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 argu-
ments are pointers to strings.  Results arising from invalid
arguments  and  invalid combinations are undefined for effi-
ciency.  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 excep-
tion 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 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);
     }

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 Refer-
ence Manual.