sigfpe(3BSD)         (BSD System Compatibility)         sigfpe(3BSD)


       NAME
             sigfpe - (BSD) signal handling for specific SIGFPE codes

       SYNOPSIS
             /usr/ucb/cc [flag . . . ] file . . .
             #include <signal.h>
             #include <fp.h>
             sigfpe_handler_type sigfpe(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(3C), 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(3BSD).

             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 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.



                           Copyright 1994 Novell, Inc.               Page 1

      sigfpe(3BSD)         (BSD System Compatibility)         sigfpe(3BSD)


            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(3BSD), 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(3BSD),
            signal(3BSD), sigfpe(3BSD), or ieee_handler(3BSD).  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)


                          Copyright 1994 Novell, Inc.               Page 2

       sigfpe(3BSD)         (BSD System Compatibility)         sigfpe(3BSD)


                      */
                             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);
                     }

       FILES
             /usr/ucbinclude/fp.h
             /usr/ucbinclude/signal.h

       REFERENCES
             abort(3C), floatingpoint(3BSD), ieee_handler(3BSD),
             signal(3BSD), sigvec(3BSD)

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

























                           Copyright 1994 Novell, Inc.               Page 3