1feupdateenv(3M)         Mathematical Library Functions         feupdateenv(3M)
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NAME

6       feupdateenv - update floating-point environment
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SYNOPSIS

9       c99 [ flag... ] file... -lm [ library... ]
10       #include <fenv.h>
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12       int feupdateenv(const fenv_t *envp);
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DESCRIPTION

16       The feupdateenv() function attempts to save the currently raised float‐
17       ing-point exceptions in its automatic storage, attempts to install  the
18       floating-point  environment  represented  by  the  object pointed to by
19       envp, and then attempts to raise the saved  floating-point  exceptions.
20       The  envp argument points to an object set by a call to fegetenv(3M) or
21       feholdexcept(3M), or equals a floating-point environment macro.
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RETURN VALUES

24       The feupdateenv() function returns 0 if and only if  all  the  required
25       actions were successfully carried out.
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ERRORS

28       No errors are defined.
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EXAMPLES

31       The  following example demonstrates sample code to hide spurious under‐
32       flow floating-point exceptions:
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34       Example 1 Hide spurious underflow floating-point exceptions.
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36         #include <fenv.h>
37         double f(double x)
38         {
39         #   pragma STDC FENV_ACCESS ON
40             double result;
41             fenv_t save_env;
42             feholdexcept(&save_env);
43             // compute result
44             if (/* test spurious underflow */)
45             feclearexcept(FE_UNDERFLOW);
46             feupdateenv(&save_env);
47             return result;
48         }
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ATTRIBUTES

52       See attributes(5) for descriptions of the following attributes:
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57       ┌─────────────────────────────┬─────────────────────────────┐
58       │      ATTRIBUTE TYPE         │      ATTRIBUTE VALUE        │
59       ├─────────────────────────────┼─────────────────────────────┤
60       │Interface Stability          │Standard                     │
61       ├─────────────────────────────┼─────────────────────────────┤
62       │MT-Level                     │MT-Safe                      │
63       └─────────────────────────────┴─────────────────────────────┘
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SEE ALSO

66       fegetenv(3M),  feholdexcept(3M),  fenv.h(3HEAD),  attributes(5),  stan‐
67       dards(5)
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NOTES

70       In  a  multithreaded  program,  the  feupdateenv() function affects the
71       floating point environment only for the calling thread.
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74       When the FEX_CUSTOM handling mode is in effect for an exception,  rais‐
75       ing  that exception using feupdateenv() causes the handling function to
76       be invoked. The handling function can then modify the  exception  flags
77       to  be  set as described in fex_set_handling(3M).  Any result value the
78       handler supplies will be ignored.
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81       The feupdateenv() function automatically installs and deinstalls SIGFPE
82       handlers  and sets and clears the trap enable mode bits in the floating
83       point status register as needed. If a program uses these functions  and
84       attempts  to  install  a SIGFPE handler or control the trap enable mode
85       bits independently, the resulting behavior is not defined.
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88       As  described  in  fex_set_handling(3M),  when  a   handling   function
89       installed  in  FEX_CUSTOM mode is invoked, all exception traps are dis‐
90       abled (and will not  be  reenabled  while  SIGFPE  is  blocked).  Thus,
91       attempting  to  change the environment from within a handler by calling
92       fesetenv(3M) or feupdateenv might not produce the expected results.
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96SunOS 5.11                        12 Jul 2006                  feupdateenv(3M)
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