SIGFPE

SIGFPE

General Computational Error

Default handling
Ignoring the signal
Information returned by siginfo
Notes on defining a handler
USS Considerations

The SIGFPE signal is raised when a computational error occurs. These errors include floating-point overflow, floating-point underflow, and either integer- or floating-point division by 0. Note that integer overflow never causes a signal; when integer overflow occurs, the result is reduced to 32 bits by discarding the most significant bits and is then interpreted as a signed integer.

Default handling

The default handling for SIGFPE is to raise a more specific signal for the SIGFPOFL , SIGFPUFL , SIGFPDIV , or SIGIDIV conditions. Handling of the more specific signal depends on whether a handler has been defined for it. Refer to the descriptions of each of these signals for more details.

Ignoring the signal

If your program ignores SIGFPE , the result of the computation that raises SIGFPE is undefined, unless the computation causes an underflow. For underflows, the result is set to 0.

Information returned by siginfo

If you call siginfo after a SIGFPE signal occurs, siginfo returns a pointer to a structure of type FPE_t . This structure is defined as:

typedef struct {
   int int_code;       /* interrupt code                         */
   union {
      int *intv;       /* result for integer expression          */
      double *doublev; /* result for double expression           */
      } result;
   char *EPIE;         /* pointer to hardware program check info */
   double *fpregs;     /* floating-point register contents       */
   } FPE_t;

The int_code field contains the number of the more specific signal associated with the SIGFPOFL , SIGFPUFL , SIGFPDIV , or SIGIDIV conditions. The result field is a pointer to the result of the computation that raises the signal. If you want to continue processing, you can change the value that result points to.

The EPIE field is a pointer to a control block containing hardware information available at the time the signal occurs. (This information includes program status word and registers.) For information on the EPIE format, see IBM publication MVS/XA Supervisor Services and Macro Instructions. (Although an EPIE is provided only by the XA versions of the MVS and CMS operating systems, one is created by the run-time library for all MVS and CMS systems.)

The fpregs field is a pointer to an array of doubles that contains the contents of the floating-point registers at the time of the signal and stored in the order 0, 2, 4, 6.

Notes on defining a handler

If you define a handler for SIGFPE , you can determine what type of error caused the signal by testing the int_code field of the information returned by siginfo . You can also use this information to reset the result of the computation by changing the value that result points to. Refer to the example in the description of the siginfo function for an illustration of this technique.

USS Considerations

When SIGFPE is managed by USS, the default action for SIGFPE is abnormal process termination, and SIGFPE is never converted into another signal. If you want to handle one or more of the SIGFPDIV , SIGFPOFL , SIGFPUFL , or SIGIDIV signals specific to SAS/C, you must define SIGFPE as a signal managed by SAS/C.

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