Run-Time Subroutine: Returns the floating-point processor control word. This routine is only available on ia32 processors.
Module: USE DFLIB
Syntax
The floating-point control word is a bit flag that controls various modes of the floating-point coprocessor. The DFLIB.F90 module file (in the \DF98\INCLUDE subdirectory) contains constants defined for the control word as follows:
| Parameter name | Hex value | Description |
|---|---|---|
| FPCW$MCW_IC | #1000 | Infinity control mask |
| FPCW$AFFINE | #1000 | Affine infinity |
| FPCW$PROJECTIVE | #0000 | Projective infinity |
| FPCW$MCW_PC | #0300 | Precision control mask |
| FPCW$64 | #0300 | 64-bit precision |
| FPCW$53 | #0200 | 53-bit precision |
| FPCW$24 | #0000 | 24-bit precision |
| FPCW$MCW_RC | #0C00 | Rounding control mask |
| FPCW$CHOP | #0C00 | Truncate |
| FPCW$UP | #0800 | Round up |
| FPCW$DOWN | #0400 | Round down |
| FPCW$NEAR | #0000 | Round to nearest |
| FPCW$MSW_EM | #003F | Exception mask |
| FPCW$INVALID | #0001 | Allow invalid numbers |
| FPCW$DENORMAL | #0002 | Allow denormals (very small numbers) |
| FPCW$ZERODIVIDE | #0004 | Allow divide by zero |
| FPCW$OVERFLOW | #0008 | Allow overflow |
| FPCW$UNDERFLOW | #0010 | Allow underflow |
| FPCW$INEXACT | #0020 | Allow inexact precision |
The defaults for the floating-point control word are 53-bit precision, round to nearest, and the denormal, underflow and inexact precision exceptions disabled. An exception is disabled if its flag is set to 1 and enabled if its flag is cleared to 0. Exceptions can be disabled by setting the flags to 1 with SETCONTROLFPQQ.
If an exception is disabled, it does not cause an interrupt when it occurs. Instead, floating-point processes generate an appropriate special value (NaN or signed infinity), but the program continues.
You can find out which exceptions (if any) occurred by calling GETSTATUSFPQQ. If errors on floating-point exceptions are enabled (by clearing the flags to 0 with SETCONTROLFPQQ), the operating system generates an interrupt when the exception occurs. By default, these interrupts cause run-time errors, but you can capture the interrupts with SIGNALQQ and branch to your own error-handling routines.
You can use GETCONTROLFPQQ to retrieve the current control word and SETCONTROLFPQQ to change the control word. Most users do not need to change the default settings. For a full discussion of the floating-point control word, exceptions, and error handling, see The Floating-Point Environment in the Programmer's Guide.
Compatibility
CONSOLE STANDARD GRAPHICS QUICKWIN GRAPHICS WINDOWS DLL LIB
See Also: SETCONTROLFPQQ, GETSTATUSFPQQ, SIGNALQQ, MATHERRQQ, CLEARSTATUSFPQQ
Example
USE DFLIB
INTEGER(2) control
CALL GETCONTROLFPQQ (control)
!if not rounding down
IF (IAND(control, FPCW$DOWN) .NE. FPCW$DOWN) THEN
control = IAND(control, NOT(FPCW$MCW_RC)) ! clear all
! rounding
control = IOR(control, FPCW$DOWN) ! set to
! round down
CALL SETCONTROLFPQQ(control)
END IF
END