ieee_handler(3M)   UNIX System V(BSD Compatibility Package)    ieee_handler(3M)


NAME
      ieee_handler - IEEE exception trap handler function

SYNOPSIS
      cc [ flag. . . ] file . . . -lucb

      #include <fp.h>

      int ieee_handler(action,exception,hdl)
      char action[], exception[];
      sigfpe_handler_type hdl;

DESCRIPTION
      This function provides easy exception handling to exploit ANSI/IEEE Std
      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

      Note: all and common only make sense with set or clear

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

      get will get 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 == SIGFPE_DEFAULT or SIGFPE_IGNORE; then ieee_handler will disable
      the trap on exception.  When hdl == SIGFPE_ABORT, any trap on exception
      will dump core using abort(3).  clear all disables trapping on all five
      exceptions.

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

      1)    Set up a handler with ieee_handler.

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

      Unlike sigfpe(3), ieee_handler also adjusts floating-point hardware mode
      bits affecting IEEE trapping.  For clear, set SIGFPE_DEFAULT, or set
      SIGFPE_IGNORE, the hardware trap is disabled.  For any other set, the


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ieee_handler(3M)   UNIX System V(BSD Compatibility Package)    ieee_handler(3M)


      hardware trap is enabled.

      SIGFPE signals can be handled using sigvec(2), signal(3), signal(3F),
      sigfpe(3), or ieee_handler(3M).  In a particular program, to avoid
      confusion, use only one of these interfaces to handle SIGFPE signals.

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

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
            */
                  ieee_handler("get","overflow",old_handler1);
                  ieee_handler("get","invalid", old_handler2);
            /*
            * set new overflow handler to sample_handler and set new
            * invalid handler to SIGFPE_ABORT (abort on invalid)
            */
                  hdl = (sigfpe_handler_type) sample_handler;
                  if(ieee_handler("set","overflow",hdl) != 0)
                        printf("ieee_handler can't set overflow \n");
                  if(ieee_handler("set","invalid",SIGFPE_ABORT) != 0)
                        printf("ieee_handler can't set invalid \n");
                  ...
            /*
            * restore old overflow and invalid handlers
            */
                  ieee_handler("set","overflow", old_handler1);
                  ieee_handler("set","invalid", old_handler2);


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ieee_handler(3M)   UNIX System V(BSD Compatibility Package)    ieee_handler(3M)


            }

FILES
      /usr/include/fp.h
      /usr/include/signal.h

SEE ALSO
      floatingpoint(3), ieee_handler(3), sigfpe(3), signal(3) sigvec(3),
      signal(2), abort(3C) in the Programmer's Reference Manual













































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