ieee_handler(3M) — MATHEMATICAL LIBRARY

NAME

ieee_handler − IEEE exception trap handler function

SYNOPSIS

/usr/ucb/cc [ flag. . . ] file . . .

#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 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

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