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11 .TH feupdateenv 3M "12 Jul 2006" "SunOS 5.11" "Mathematical Library Functions"
12 .SH NAME
13 feupdateenv \- update floating-point environment
14 .SH SYNOPSIS
15 .LP
16 .nf
17 c99 [ \fIflag\fR... ] \fIfile\fR... \fB-lm\fR [ \fIlibrary\fR... ]
18 #include <fenv.h>
19
20 \fBint\fR \fBfeupdateenv\fR(\fBconst fenv_t *\fR\fIenvp\fR);
21 .fi
22
23 .SH DESCRIPTION
24 .sp
25 .LP
26 The \fBfeupdateenv()\fR function attempts to save the currently raised
27 floating-point exceptions in its automatic storage, attempts to install the
28 floating-point environment represented by the object pointed to by \fIenvp\fR,
29 and then attempts to raise the saved floating-point exceptions. The \fIenvp\fR
30 argument points to an object set by a call to \fBfegetenv\fR(3M) or
31 \fBfeholdexcept\fR(3M), or equals a floating-point environment macro.
32 .SH RETURN VALUES
33 .sp
34 .LP
35 The \fBfeupdateenv()\fR function returns 0 if and only if all the required
36 actions were successfully carried out.
37 .SH ERRORS
38 .sp
39 .LP
40 No errors are defined.
41 .SH EXAMPLES
42 .sp
43 .LP
44 The following example demonstrates sample code to hide spurious underflow
45 floating-point exceptions:
46 .LP
47 \fBExample 1 \fRHide spurious underflow floating-point exceptions.
48 .sp
49 .in +2
50 .nf
51 #include <fenv.h>
52 double f(double x)
53 {
54 # pragma STDC FENV_ACCESS ON
55 double result;
56 fenv_t save_env;
57 feholdexcept(&save_env);
58 // compute result
59 if (/* test spurious underflow */)
60 feclearexcept(FE_UNDERFLOW);
61 feupdateenv(&save_env);
62 return result;
63 }
64 .fi
65 .in -2
66
67 .SH ATTRIBUTES
68 .sp
69 .LP
70 See \fBattributes\fR(5) for descriptions of the following attributes:
71 .sp
72
73 .sp
74 .TS
75 tab() box;
76 cw(2.75i) |cw(2.75i)
77 lw(2.75i) |lw(2.75i)
78 .
79 ATTRIBUTE TYPEATTRIBUTE VALUE
80 _
81 Interface StabilityStandard
82 _
83 MT-LevelMT-Safe
84 .TE
85
86 .SH SEE ALSO
87 .sp
88 .LP
89 \fBfegetenv\fR(3M), \fBfeholdexcept\fR(3M), \fBfenv.h\fR(3HEAD),
90 \fBattributes\fR(5), \fBstandards\fR(5)
91 .SH NOTES
92 .sp
93 .LP
94 In a multithreaded program, the \fBfeupdateenv()\fR function affects the
95 floating point environment only for the calling thread.
96 .sp
97 .LP
98 When the \fBFEX_CUSTOM\fR handling mode is in effect for an exception, raising
99 that exception using \fBfeupdateenv()\fR causes the handling function to be
100 invoked. The handling function can then modify the exception flags to be set as
101 described in \fBfex_set_handling\fR(3M). Any result value the handler supplies
102 will be ignored.
103 .sp
104 .LP
105 The \fBfeupdateenv()\fR function automatically installs and deinstalls
106 \fBSIGFPE\fR handlers and sets and clears the trap enable mode bits in the
107 floating point status register as needed. If a program uses these functions and
108 attempts to install a \fBSIGFPE\fR handler or control the trap enable mode bits
109 independently, the resulting behavior is not defined.
110 .sp
111 .LP
112 As described in \fBfex_set_handling\fR(3M), when a handling function installed
113 in \fBFEX_CUSTOM\fR mode is invoked, all exception traps are disabled (and will
114 not be reenabled while \fBSIGFPE\fR is blocked). Thus, attempting to change the
115 environment from within a handler by calling \fBfesetenv\fR(3M) or
116 \fBfeupdateenv\fR might not produce the expected results.