ftz, Qftz

Flushes denormal results to zero.

IDE Equivalent

None

Architectures

IntelŪ ItaniumŪ architecture

Syntax

Linux: -ftz
-no-ftz
Mac OS: None
Windows:  /Qftz
/Qftz-

Arguments

None

Default

OFF The compiler lets results gradually underflow.

Description

This option flushes denormal results to zero when the application is in the gradual underflow mode. It may improve performance if the denormal values are not critical to your application's behavior.  

This option only has an effect when the main program is being compiled. It sets the FTZ mode for the process. The initial thread and any threads subsequently created by that process will operate in FTZ mode.

On ItaniumŪ-based systems, optimization option O3 sets -ftz (Linux) or /Qftz (Windows). Optimization option O2 sets the -no-ftz (Linux) or /Qftz- (Windows) option.

If this option produces undesirable results of the numerical behavior of your program, you can turn the FTZ mode off by using -no-ftz or /Qftz- in the command line while still benefiting from the O3 optimizations.

Note

When SSE instructions are used on IA-32 systems, options -no-ftz and /Qftz- are ignored. However, you can enable gradual underflow with code in the main program that clears the FTZ and DAZ bits in the MXCSR. Be aware that denormal processing can significantly slow down computation.

Alternate Options

None