r_fft.c

完整的EVRC压缩解压缩算法源码,附带一个简单的例子程序。

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/*======================================================================*/
/*     Enhanced Variable Rate Codec - Bit-Exact C Specification         */
/*     Copyright (C) 1997-1998 Telecommunications Industry Association. */
/*     All rights reserved.                                             */
/*----------------------------------------------------------------------*/
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/*     development of North American Wideband CDMA Digital              */
/*     Cellular Telephony Standards is authorized by the TIA.           */
/*     The TIA does not authorize the use of this software for any      */
/*     other purpose.                                                   */
/*                                                                      */
/*     The availability of this software does not provide any license   */
/*     by implication, estoppel, or otherwise under any patent rights   */
/*     of TIA member companies or others covering any use of the        */
/*     contents herein.                                                 */
/*                                                                      */
/*     Any copies of this software or derivative works must include     */
/*     this and all other proprietary notices.                          */
/*======================================================================*/
/* r_fft.c */
/*****************************************************************
*
* This is an implementation of decimation-in-time FFT algorithm for
* real sequences.  The techniques used here can be found in several
* books, e.g., i) Proakis and Manolakis, "Digital Signal Processing",
* 2nd Edition, Chapter 9, and ii) W.H. Press et. al., "Numerical
* Recipes in C", 2nd Ediiton, Chapter 12.
*
* Input -  There are two inputs to this function:
*
*	1) An integer pointer to the input data array 
*	2) An integer value which should be set as +1 for FFT
*	   and some other value, e.g., -1 for IFFT
*
* Output - There is no return value.
*	The input data are replaced with transformed data.  If the
*	input is a real time domain sequence, it is replaced with
*	the complex FFT for positive frequencies.  The FFT value 
*	for DC and the foldover frequency are combined to form the
*	first complex number in the array.  The remaining complex
*	numbers correspond to increasing frequencies.  If the input
*	is a complex frequency domain sequence arranged	as above,
*	it is replaced with the corresponding time domain sequence. 
*
* Notes:
*
*	1) This function is designed to be a part of a noise supp-
*	   ression algorithm that requires 128-point FFT of real
*	   sequences.  This is achieved here through a 64-point
*	   complex FFT.  Consequently, the FFT size information is
*	   not transmitted explicitly.  However, some flexibility
*	   is provided in the function to change the size of the 
*	   FFT by specifying the size information through "define"
*	   statements.
*
*	2) The values of the complex sinusoids used in the FFT 
*	   algorithm are computed once (i.e., the first time the
*	   r_fft function is called) and stored in a table. To
*	   further speed up the algorithm, these values can be
*	   precomputed and stored in a ROM table in actual DSP
*	   based implementations.
*
*	3) In the c_fft function, the FFT values are divided by
*	   2 after each stage of computation thus dividing the
*	   final FFT values by 64.  No multiplying factor is used
*	   for the IFFT.  This is somewhat different from the usual
*	   definition of FFT where the factor 1/N, i.e., 1/64, is
*	   used for the IFFT and not the FFT.  No factor is used in
*	   the r_fft function.
*
*	4) Much of the code for the FFT and IFFT parts in r_fft
*	   and c_fft functions are similar and can be combined.
*	   They are, however, kept separate here to speed up the
*	   execution.
*
*****************************************************************/
#include "mathevrc.h"
#include "mathdp31.h"
#include "mathadv.h"

#define			SIZE			128
#define			SIZE_BY_TWO		64
#define			NUM_STAGE		6
#define			TRUE			1
#define			FALSE			0

static Shortword phs_tbl[] =
{

	32767, 0, 32729, -1608, 32610, -3212, 32413, -4808,
	32138, -6393, 31786, -7962, 31357, -9512, 30853, -11039,
	30274, -12540, 29622, -14010, 28899, -15447, 28106, -16846,
	27246, -18205, 26320, -19520, 25330, -20788, 24279, -22006,
	23170, -23170, 22006, -24279, 20788, -25330, 19520, -26320,
	18205, -27246, 16846, -28106, 15447, -28899, 14010, -29622,
	12540, -30274, 11039, -30853, 9512, -31357, 7962, -31786,
	6393, -32138, 4808, -32413, 3212, -32610, 1608, -32729,
	0, -32768, -1608, -32729, -3212, -32610, -4808, -32413,
	-6393, -32138, -7962, -31786, -9512, -31357, -11039, -30853,
	-12540, -30274, -14010, -29622, -15447, -28899, -16846, -28106,
	-18205, -27246, -19520, -26320, -20788, -25330, -22006, -24279,
	-23170, -23170, -24279, -22006, -25330, -20788, -26320, -19520,
	-27246, -18205, -28106, -16846, -28899, -15447, -29622, -14010,
	-30274, -12540, -30853, -11039, -31357, -9512, -31786, -7962,
	-32138, -6393, -32413, -4808, -32610, -3212, -32729, -1608

};

static Shortword ii_table[] =
{SIZE / 2, SIZE / 4, SIZE / 8, SIZE / 16, SIZE / 32, SIZE / 64};

/* FFT/IFFT function for complex sequences */

/*
 * The decimation-in-time complex FFT/IFFT is implemented below.
 * The input complex numbers are presented as real part followed by
 * imaginary part for each sample.  The counters are therefore
 * incremented by two to access the complex valued samples.
 */
void c_fft(Shortword * farray_ptr, Shortword isign)
{

	Shortword i, j, k, ii, jj, kk, ji, kj;
	Longword ftmp, ftmp_real, ftmp_imag;
	Shortword tmp, tmp1, tmp2;

/* Rearrange the input array in bit reversed order */
	for (i = 0, j = 0; i < SIZE - 2; i = i + 2)
	{
		if (j > i)
		{
			ftmp = *(farray_ptr + i);
			*(farray_ptr + i) = *(farray_ptr + j);