffffffu >> (exponent_less_1023 - 20))); |
---|
94 | } |
---|
95 | return x; |
---|
96 | } |
---|
97 | |
---|
98 | #endif /* _DOUBLE_IS_32BITS */ |
---|