SIGFPE(3)

NAME
sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS
#include <signal.h>

#include <floatingpoint.h>

sigfpe_handler_type sigfpe(code, hdl)
sigfpe_code_type code;
sigfpe_handler_type hdl;

DESCRIPTION

This function allows signal handling to be specified for particular SIGFPE codes. A call to sigfpe() defines a new handler hdl for a particular SIGFPE code and returns the old handler as the value of the function sigfpe() . Normally handlers are specified as pointers to functions; the special cases SIGFPE_IGNORE, SIGFPE_ABORT, and SIGFPE_DEFAULT allow ignoring, specifying core dump using abort(3), or default handling respectively.

For these IEEE-related codes:
	FPE_FLTINEX_TRAP	fp_inexact - floating inexact result
	FPE_FLTDIV_TRAP	fp_division - floating division by zero
	FPE_FLTUND_TRAP	fp_underflow - floating underflow
	FPE_FLTOVF_TRAP	fp_overflow - floating overflow
	FPE_FLTBSUN_TRAP	fp_invalid - branch or set on unordered
	FPE_FLTOPERR_TRAP	fp_invalid - floating operand error
	FPE_FLTNAN_TRAP	fp_invalid - floating Not-A-Number

default handling is defined to be to call the handler specified to ieee_handler(3M).

For all other SIGFPE codes, default handling is to core dump using abort(3).

The compilation option -ffpa causes fpa recomputation to replace the default abort action for code FPE_FPA_ERROR. Note: SIGFPE_DEFAULT will restore abort rather than FPA recomputation for this code.

Three steps are required to intercept an IEEE-related SIGFPE code with sigfpe():

    1)  Set up a handler with sigfpe().

    2)  Enable the relevant IEEE trapping capability in the hardware, perhaps by using assembly-language instructions.

    3)  Perform a floating-point operation that generates the intended IEEE exception.

Unlike ieee_handler(3M), sigfpe() never changes floating-point hardware mode bits affecting IEEE trapping. No IEEE-related SIGFPE signals will be generated unless those hardware mode bits are enabled.

SIGFPE signals can be handled using sigvec(2), signal(3V), sigfpe(3), or ieee_handler(3M). In a particular program, to avoid confusion, use only one of these interfaces to handle SIGFPE signals.

EXAMPLE

A user-specified signal handler might look like this:
void sample_handler( sig, code, scp, addr )
	int sig ;		/* sig == SIGFPE always */
	int code ;
	struct sigcontext *scp ;
	char *addr ;
	{
		/*
		   Sample user-written sigfpe code handler.
		   Prints a message and continues.
		   struct sigcontext is defined in <signal.h>.
		 */
		printf(" ieee exception code %x occurred at pc %X \n",code,scp->sc_pc);
	}

and it might be set up like this:
	extern void sample_handler();
 	main()
	{
		sigfpe_handler_type hdl, old_handler1, old_handler2;
	/*
	 * save current overflow and invalid handlers; set the new
	 * overflow handler to sample_handler() and set the new
	 * invalid handler to SIGFPE_ABORT (abort on invalid)
	 */
		hdl = (sigfpe_handler_type) sample_handler;
		old_handler1 = sigfpe(FPE_FLTOVF_TRAP, hdl);
		old_handler2 = sigfpe(FPE_FLTOPERR_TRAP, SIGFPE_ABORT);
		...
	/*
	 * restore old overflow and invalid handlers
	 */
		sigfpe(FPE_FLTOVF_TRAP,   old_handler1);
		sigfpe(FPE_FLTOPERR_TRAP, old_handler2);
	}

SEE ALSO
sigvec(2), abort(3), floatingpoint(3), ieee_handler(3M), signal(3V)

DIAGNOSTICS

sigfpe() returns BADSIG if code is not zero or a defined SIGFPE code.