Developer Reference for Intel® Integrated Performance Primitives 2018
Computes the inverse discrete cosine transform of a signal.
Case 1: Not-in-place operation
IppStatus ippsDCTInv_32f(const Ipp32f* pSrc, Ipp32f* pDst, const IppsDCTInvSpec_32f* pDCTSpec, Ipp8u* pBuffer);
IppStatus ippsDCTInv_64f(const Ipp64f* pSrc, Ipp64f* pDst, const IppsDCTInvSpec_64f* pDCTSpec, Ipp8u* pBuffer);
Case 2: In-place operation
IppStatus ippsDCTInv_32f_I(Ipp32f* pSrcDst, const IppsDCTInvSpec_32f* pDCTSpec, Ipp8u* pBuffer);
IppStatus ippsDCTInv_64f_I(Ipp64f* pSrcDst, const IppsDCTInvSpec_64f* pDCTSpec, Ipp8u* pBuffer);
ipps.h
Headers: ippcore.h, ippvm.h
Libraries: ippcore.lib, ippvm.lib
pDCTSpec |
Pointer to the inverse DCT specification structure. |
pSrc |
Pointer to the source vector. |
pDst |
Pointer to the destination vector. |
pSrcDst |
Pointer to the source and destination vector for in-place operations. |
pBuffer |
Pointer to the external work buffer. |
This function computes the inverse discrete cosine transform (DCT) of the source signal pSrc (pSrcDst for in-place operations) in accordance with the specification structure pDCTSpec that must be initialized by calling ippsDCTInvInit beforehand. The result in stored in the pDst (pSrcDst for in-place operations).
If len is a power of 2, the functions use an efficient algorithm that is significantly faster than the direct computation of DCT. For other values of len, these functions use the direct formulas given below; however, the symmetry of the cosine function is taken into account, which allows to perform about half of the multiplication operations in the formulas.
In the following definition of DCT, N = len,
x(n) is pDst[n] and y(k) is pSrc[k].
The inverse DCT is defined by the formula:
The function may be used with the external work buffer pBuffer to avoid memory allocation within the functions. Once the work buffer is allocated, it can be used for all following calls to the functions computing DCT. As internal allocation of memory is too expensive operation and depends on operating system and/or runtime libraries used - the use of an external buffer improves performance significantly, especially for the small size transforms.
The size of this buffer must be computed previously using ippsDCTInvGetSize.
If the external buffer is not specified (pBuffer is set to NULL), then the function itself allocates the memory needed for operation.
ippStsNoErr |
Indicates no error. |
ippStsNullPtrErr |
Indicates an error if one of the pDCTSpec, pSrc, pDst, pSrcDst pointers is NULL. |
ippStsContextMatchErr |
Indicates an error when the specification identifier pDCTSpec is incorrect. |
ippStsMemAllocErr |
Indicates an error if memory allocation fails. |