Manual Pages for UNIX Operating System command usage for man feupdateenv

Mathematical Library Functions                    feupdateenv(3M)



NAME
     feupdateenv - update floating-point environment

SYNOPSIS
     c99 [ flag... ] file... -lm [ library... ]
     #include 

     int feupdateenv(const fenv_t *envp);


DESCRIPTION
     The feupdateenv() function attempts to  save  the  currently
     raised  floating-point  exceptions in its automatic storage,
     attempts   to   install   the   floating-point   environment
     represented  by  the  object  pointed  to  by envp, and then
     attempts to raise the saved floating-point  exceptions.  The
     envp  argument  points  to  an  object  set  by  a  call  to
     fegetenv(3M) or feholdexcept(3M), or equals a floating-point
     environment macro.

RETURN VALUES
     The feupdateenv() function returns 0 if and only if all  the
     required actions were successfully carried out.

ERRORS
     No errors are defined.

EXAMPLES
     The following  example  demonstrates  sample  code  to  hide
     spurious underflow floating-point exceptions:

     Example 1 Hide spurious underflow floating-point exceptions.

       #include 
       double f(double x)
       {
       #   pragma STDC FENV_ACCESS ON
           double result;
           fenv_t save_env;
           feholdexcept(&save_env);
           // compute result
           if (/* test spurious underflow */)
           feclearexcept(FE_UNDERFLOW);
           feupdateenv(&save_env);
           return result;
       }


ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:




SunOS 5.11          Last change: 12 Jul 2006                    1






Mathematical Library Functions                    feupdateenv(3M)



     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | Interface Stability         | Committed                   |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|
    | Standard                    | See standards(5).           |
    |_____________________________|_____________________________|


SEE ALSO
     fegetenv(3M),   feholdexcept(3M),   fenv.h(3HEAD),    attri-
     butes(5), standards(5)

NOTES
     In  a  multithreaded  program,  the  feupdateenv()  function
     affects  the floating point environment only for the calling
     thread.


     When the FEX_CUSTOM handling mode is in effect for an excep-
     tion,  raising that exception using feupdateenv() causes the
     handling function to be invoked. The handling  function  can
     then  modify  the  exception flags to be set as described in
     fex_set_handling(3M).  Any result value the handler supplies
     will be ignored.


     The feupdateenv() function automatically installs and  dein-
     stalls  SIGFPE  handlers and sets and clears the trap enable
     mode bits in the floating point status register  as  needed.
     If  a program uses these functions and attempts to install a
     SIGFPE handler or control the trap enable mode bits indepen-
     dently, the resulting behavior is not defined.


     As described in fex_set_handling(3M), when a handling  func-
     tion  installed in FEX_CUSTOM mode is invoked, all exception
     traps are disabled (and will not be reenabled  while  SIGFPE
     is blocked). Thus, attempting to change the environment from
     within a handler  by  calling  fesetenv(3M)  or  feupdateenv
     might not produce the expected results.












SunOS 5.11          Last change: 12 Jul 2006                    2