vmlSetMode

Developer Reference for Intel® oneAPI Math Kernel Library for C

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ID 766684

Date 10/31/2024

Version

Public

Visible to Intel only — GUID: GUID-08DD1124-912F-4AB2-9E0E-90E988379D5E

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vmlSetMode

Sets a new mode for VM functions according to the mode parameter and stores the previous VM mode to oldmode.

Syntax

oldmode = vmlSetMode( mode );

Include Files

mkl.h

Input Parameters

Name	Type	Description
`mode`	const MKL_UINT	Specifies the VM mode to be set.

Output Parameters

Name	Type	Description
`oldmode`	unsigned int	Specifies the former VM mode.

Description

The vmlSetMode function sets a new mode for VM functions according to the mode parameter and stores the previous VM mode to oldmode. The mode change has a global effect on all the VM functions within a thread.

NOTE:

You can override the global mode setting and change the mode for a given VM function call by using a respective vm[s,d]<Func> variant of the function.

The mode parameter is designed to control accuracy, handling of denormalized numbers, and error handling. Table "Values of the mode Parameter" lists values of the mode parameter. You can obtain all other possible values of the mode parameter from the mode parameter values by a using bitwise OR ( | ) operation to combine one value for accuracy, one value for handling of denormalized numbers, and one value for error control options. The default value of the mode parameter is VML_HA | VML_FTZDAZ_CURRENT | VML_ERRMODE_DEFAULT.

The VML_FTZDAZ_ON mode is specifically designed to improve the performance of computations that involve denormalized numbers at the cost of reasonable accuracy loss. This mode changes the numeric behavior of the functions: denormalized input values are treated as zeros (DAZ = denormals-are-zero) and denormalized results are flushed to zero (FTZ = flush-to-zero). Accuracy loss may occur if input and/or output values are close to denormal range.

Values of the `mode` Parameter
Value of `mode`	Description
Accuracy Control
VML_HA	high accuracy versions of VM functions
VML_LA	low accuracy versions of VM functions
VML_EP	enhanced performance accuracy versions of VM functions
Denormalized Numbers Handling Control
VML_FTZDAZ_ON	Faster processing of denormalized inputs is enabled.
VML_FTZDAZ_OFF	Faster processing of denormalized inputs is disabled.
VML_FTZDAZ_CURRENT	Keep the current CPU settings for denormalized inputs.
Error Mode Control
VML_ERRMODE_IGNORE	On computation error, VM Error status is updated, but otherwise no action is set. Cannot be combined with other VML_ERRMODE settings.
VML_ERRMODE_NOERR	On computation error, VM Error status is not updated and no action is set. Cannot be combined with other VML_ERRMODE settings.
VML_ERRMODE_ERRNO	On error, the `errno` variable is set.
VML_ERRMODE_STDERR	On error, the error text information is written to `stderr`.
VML_ERRMODE_EXCEPT	On error, an exception is raised.
VML_ERRMODE_CALLBACK	On error, an additional error handler function is called.
VML_ERRMODE_DEFAULT	On error, the `errno` variable is set, an exception is raised, and an additional error handler function is called.

Product and Performance Information
Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex. Notice revision #20201201

Product and Performance Information

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.

Notice revision #20201201

Examples

The following example shows how to set low accuracy, fast processing for denormalized numbers and stderr error mode:

ClassicC:

vmlSetMode( VML_LA ); 
vmlSetMode( VML_LA | VML_FTZDAZ_ON | VML_ERRMODE_STDERR );

Parent topic: VM Service Functions

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Developer Reference for Intel® oneAPI Math Kernel Library for C

vmlSetMode

Syntax

Include Files

Input Parameters

Output Parameters

Description

Examples