apple.accelerate.enums

Class vDSP_DCT_Type

java.lang.Object

apple.accelerate.enums.vDSP_DCT_Type

public final class vDSP_DCT_Type
extends java.lang.Object

vDSP_DCT_CreateSetup is a DCT setup routine. It creates a setup object for use with the vDSP_DCT_Execute routine. See additional information above, at "How to use the Discrete Fourier Transform (DFT) and Discrete Cosine Transform (DCT) interfaces."

Parameters:

vDSP_DFT_Setup Previous

Previous is either zero or a previous DFT or DCT setup. If a previous setup is passed, the new setup will share data with the previous setup, if feasible (and with any other setups the previous setup shares with). If zero is passed, the routine will allocate and initialize new memory.

vDSP_Length Length

Length is the number of real elements to be transformed.

vDSP_DCT_Type Type

Type specifies which DCT variant to perform. At present, the supported DCT types are II and III (which are mutual inverses, up to scaling) and IV (which is its own inverse). These are specified with symbol names vDSP_DCT_II, vDSP_DCT_III, and vDSP_DCT_IV.

Return value:

Zero is returned if memory is unavailable or if there is no implementation for the requested case. Currently, the implemented cases are:

Length = f * 2**n, where f is 1, 3, 5, or 15 and 4 <= n.

Function:

When vDSP_DCT_Execute is called with a setup returned from this routine, it calculates:

If Type is vDSP_DCT_II:

For 0 <= k < N,

Or[k] = sum(Ir[j] * cos(k * (j+1/2) * pi / N, 0 <= j < N).

If Type is vDSP_DCT_III

For 0 <= k < N,

Or[k] = Ir[0]/2 + sum(Ir[j] * cos((k+1/2) * j * pi / N), 1 <= j < N).

If Type is vDSP_DCT_IV:

For 0 <= k < N,

Or[k] = sum(Ir[j] * cos((k+1/2) * (j+1/2) * pi / N, 0 <= j < N).

Where:

N is the length given in the setup,

h is the array of real numbers passed to vDSP_DCT_Execute in Input, and

H is the array of real numbers stored by vDSP_DCT_Execute in the array passed to it in Output.

Performance:

Performance is good when the array addresses (passed to vDSP_DFT_Execute) are 16-byte aligned. Other alignments are supported, but performance may be significantly worse in some cases, depending on the processor model or the transform length (because different algorithms are used for different forms of transform length).

In-Place Operation:

Output may equal Input (in the call the vDSP_DCT_Execute). Otherwise, no overlap is permitted between the two buffers.

The returned setup object may be used only with vDSP_DCT_Execute for the length given during setup.

Do not call this routine while any DFT or DCT routine sharing setup data might be executing.

Field Summary

Fields

Modifier and Type	Field and Description
static int	II
static int	III
static int	IV

Method Summary

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

II

public static final int II

See Also:

Constant Field Values

III

public static final int III

See Also:

Constant Field Values

IV

public static final int IV

See Also:

Constant Field Values