Computes the inverse discrete Fourier transform of a real signal.
Syntax
Case 1: Input data in Pack format
IppStatus ippsDFTInv_PackToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, const IppsDFTSpec_R_32f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_PackToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, const IppsDFTSpec_R_64f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_PackToR_16s_Sfs(const Ipp16s* pSrc, Ipp16s* pDst, const IppsDFTSpec_R_16s* pDFTSpec, int scaleFactor, Ipp8u* pBuffer);
Case 2: Input data in Pack format, fixed length of DFT
IppStatus ippgDFTInv_PackToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, int len, int flag);
IppStatus ippgDFTInv_PackToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, int len, int flag);
IppStatus ippgDFTInv_PackToR_<len>_32f(const Ipp32f* pSrc, Ipp32f* pDst, int flag);
IppStatus ippgDFTInv_PackToR_<len>_64f(const Ipp64f* pSrc, Ipp64f* pDst, int flag);
supported value for <len>: integer in the range [2, 64].
Case 3: Input data in Perm format
IppStatus ippsDFTInv_PermToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, const IppsDFTSpec_R_32f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_PermToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, const IppsDFTSpec_R_64f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_PermToR_16s_Sfs(const Ipp16s* pSrc, Ipp16s* pDst, const IppsDFTSpec_R_16s* pDFTSpec, int scaleFactor, Ipp8u* pBuffer);
Case 4: Result in Perm format, fixed length of DFT
IppStatus ippgDFTInv_PermToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, int len, int flag);
IppStatus ippgDFTInv_PermToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, int len, int flag);
IppStatus ippgDFTInv_PermToR_<len>_32f(const Ipp32f* pSrc, Ipp32f* pDst, int flag);
IppStatus ippgDFTInv_PermToR_<len>_64f(const Ipp64f* pSrc, Ipp64f* pDst, int flag);
supported value for <len>: integer in the range [2, 64].
Case 5: Input data in CSS format
IppStatus ippsDFTInv_CCSToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, const IppsDFTSpec_R_32f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_CCSToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, const IppsDFTSpec_R_64f* pDFTSpec, Ipp8u* pBuffer);
IppStatus ippsDFTInv_CCSToR_16s_Sfs(const Ipp16s* pSrc, Ipp16s* pDst, const IppsDFTSpec_R_16s* pDFTSpec, int scaleFactor, Ipp8u* pBuffer);
Case 6: Result in CCS format with fixed length of DFT
IppStatus ippgDFTInv_CCSToR_32f(const Ipp32f* pSrc, Ipp32f* pDst, int len, int flag);
IppStatus ippgDFTInv_CCSToR_64f(const Ipp64f* pSrc, Ipp64f* pDst, int len, int flag);
IppStatus ippgDFTInv_CCSToR_<len>_32f(const Ipp32f* pSrc, Ipp32f* pDst, int flag);
IppStatus ippgDFTInv_CCSToR_<len>_64f(const Ipp64f* pSrc, Ipp64f* pDst, int flag);
supported value for <len>: integer in the range [2, 64].
Parameters
pDFTSpec |
Pointer to the DFT specification structure. |
pSrc |
Pointer to the input array containing packed complex values. |
pDst |
Pointer to the output array containing real values. |
pBuffer |
Pointer to the work buffer, can be NULL. |
scaleFactor |
Scale factor, refer to Integer Scaling. |
flag |
Specifies the result normalization method. The values for the flag argument are described in the section Flag and Hint Arguments. |
len |
Length of the DFT transform in range [2, 64]. |
Description
The ippsDFTInv and ippgDFTInv function is declared in the ipps.h and ippgen.h files respectively . These functions compute the inverse DFT of a real signal. The input data (that is in the frequency-domain) are represented in several possible packed formats: Pack, Perm, or CCS. Tables show how the input data can be represented in the packed formats.
Case 1, Case3, Case 5. These functions compute the inverse DFT according to the pDFTSpec specification parameters: the transform len, the normalization flag, and the specific code hint.
For integer data types the output result is scaled according to the scaleFactor value, thus the output signal range and precision are retained.
The function can 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 DFT. 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.
Required buffer size must be computed by the corresponding function ippsDFTGetBufSize_R prior to using DFT computation functions.
If the external buffer is not specified (pBuffer is set to NULL), then the function itself allocates the memory needed for operation.
Case 2, Case 4, Case 6. These functions compute the inverse DFT of the fixed length. They do not need the DFT specification structure. The length of transform can be specified by the parameter len, or by choosing the function flavor designed for the specific length of transform and containing its value in the function name, for example, the function flavor ippgDFTInv_CCSToR_63_32f performs the inverse DFT with length 63. Intel IPP support functions for the inverse DFT with the fixed length in the range [2, 64].
Caution
Data vectors for these functions must be aligned to an appropriate number of bytes that is determined by the SIMD width that is supported by the customer's platform - use ippMalloc function for such alignment.
To avoid listing all the similar prototypes of function flavors of this type, only templates are given here. In the template the length of DFT is denoted by the modifier <len> and can be varied in the range of integers [2, 64].
The normalization method of the result is specified by the parameter flag.
The inverse DFT functionality can be described as follows:
where k is the index of elements in the frequency domain, n is the index of elements in the time domain, N is the input signal len, and B is a multiplier defined by flag. Also, x(n) is pDst[n] and X(k) is pSrc[k].
ippsDFTInv_PackToR. This function computes the inverse DFT for input data in Pack format.
ippsDFTInv_PermToR. This function computes the inverse DFT for input data in Perm format.
ippsDFTInv_CCSToR. This function computes the inverse DFT for input data in CCS format.
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Optimization Notice |
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Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice. Notice revision #20110804 |
Return Values
ippStsNoErr |
Indicates no error. |
ippStsNullPtrErr |
Indicates an error when one of the specified pointers with exception of pBuffer is NULL. |
ippStsContextMatchErr |
Indicates an error when the specification identifier pDFTSpec is incorrect. |
ippStsMemAllocErr |
Indicates an error when no memory is allocated. |
ippStsFftFlagErr |
Indicates an error when the flag value is incorrect. |