SetCpuFeatures

Sets the processor-specific library code for the specified processor features.

Syntax

IppStatus ippcpSetCpuFeatures(Ipp64u cpuFeatures);

Include Files

ippcp.h

Parameters

cpuFeatures

Features to be supported by the library. Refer to ippcpdefs.h for ippCPUID_xx definition.

Description

This function sets the processor-specific code of the Intel® Cryptography Primitives Library according to the processor features specified in cpuFeatures. You can use the following predefined sets of features (the FM suffix below means feature mask):

#define PX_FM ( ippCPUID_MMX | ippCPUID_SSE | ippCPUID_SSE2 )
#define M7_FM ( PX_FM | ippCPUID_SSE3 )
#define U8_FM ( M7_FM | ippCPUID_SSSE3 )
#define N8_FM ( U8_FM | ippCPUID_MOVBE )
#define Y8_FM ( U8_FM | ippCPUID_SSE41 | ippCPUID_SSE42 | ippCPUID_AES | ippCPUID_CLMUL | ippCPUID_SHA )
#define E9_FM ( Y8_FM | ippCPUID_AVX | ippAVX_ENABLEDBYOS | ippCPUID_RDRAND | ippCPUID_F16C )
#define L9_FM ( E9_FM | ippCPUID_MOVBE | ippCPUID_AVX2 | ippCPUID_ADCOX | ippCPUID_RDSEED | ippCPUID_PREFETCHW )
#define K0_FM ( L9_FM | ippCPUID_AVX512F )

Note

Do not use any other Intel® Cryptography Primitives Library function while ippcpSetCpuFeatures is executing. Otherwise, your application behavior is undefined.

Note

To avoid initialization of internal structures for one Intel® architecture and then call of the processing function that is optimized for another architecture, do not use the ippcpSetCpuFeatures function in chains of Intel® Cryptography Primitives Library connected calls like <processing functionGetSize + <processing functionInit + <processing function>. Otherwise, Intel® Cryptography Primitives Library functionality behavior is undefined.

Intel® Cryptography Primitives Library supports two internal sets of CPU features:

  • Real CPU features: the features that are supported by the CPU at which the library is executed. These features are read-only and can be obtained with the ippcpGetCpuFeatures function.

  • Enabled features: the features that are enabled externally to Intel® Cryptography Primitives Library by the application. These features can be set with ippcpSetCpuFeatures.

The ippcpSetCpuFeatures function provides additional flexibility in measuring performance improvements reached by using specific CPU features. For example, the first call of any Intel® Cryptography Primitives Library function in an application running on the 4th Generation Intel® Core™ i7 processor with 64-bit OS installed dispatches the L9 code version optimized for Intel® Advanced Vector Extensions 2 (Intel® AVX2) with several other features like fast 16-bit floating point support, Intel® AES New Instructions (Intel® AES-NI), PCLMULQDQ new instructions support.

To check performance improvement for all Intel® Cryptography Primitives Library functionality reached by using Intel® AVX2, you can run a benchmark for the currently dispatched version of code and then compare performance with the Intel® Advanced Vector Extensions (Intel® AVX) version of code with Intel® AVX2 disabled. To disable Intel AVX2, call ippcpSetCpuFeatures(E9_FM). To enable Intel AVX2 back, call ippcpSetCpuFeatures( L9_FM ). Thus, you can use the ippcpSetCpuFeatures function to dispatch any version of Intel® Cryptography Primitives Library code and enable/disable specific CPU features. If you are not well familiar with the features of your CPU, use the auto-initialization mechanism for the default library behavior.

Product and Performance Information

Performance varies by use, configuration and other factors. Learn more at https://edc.intel.com/content/www/us/en/products/performance/benchmarks/overview/. Notice revision #20201201

Return Values

ippStsNoErr

Indicates that the required processor-specific code is successfully set.

ippStsCpuMismatch

Indicates that the specified processor features are not valid. Previously set code is used. If the requested feature is below the minimal supported by the px library - that is Intel® Streaming SIMD Extensions 2 (Intel® SSE2) for Intel® 64 architecture, px code is dispatched.

ippStsFeatureNotSupported

Indicates that the current CPU does not support at least one of the requested features. If the ippCPUID_NOCHECK bit of the cpuFeatures parameter is set to 1, these not supported features are enabled, otherwise - disabled.

ippStsUnknownFeature

Indicates that at least one of the requested features is unknown. It means that the feature is not defined in the ippdefs.h file. Further behavior of the library depends on known features passed to cpuFeatures. Unknown features are ignored.

ippStsFeaturesCombination

Indicates that the combination of features is not correct. For example, ippCPUID_AVX2 bit is set to 1 in cpuFeatures, but at least one of the ippCPUID_MMX, ippCPUID_SSE, …, ippCPUID_AVX bits is not set. All these missing bits, if supported by CPU, are set to 1. This means that if the library supports the Intel® AVX2 code, it also internally uses all known MMX™, Intel® SSE, and Intel® AVX extensions, which are below Intel® AVX2.