sigfpe(3C)

NAME

     sigfpe - signal handling for specific SIGFPE codes

SYNOPSIS

     #include <floatingpoint.h>
     #include <siginfo.h>

     sigfpe_handler_type      sigfpe(sigfpe_code_type       code,
     sigfpe_handler_type hdl);

DESCRIPTION

     This function allows signal handling  to  be  specified  for
     particular  SIGFPE  codes.  A call to sigfpe() defines a new
     handler hdl for a particular SIGFPE code and returns the old
     handler  as  the  value  of the function sigfpe().  Normally
     handlers are specified as pointers to functions; the special
     cases  SIGFPE_IGNORE, SIGFPE_ABORT, and SIGFPE_DEFAULT allow
     ignoring, dumping core using abort(3C), or default  handling
     respectively.   Default  handling  is  to  dump  core  using
     abort(3C).

     code is usually  one  of  the  five  IEEE754-related  SIGFPE
     codes:

     FPE_FLTRES   fp_inexact - floating-point inexact result
     FPE_FLTDIV   fp_division - floating-point division by zero
     FPE_FLTUND   fp_underflow - floating-point underflow
     FPE_FLTOVF   fp_overflow - floating-point overflow
     FPE_FLTINV   fp_invalid - floating-point invalid operation

     Three steps are required  to  intercept  an  IEEE754-related
     SIGFPE code with sigfpe():

     1. Set up a handler with sigfpe().

     2. Enable the relevant IEEE754 trapping  capability  in  the
        hardware,  perhaps  by  using  assembly-language instruc-
        tions.

     3. Perform a floating-point  operation  that  generates  the
        intended IEEE754 exception.

     sigfpe() never changes  floating-point  hardware  mode  bits
     affecting  IEEE754 trapping.  No IEEE754-related SIGFPE sig-
     nals will be generated unless those hardware mode  bits  are
     enabled.

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

EXAMPLES

     Example 1: Example Of A User-Specified Signal Handler

     A user-specified signal handler might look like this:

     #include <floatingpoint.h>
     #include <siginfo.h>
     #include <ucontext.h>
     /*
     * The sample_handler prints out a message then commits suicide.
     */
     void
     sample_handler(int sig, siginfo_t *sip, ucontext_t *uap) {
          char *label;
             switch (sip->si_code) {
          case FPE_FLTINV: label = "invalid operand"; break;
          case FPE_FLTRES: label = "inexact"; break;
          case FPE_FLTDIV: label = "division-by-zero"; break;
          case FPE_FLTUND: label = "underflow"; break;
          case FPE_FLTOVF: label = "overflow"; break;
          default: label = "???"; break;
          }
          fprintf(stderr, "FP exception %s (0x%x) occurred at address %p.\n",
                             label, sip->si_code, (void *) sip->si_addr);
          abort();
     }

     and it might be set up like this:

     #include <floatingpoint.h>
     #include <siginfo.h>
     #include <ucontext.h>
     extern void sample_handler(int, siginfo_t *, ucontext_t *);
     main(void) {
           sigfpe_handler_type hdl, old_handler1, old_handler2;
     /*
      * save current fp_overflow and fp_invalid handlers; set the new
     * fp_overflow handler to sample_handler() and set the new
     * fp_invalid handler to SIGFPE_ABORT (abort on invalid)
     */
         hdl = (sigfpe_handler_type) sample_handler;
         old_handler1 = sigfpe(FPE_FLTOVF, hdl);
         old_handler2 = sigfpe(FPE_FLTINV, SIGFPE_ABORT);
         ...
     /*
      * restore old fp_overflow and fp_invalid handlers
      */
          sigfpe(FPE_FLTOVF, old_handler1);
          sigfpe(FPE_FLTINV, old_handler2);
     }

FILES

     /usr/include/floatingpoint.h

     /usr/include/siginfo.h

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | Safe                        |
    |_____________________________|_____________________________|

SEE ALSO

     sigaction(2),    abort(3C),    signal(3C),    attributes(5),
     floatingpoint(3HEAD)

DIAGNOSTICS

     sigfpe() returns BADSIG if code is not  zero  or  a  defined
     SIGFPE code.