sortix--sortix/libm/man/feenableexcept.3

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.Dd March 16, 2005
.Dt FEENABLEEXCEPT 3
.Os
.Sh NAME
.Nm feenableexcept ,
.Nm fedisableexcept ,
.Nm fegetexcept
.Nd floating-point exception masking
.Sh LIBRARY
.Lb libm
.Sh SYNOPSIS
.In fenv.h
.Fd "#pragma STDC FENV_ACCESS ON"
.Ft int
.Fn feenableexcept "int excepts"
.Ft int
.Fn fedisableexcept "int excepts"
.Ft int
.Fn fegetexcept "void"
.Sh DESCRIPTION
The
.Fn feenableexcept
and
.Fn fedisableexcept
functions
unmask and mask (respectively) exceptions specified in
.Fa excepts .
The
.Fn fegetexcept
function
returns the current exception mask.
All exceptions are masked by default.
.Pp
Floating-point operations that produce unmasked exceptions will trap, and a
.Dv SIGFPE
will be delivered to the process.
By installing a signal handler for
.Dv SIGFPE ,
applications can take appropriate action immediately without
testing the exception flags after every operation.
Note that the trap may not be immediate, but it should occur
before the next floating-point instruction is executed.
.Pp
For all of these functions, the possible types of exceptions
include those described in
.Xr fenv 3 .
Some architectures may define other types of floating-point exceptions.
.Sh RETURN VALUES
The
.Fn feenableexcept ,
.Fn fedisableexcept ,
and
.Fn fegetexcept
functions return a bitmap of the exceptions that were unmasked
prior to the call.
.Sh SEE ALSO
.Xr sigaction 2 ,
.Xr feclearexcept 3 ,
.Xr feholdexcept 3 ,
.Xr fenv 3 ,
.Xr feupdateenv 3
.Sh BUGS
Functions in the standard library may trigger exceptions multiple
times as a result of intermediate computations;
however, they generally do not trigger spurious exceptions.
.Pp
No interface is provided to permit exceptions to be handled in
nontrivial ways.
There is no uniform way for an exception handler to access
information about the exception-causing instruction, or
to determine whether that instruction should be reexecuted
after returning from the handler.