'\" te
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.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
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.TH sigfpe 3C "4 May 2004" "SunOS 5.11" "Standard C Library Functions"
.SH NAME
sigfpe \- signal handling for specific SIGFPE codes
.SH SYNOPSIS
.LP
.nf
#include <floatingpoint.h>
#include <siginfo.h>

\fBsigfpe_handler_type\fR \fBsigfpe\fR(\fBsigfpe_code_type\fR \fIcode\fR,
     \fBsigfpe_handler_type\fR \fIhdl\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBsigfpe()\fR function allows signal handling to be specified for
particular \fBSIGFPE\fR codes.  A call to \fBsigfpe()\fR defines a new handler
\fIhdl\fR for a particular \fBSIGFPE\fR \fIcode\fR and returns the old handler
as the value of the function \fBsigfpe()\fR. Normally handlers are specified as
pointers to functions; the special cases \fBSIGFPE_IGNORE\fR,
\fBSIGFPE_ABORT\fR, and \fBSIGFPE_DEFAULT\fR allow ignoring, dumping core using
\fBabort\fR(3C), or default handling respectively. Default handling is to dump
core using \fBabort\fR(3C).
.sp
.LP
The \fIcode\fR argument is usually one of the five \fBIEEE\|754-related\fR
\fBSIGFPE\fR codes:
.sp
.in +2
.nf
FPE_FLTRES   fp_inexact \(mi floating-point inexact result
FPE_FLTDIV   fp_division \(mi floating-point division by zero        
FPE_FLTUND   fp_underflow \(mi floating-point underflow
FPE_FLTOVF   fp_overflow \(mi floating-point overflow
FPE_FLTINV   fp_invalid \(mi floating-point invalid operation
.fi
.in -2

.sp
.LP
Three steps are required to intercept an \fBIEEE\|754-related\fR \fBSIGFPE\fR
code with \fBsigfpe()\fR:
.RS +4
.TP
1.
Set up a handler with \fBsigfpe()\fR.
.RE
.RS +4
.TP
2.
Enable the relevant \fBIEEE\|754\fR trapping capability in the hardware,
perhaps by using assembly-language instructions.
.RE
.RS +4
.TP
3.
Perform a floating-point operation that generates the intended
\fBIEEE\|754\fR exception.
.RE
.sp
.LP
The \fBsigfpe()\fR function never changes floating-point hardware mode bits
affecting \fBIEEE\|754\fR trapping.  No \fBIEEE\|754-related\fR \fBSIGFPE\fR
signals will be generated unless those hardware mode bits are enabled.
.sp
.LP
\fBSIGFPE\fR signals can be handled using \fBsigfpe()\fR, \fBsigaction\fR(2) or
\fBsignal\fR(3C). In a particular program, to avoid confusion, use only one of
these interfaces to handle \fBSIGFPE\fR signals.
.SH EXAMPLES
.LP
\fBExample 1 \fRExample Of A User-Specified Signal Handler
.sp
.LP
A user-specified signal handler might look like this:

.sp
.in +2
.nf
#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
/*
* The sample_handler prints out a message then commits suicide.
*/
void
sample_handler(int sig, siginfo_t *sip, ucontext_t *uap) {
	char *label;
        switch (sip\(mi>si_code) {
	case FPE_FLTINV: label = "invalid operand"; break;
	case FPE_FLTRES: label = "inexact"; break;
	case FPE_FLTDIV: label = "division-by-zero"; break;
	case FPE_FLTUND: label = "underflow"; break;
	case FPE_FLTOVF: label = "overflow"; break;
	default: label = "???"; break;
	}
	fprintf(stderr, 
        "FP exception %s (0x%x) occurred at address %p.\en",
        label, sip\(mi>si_code, (void *) sip\(mi>si_addr);
	abort();
}
.fi
.in -2

.sp
.LP
and it might be set up like this:

.sp
.in +2
.nf
#include <floatingpoint.h>
#include <siginfo.h>
#include <ucontext.h>
extern void sample_handler(int, siginfo_t *, ucontext_t *);
main(void) {
      sigfpe_handler_type hdl, old_handler1, old_handler2;
/*
 * save current fp_overflow and fp_invalid handlers; set the new
* fp_overflow handler to sample_handler(\|) and set the new
* fp_invalid handler to SIGFPE_ABORT (abort on invalid)
*/
    hdl = (sigfpe_handler_type) sample_handler;
    old_handler1 = sigfpe(FPE_FLTOVF, hdl);
    old_handler2 = sigfpe(FPE_FLTINV, SIGFPE_ABORT);
    .\|.\|.
/*
 * restore old fp_overflow and fp_invalid handlers
 */
     sigfpe(FPE_FLTOVF, old_handler1);
     sigfpe(FPE_FLTINV, old_handler2);
}
.fi
.in -2

.SH FILES
.sp
.ne 2
.mk
.na
\fB\fB/usr/include/floatingpoint.h\fR\fR
.ad
.sp .6
.RS 4n

.RE

.sp
.ne 2
.mk
.na
\fB\fB/usr/include/siginfo.h\fR\fR
.ad
.sp .6
.RS 4n

.RE

.SH ATTRIBUTES
.sp
.LP
See \fBattributes\fR(5) for descriptions of the following attributes:
.sp

.sp
.TS
tab() box;
cw(2.75i) |cw(2.75i) 
lw(2.75i) |lw(2.75i) 
.
ATTRIBUTE TYPEATTRIBUTE VALUE
_
MT-LevelSafe
.TE

.SH SEE ALSO
.sp
.LP
\fBsigaction\fR(2), \fBabort\fR(3C), \fBsignal\fR(3C), \fBattributes\fR(5),
\fBfloatingpoint.h\fR(3HEAD)
.SH DIAGNOSTICS
.sp
.LP
The \fBsigfpe()\fR function returns (void(*)())-1 if \fIcode\fR is not zero or
a defined \fBSIGFPE\fR code.