Some Intel IPP functions use special structures to store function-specific (context) information. For example, the

IppiFFTSpec

structure stores twiddle factors and bit reverse indexes needed in computing the fast Fourier transform.

Two different kinds of structures are used: structures that are not modified during function operation - they have the suffix

Spec

in their names, and structures that are modified during operation - they have the suffix

State

in their names.

These context-related structures are not defined in the public headers, and their fields are not accessible. It was done because the function context interpretation is processor dependent. Thus, you may only use context-related functions and may not create a function context as an automatic variable.