ieee_handler(3M-BSD)
MISC. REFERENCE MANUAL PAGE
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eee_handler(3M-BSD)



NAME
     ieeehandler - IEEE exception trap handler function

SYNOPSIS
     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 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 == SIGFPEDEFAULT  or
     SIGFPEIGNORE;  then  ieeehandler  will disable the trap on
     exception.  When hdl == SIGFPEABORT, 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 ieeehandler:

     1)   Set up a handler with ieeehandler.

     2)   Perform a floating-point operation that  generates  the
          intended    IEEE    exception.     Unlike    sigfpe(3),
          ieeehandler also adjusts floating-point hardware  mode
          bits  affecting  IEEE trapping.  For ``clear'', ``set''
          SIGFPEDEFAULT, or ``set'' SIGFPEIGNORE, 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
          ieeehandler(3M).  In a particular  program,  to  avoid
          confusion,  use  only one of these interfaces to handle
          SIGFPE signals.




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ieee_handler(3M-BSD)
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eee_handler(3M-BSD)



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).

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
          */
               ieeehandler("get","overflow",oldhandler1);
               ieeehandler("get","invalid", oldhandler2);
          /*
          * set new overflow handler to samplehandler and set new
          * invalid handler to SIGFPEABORT (abort on invalid)
          */
               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




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ieee_handler(3M-BSD)
MISC. REFERENCE MANUAL PAGE
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eee_handler(3M-BSD)



SEE ALSO
     floatingpoint(3),  ieeehandler(3),   sigfpe(3),   signal(3)
     sigvec(3),  signal(2),  abort(3C) in the Programmer's Refer-
     ence Manual.



















































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