On ia32 systems, the FPU status word includes bits that show the floating-point exception state of the processor. The status word parameters describe six exceptions: invalid result, denormalized result, zero divide, overflow, underflow and inexact precision. These are described in the section, Loss of Precision Errors: Rounding, Special Values, Underflow, and Overflow. When one of the bits is set to 1, it means a past floating-point operation produced that exception type. (Visual Fortran initially clears all status bits. It does not reset the status bits before performing additional floating-point operations after an exception occurs. The status bits accumulate.)
The following table shows the floating-point exception status parameters:
| Parameter Name | Value in Hex | Description |
|---|---|---|
| FPSW$MSW_EM | #003F | Status Mask (set all bits to 1) |
| FPSW$INVALID | #0001 | An invalid result occurred |
| FPSW$DENORMAL | #0002 | A denormal (very small number) occurred |
| FPSW$ZERODIVIDE | #0004 | A divide by zero occurred |
| FPSW$OVERFLOW | #0008 | An overflow occurred |
| FPSW$UNDERFLOW | #0010 | An underflow occurred |
| FPSW$INEXACT | #0020 | Inexact precision occurred |
You can find out which exceptions have occurred by retrieving the status word and comparing it to the exception parameters. For example:
USE DFLIB
INTEGER(2) status
CALL GETSTATUSFPQQ(status)
IF ((status .AND. FPSW$INEXACT) > 0) THEN
WRITE (*, *) "Inexact precision has occurred"
ELSE IF ((status .AND. FPSW$DENORMAL) > 0) THEN
WRITE (*, *) "Denormal occurred"
END IF
To clear the status word flags, call the CLEARSTATUSFPQQ (ia32 only) routine.