DSP_autocor
[Correlation]

Collaboration diagram for DSP_autocor:

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Detailed Description

void	DSP_autocor (short *restrict r, const short *restrict x, int nx, int nr)

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Function Documentation

void DSP_autocor	(	short *restrict	r,
		const short *restrict	x,
		int	nx,
		int	nr
	)

This routine performs an autocorrelation of an input vector x. The length of the autocorrelation is nx samples. Since nr such autocorrelations are performed, input vector x needs to be of length nx + nr. This produces nr output results which are stored in an output array r.

The following diagram illustrates how the correlations are obtained.

Example for nr=8, nx=24:
0 nr nx+nr-1
|-------|----------------------| <- x[]
| |----------------------| -> r[0]
| |----------------------| -> r[1]
| |----------------------| -> r[2]
| |----------------------| -> r[3]
| |----------------------| -> r[4]
| |----------------------| -> r[5]
| |----------------------| -> r[6]

Note that x[0] is never used, but is required for padding to make x[nr] double-word aligned.

Parameters:

	r	= Output data array of shorts
	x	= Input data array of shorts
	nx	= Length of autocorrelation
	nr	= Number of lags

Algorithm:

DSP_autocor_cn.c is the natural C equivalent of the optimized intrinsic C code without restrictions note that the intrinsic C code is optimized and restrictions may apply.

Assumptions:

The first nr elements are assumed to be zero.
NX >= 8; NX % 8 == 0
NR >= 4; NR % 4 == 0
x[] must be double word alligned

Implementation notes:

Endian Support: The code supports both big and little endian modes.
Interruptibility: The code is interruptible.

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Copyright 2014, Texas Instruments Incorporated