sigfpe(3)               (BSD Compatibility Package)               sigfpe(3)

NAME
     sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS
     /usr/ucb/cc [flag ...] file ... -lucb

     #include <signal.h>
     #include <floatingpoint.h>

     sigfpehandlertype sigfpe(code, hdl)
     sigfpecodetype code;
     sigfpehandlertype 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 partic-
     ular SIGFPE code and returns the old handler as the value of the func-
     tion sigfpe. Normally handlers are specified as pointers to functions;
     the special cases SIGFPEIGNORE, SIGFPEABORT, and SIGFPEDEFAULT
     allow ignoring, specifying core dump using abort, or default handling
     respectively.

     For these IEEE-related codes:

         FPEFLTINEXTRAP    fpinexact     floating inexact result
         FPEFLTDIVTRAP     fpdivision    floating division by zero
         FPEFLTUNDTRAP     fpunderflow   floating underflow
         FPEFLTOVFTRAP     fpoverflow    floating overflow
         FPEFLTBSUNTRAP    fpinvalid     branch or set on unordered
         FPEFLTOPERRTRAP   fpinvalid     floating operand error
         FPEFLTNANTRAP     fpinvalid     floating Not-A-Number

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

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

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














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sigfpe(3)               (BSD Compatibility Package)               sigfpe(3)

     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 ieeehandler(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(3), signal(3-ucb),
     sigfpe(3), or ieeehandler(3M). In a particular program, to avoid con-
     fusion, use only one of these interfaces to handle SIGFPE signals.

EXAMPLES
     A user-specified signal handler might look like this:

     void samplehandler( 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->scpc);
          }


















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sigfpe(3)               (BSD Compatibility Package)               sigfpe(3)

     It might be set up like this:

          extern void samplehandler;
          main
          {
            sigfpehandlertype hdl, oldhandler1, oldhandler2;
          /*
           * save current overflow and invalid handlers; set the new
           * overflow handler to samplehandler and set the new
           * invalid handler to SIGFPEABORT (abort on invalid)
           */
            hdl = (sigfpehandlertype) samplehandler;
            oldhandler1 = sigfpe(FPEFLTOVFTRAP, hdl);
            oldhandler2 = sigfpe(FPEFLTOPERRTRAP, SIGFPEABORT);
            ...
          /*
           * restore old overflow and invalid handlers
           */
            sigfpe(FPEFLTOVFTRAP,   oldhandler1);
            sigfpe(FPEFLTOPERRTRAP, oldhandler2);
          }

RETURN VALUE
     sigfpe returns BADSIG if code is not zero or a defined SIGFPE code.

FILES
     /usr/include/floatingpoint.h

     /usr/include/signal.h

SEE ALSO
     sigvec(3), signal(3-ucb), abort(3C), floatingpoint(3M),
     ieeehandler(3M), signal(5).





















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