sigfpe(3)              C LIBRARY FUNCTIONS              sigfpe(3)



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:
    FPEFLTINEXTRAP    fp_inexact     floating inexact result
    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
     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 compi-
     lation  option -ffpa causes fpa recomputation to replace the
     default  abort  action  for   code   FPEFPAERROR.    Note:
     SIGFPEDEFAULT will restore abort rather than FPA recomputa-
     tion 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 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.




             Last change: BSD Compatibility Package             1

sigfpe(3)              C LIBRARY FUNCTIONS              sigfpe(3)



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);
                     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.







             Last change: BSD Compatibility Package             2