On systems based on the IA-32 architecture, the FPU control word includes bits that control the FPU's precision, rounding mode, and whether exceptions generate signals if they occur. You can read the control word value with GETCONTROLFPQQ (IA-32 architecture only) to find out the current control settings, and you can change the control word with SETCONTROLFPQQ (IA-32 architecture only).
Note
The GETCONTROLFPQQ and SETCONTROLFPQQ routines only affect the x87 status register. They do not affect the MXCSR register (the control and status register for the SSE and SSE2 instructions).
Each bit in the floating-point control word corresponds to a mode of the floating-point math processor. The IFORT.F90 module file in the ...\INCLUDE folder contains the INTEGER(2) parameters defined for the control word, as shown in the following table:
Parameter Name |
Value in Hex |
Description |
|---|---|---|
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$MCW_EM |
#003F |
Exception mask |
FPCW$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 control word defaults are:
53-bit precision
Round to nearest (rounding mode)
The denormal, underflow, overflow, divide-by-zero, invalid, and inexact precision exceptions are disabled (do not generate an exception). To change exception handling, you can use the -fpe (Linux* and Mac OS* X) or the /fpe (Windows*) compiler option or the FOR_SET_FPE routine.