sigfpe(3-BSD)     MISC. REFERENCE MANUAL PAGES      sigfpe(3-BSD)



NAME
     sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS
     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 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  SIGFPEIGNORE, SIGFPEABORT, and SIGFPEDEFAULT allow
     ignoring, specifying core dump using  abort(3),  or  default
     handling respectively.

     For these IEEE-related codes:

    FPEFLTDIVTRAP     fp_division    floating division by zero
    FPEFLTUNDTRAP     fp_underflow   floating underflow
    FPEFLTOVFTRAP     fp_overflow    floating overflow
    FPEFLTBSUNTRAP    fp_invalid     branch or set on unordered
    FPEFLTOPERRTRAP   fp_invalid     floating operand error
    FPEFLTNANTRAP     fp_invalid     floating Not-A-Number
    FPEFLTINEXTRAP    fp_inexact     floating inexact result

     default handling is defined to be to call the handler speci-
     fied to ieeehandler(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 FPEFPAERROR.
     Note:  SIGFPEDEFAULT 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



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               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(2),  signal(3),
     sigfpe(3), or ieeehandler(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 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);
             }

     and 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);



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                     sigfpe(FPEFLTOPERRTRAP, oldhandler2);
             }

FILES
     /usr/include/floatingpoint.h
     /usr/include/signal.h

SEE ALSO
     sigvec(2), floatingpoint(3), ieeehandler(3M), signal(3),

     abort(3C) in the Programmer's Reference Manual.

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








































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