getdct.3

来自「speech signal process tools」· 3 代码 · 共 57 行

.\" Copyright (c) 1987-1990 Entropic Speech, Inc.
.\" Copyright (c) 1997 Entropic Research Laboratory, Inc. All rights reserved.
.\" @(#)getdct.3	1.3 18 Apr 1997 ESI/ERL
.ds ]W (c) 1997 Entropic Research Laboratory, Inc.
.TH GET_DCT 3\-ESPSsp 18 Apr 1997
.SH NAME
get_dct \- Compute the forward or inverse discrete cosine transform of a
data sequence.
.SH SYNOPSIS
.ft B
get_dct ( data_in, data_out, size )
.br
float	data_in[], data_out[];
.br
int	size;
.SH DESCRIPTION
This routine computes the forward or inverse discrete cosine transform of a
sequence of data, using matrix multiplication. The input data are supplied
through the array
.B data_in.
The transform size is specified by
.B size.
Positive and negative values are used to indicate the forward and inverse
operations, respectively.
The output data are returned in the array
.B data_out.

The maximum transform size is 256. If the size is 0, or is greater than 256,
no operations are performed and the routine aborts with an assertion failure.
If the size is 1,
.B data_in[0]
is copied to
.B data_out[0].
.SH BUGS
None known.
.SH SEE ALSO
.nf
\fIget_fft\fP(3-ESPSsp).
.fi
.SH COMMENTS
This routine is intended for use with transform sizes which are not powers
of 2. In cases where the transform size is a power of 2, the well known
approach based on the double-size discrete Fourier transform is far more
efficient.

Because matrix multiplication is used, the computational time may be quite
significant for large transforms.
.SH FUTURE CHANGES
None anticipated.
.SH REFERENCES
[1] Elliott, D. F., and Rao, K. R.,
.I
FAST TRANSFORMS: Algorithms, Analyses, Applications,
Academic Press, Inc., Orlando, FL, 1982, p. 387.
.SH AUTHOR
Jim Elliott