6.4.4 DCTIP

Description

DCTIP computes the Discrete Cosine Transform of a source vector in place.

Prototype

fractcomplex* DCTIP (int log2N, fractcomplex* srcCV, fractcomplex* cosFactors, fractcomplex* twidFactors);

Arguments


Parameters	Description
log2N	Base 2 logarithm of N (number of complex elements in source vector)
srcCV	Pointer to the source vector
cosFactors	Pointer to the cosine factors
twidFactors	Pointer to the twiddle factors

Return

Pointer to the base address of the destination sample.

Remarks

N must be an integer power of 2.

This function expects that the source vector has been zero padded to length 2N.

The srcCV vector must be allocated in the Y-Data space with address alignment to a modulo of N.

The results of computation are stored in the first N elements of the source vector.

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 cosine factors are needed.

Only the first N/2 twiddle factors are needed.

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

Output is scaled by the factor of N.

Source File

Function Profile


Program Words	PIC32A
	64


Cycle count	Transform Size	PIC32A
	Transform Size	Cycles if Twiddle Factors in X-mem	Cycles if Twiddle Factors in P-mem
	32	2,468	3,556
	64	5,350	7,926
	128	11,668	17,636
	256	25,478	39,062
	512	55,364	85,844
	1024	119,798	187,398
	2048	257,812	406,308

System resource usage