Intel® Fortran Compiler 17.0 Developer Guide and Reference
Portability Subroutine: Sets the value of the floating-point processor control word.
USE IFPORT
CALL SETCONTROLFPQQ (controlword)
controlword |
(Input) INTEGER(2). Floating-point processor control word. |
The floating-point control word specifies how various exception conditions are handled by the floating-point math coprocessor, sets the floating-point precision, and specifies the floating-point rounding mechanism used.
The control word can be any of the following constants (defined in IFPORT.F90):
Parameter name |
Hex value |
Description |
|---|---|---|
FPCW$MCW_IC |
Z'1000' |
Infinity control mask |
FPCW$AFFINE |
Z'1000' |
Affine infinity |
FPCW$PROJECTIVE |
Z'0000' |
Projective infinity |
FPCW$MCW_PC |
Z'0300' |
Precision control mask |
FPCW$64 |
Z'0300' |
64-bit precision |
FPCW$53 |
Z'0200' |
53-bit precision |
FPCW$24 |
Z'0000' |
24-bit precision |
FPCW$MCW_RC |
Z'0C00' |
Rounding control mask |
FPCW$CHOP |
Z'0C00' |
Truncate |
FPCW$UP |
Z'0800' |
Round up |
FPCW$DOWN |
Z'0400' |
Round down |
FPCW$NEAR |
Z'0000' |
Round to nearest |
FPCW$MCW_EM |
Z'003F' |
Exception mask |
FPCW$INVALID |
Z'0001' |
Allow invalid numbers |
FPCW$DENORMAL |
Z'0002' |
Allow denormals (very small numbers) |
FPCW$ZERODIVIDE |
Z'0004' |
Allow divide by zero |
FPCW$OVERFLOW |
Z'0008' |
Allow overflow |
FPCW$UNDERFLOW |
Z'0010' |
Allow underflow |
FPCW$INEXACT |
Z'0020' |
Allow inexact precision |
An exception is disabled if its control bit is set to 1. An exception is enabled if its control bit is cleared to 0.
Setting the floating-point precision and rounding mechanism can be useful if you are reusing old code that is sensitive to the floating-point precision standard used and you want to get the same results as on the old machine.
You can use GETCONTROLFPQQ to retrieve the current control word and SETCONTROLFPQQ to change the control word. Most users do not need to change the default settings. If you need to change the control word, always use SETCONTROLFPQQ to make sure that special routines handling floating-point stack exceptions and abnormal propagation work correctly.
The Intel® Fortran exception handler allows for software masking of invalid operations, but does not allow the math chip to mask them. If you choose to use the software masking, be aware that this can affect program performance if you compile code written for Intel Fortran with another compiler.
USE IFPORT
INTEGER(2) status, control, controlo
CALL GETCONTROLFPQQ(control)
WRITE (*, 9000) 'Control word: ', control
! Save old control word
controlo = control
! Clear all flags
control = control .AND. Z'0000'
! Set new control to round up
control = control .OR. FPCW$UP
CALL SETCONTROLFPQQ(control)
CALL GETCONTROLFPQQ(control)
WRITE (*, 9000) 'Control word: ', control
9000 FORMAT (1X, A, Z4)
END