DFTInv_CToC

Syntax

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 complex values.
pDst	Pointer to the output array containing complex values.
pSrcRe	Pointer to the input array containing real parts of the signal.
pSrcIm	Pointer to the input array containing imaginary parts of the signal.
pDstRe	Pointer to the output array containing real parts of the signal.
pDstIm	Pointer to the output array containing imaginary parts of the signal.
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 functions ippsDFTInv_CToC and ippgDFTInv_CToC are declared in the ipps.h and ippgen.h files respectively. These functions compute the inverse DFT of a complex signal.

Case 1 and Case 2. The function flavors ippsDFTInv_CToC compute the inverse DFT according to the pDFTSpec specification parameters: the transform len, the normalization flag, and the specific code hint.

The functions using the complex data type, for example with 32fc suffixes, process the input complex array pSrc and store the result in pDst.

The functions using the real data type and processing complex signals represented by separate real pSrcRe and imaginary pSrcIm parts, for example with 32f suffixes, store the result separately in pDstRe and pDstIm, respectively.

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 ippsDFTGet BufSize_C 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 3. The function flavors ippgDFTInv_CToC and ippgDFTInv_CToC_<len> compute the forward 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_CToC_24_32fc performs the inverse DFT with the length 24. 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].

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.