Developer Reference for Intel® Integrated Performance Primitives 2018
Computes the forward discrete cosine transform of a signal.
Case 1: Not-in-place operation
IppStatus ippsDCTFwd_32f(const Ipp32f* pSrc, Ipp32f* pDst, const IppsDCTFwdSpec_32f* pDCTSpec, Ipp8u* pBuffer);
IppStatus ippsDCTFwd_64f(const Ipp64f* pSrc, Ipp64f* pDst, const IppsDCTFwdSpec_64f* pDCTSpec, Ipp8u* pBuffer);
Case 2: In-place operation
IppStatus ippsDCTFwd_32f_I(Ipp32f* pSrcDst, const IppsDCTFwdSpec_32f* pDCTSpec, Ipp8u* pBuffer);
IppStatus ippsDCTFwd_64f_I(Ipp64f* pSrcDst, const IppsDCTFwdSpec_64f* pDCTSpec, Ipp8u* pBuffer);
ipps.h
Headers: ippcore.h, ippvm.h
Libraries: ippcore.lib, ippvm.lib
pDCTSpec |
Pointer to the forward 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 forward 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 ippsDCTFwdInit beforehand. The result in stored in the pDst (pSrcDst for in-place operations).
If len is a power of 2, the function 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 pSrc[n] and y(k) is pDst[k].
The forward 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 ippsDCTFwdGetSize.
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 if the specification identifier pDCTSpec is incorrect. |
ippStsMemAllocErr |
Indicates an error if memory allocation fails. |