ieee_handler(3M)        (BSD Compatibility Package)        ieee_handler(3M)

NAME
     ieeehandler - IEEE exception trap handler function

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

     #include <fp.h>

     int ieeehandler(action, exception, hdl)
     char action[], exception[];
     sigfpehandlertype hdl;

DESCRIPTION
     This function provides easy exception handling to exploit ANSI/IEEE
     Standard 754-1985 arithmetic in a C program. All arguments are
     pointers to strings. Results arising from invalid arguments and
     invalid combinations are undefined for efficiency.

     There are three types of action: "get", "set", and "clear". There are
     five types of exception:

          "inexact"
          "division"     ... division by zero exception

          "underflow"
          "overflow"
          "invalid"
          "all"          ... all five exceptions above

          "common"       ... invalid, overflow, and division exceptions

     The exceptions "all" and "common" only make sense with "set" or
     "clear".

     hdl contains the address of a signal-handling routine. <fp.h> defines
     sigfpehandlertype.

     "get will find the location of the current handler routine for
     exception in hdl. "set" will set the routine pointed at by hdl to be
     the handler routine and at the same time enable the trap on exception,
     except when hdl == SIGFPEDEFAULT or SIGFPEIGNORE; then ieeehandler
     will disable the trap on exception. When hdl == SIGFPEABORT, any trap
     on exception will dump core using abort(3C). "clear" "all" disables
     trapping on all five exceptions.

     Two steps are required to intercept an IEEE-related SIGFPE code with
     ieeehandler:

     1)  Set up a handler with ieeehandler.

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



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ieee_handler(3M)        (BSD Compatibility Package)        ieee_handler(3M)

     Unlike sigfpe, ieeehandler also adjusts floating-point hardware mode
     bits affecting IEEE trapping. The hardware trap is disabled when these
     actions are performed: "clear", "set" SIGFPEDEFAULT or "set"
     SIGFPEIGNORE.

     The hardware trap is enabled when any other "set" is used.

     SIGFPE signals can be handled using sigvec(3), signal(2), signal(3-ucb),
     sigfpe(3), or ieeehandler(3M). In a particular program, to avoid confu-
     sion, use only one of these interfaces to handle SIGFPE signals.

RETURN VALUE
     ieeehandler normally returns 0. In the case of set, 1 will be
     returned if the action is not available (for instance, not supported
     in hardware).

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);
     }

     and it might be set up like this:

     extern void samplehandler;
     main
     {
          sigfpehandlertype hdl, oldhandler1, oldhandler2;
     /*
     * save current overflow and invalid handlers
     */
          ieeehandler("get","overflow",oldhandler1);
          ieeehandler("get","invalid", oldhandler2);
     /*
     * set new overflow handler to samplehandler and set new
     * invalid handler to SIGFPEABORT (abort on invalid)
     */





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ieee_handler(3M)        (BSD Compatibility Package)        ieee_handler(3M)

          hdl = (sigfpehandlertype) samplehandler;
          if(ieeehandler("set","overflow",hdl) != 0)
               printf("ieeehandler can't set overflow \n");
          if(ieeehandler("set","invalid",SIGFPEABORT) != 0)
               printf("ieeehandler can't set invalid \n");
          ...
     /*
     * restore old overflow and invalid handlers
     */
          ieeehandler("set","overflow", oldhandler1);
          ieeehandler("set","invalid", oldhandler2);
     }

FILES
     /usr/include/fp.h

     /usr/include/signal.h

SEE ALSO
     signal(2), sigfpe(3), sigvec(3), signal(3-ucb), abort(3C),
     floatingpoint(3M).

































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