6.4.11 IFFTRealIP

Description

IFFTRealIP computes, in place, the inverse Fast Fourier Transform of a source complex vector, which was derived out of a real-vector using the FFTReal function. The algorithm to compute IFFT is based on the efficient computation of IFFT of a 2N point complex vector using the N point complex FFT with additional computations called split functions.

Prototype

fractional* IFFTRealIP (int log2N, fractcomplex* srcCV, fractcomplex* twidFactors);

Arguments

Return

Pointer to the base address of the real destination sample.

Remarks

N must be an integer power of 2.

The complex srcCV vector must be of size N/2 + 1, holding zero to N/2 elements.

The elements in the source complex vector are expected in a natural order, and the resultant vector, likewise, returned in a natural order. The resulting transform is a real vector of size N stored in the same location as that of the source complex vector.

This function operates in-place. srcV must be a complex vector with N/2 + 1 elements. The resultant vector will be a real-vector of size N stored in same location as that of complex srcCV vector.

The dstCV vector must be allocated at a modulo alignment of N in y-memory space.

To avoid saturation (overflow) during computation, the values of the source vector should be in the range [-0.5, 0.5].

Only the first N/2 twiddle factors are needed.

This function internally utilizes the BitReversal function and parts of the FFTReal function.

The twiddle factors must be initialized with conjFlag set to a value other than zero.

Output is scaled by the factor of N.

Source File

• irfft_aa.s

Function Profile

System resource usage

• W0…W7 - used, not restored
• W8…W9 - saved, used, restored
• ACCA/ACCB - used, not restored
• CORCON - saved, used, restored
• REPEAT instruction(s) usage – 1
• Plus resources used by the BitReversalComplex function.