g723_16.c

一个实用的aac编码器

/*
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 * for unrestricted use.  Users may copy or modify this source code without
 * charge.
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 * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING
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 * Sun source code is provided with no support and without any obligation on
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 * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE
 * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
 * OR ANY PART THEREOF.
 *
 * In no event will Sun Microsystems, Inc. be liable for any lost revenue
 * or profits or other special, indirect and consequential damages, even if
 * Sun has been advised of the possibility of such damages.
 *
 * Sun Microsystems, Inc.
 * 2550 Garcia Avenue
 * Mountain View, California  94043
 */
/* 16kbps version created, used 24kbps code and changing as little as possible.
 * G.726 specs are available from ITU's gopher or WWW site (http://www.itu.ch)
 * If any errors are found, please contact me at [e-mail]
 *      -Marc Randolph
 */

/*
 * g723_16.c
 *
 * Description:
 *
 * g723_16_encoder(), g723_16_decoder()
 *
 * These routines comprise an implementation of the CCITT G.726 16 Kbps
 * ADPCM coding algorithm.  Essentially, this implementation is identical to
 * the bit level description except for a few deviations which take advantage
 * of workstation attributes, such as hardware 2's complement arithmetic.
 *
 */

#include "g72x.h"
#include "private.h"

/*
 * Maps G.723_16 code word to reconstructed scale factor normalized log
 * magnitude values.  Comes from Table 11/G.726
 */
static short   _dqlntab[4] = { 116, 365, 365, 116}; 

/* Maps G.723_16 code word to log of scale factor multiplier.
 *
 * _witab[4] is actually {-22 , 439, 439, -22}, but FILTD wants it
 * as WI << 5  (multiplied by 32), so we'll do that here 
 */
static short   _witab[4] = {-704, 14048, 14048, -704};

/*
 * Maps G.723_16 code words to a set of values whose long and short
 * term averages are computed and then compared to give an indication
 * how stationary (steady state) the signal is.
 */

/* Comes from FUNCTF */
static short   _fitab[4] = {0, 0xE00, 0xE00, 0};

/* Comes from quantizer decision level tables (Table 7/G.726)
 */
static short qtab_723_16[1] = {261};


/*
 * g723_16_encoder()
 *
 * Encodes a linear PCM, A-law or u-law input sample and returns its 2-bit code.
 * Returns -1 if invalid input coding value.
 */
int
g723_16_encoder(
       int             sl,
       G72x_STATE *state_ptr)
{
       short           sei, sezi, se, sez;     /* ACCUM */
       short           d;                      /* SUBTA */
       short           y;                      /* MIX */
       short           sr;                     /* ADDB */
       short           dqsez;                  /* ADDC */
       short           dq, i;

		/* linearize input sample to 14-bit PCM */
		sl >>= 2;               /* sl of 14-bit dynamic range */

       sezi = predictor_zero(state_ptr);
       sez = sezi >> 1;
       sei = sezi + predictor_pole(state_ptr);
       se = sei >> 1;                  /* se = estimated signal */

       d = sl - se;                    /* d = estimation diff. */

       /* quantize prediction difference d */
       y = step_size(state_ptr);       /* quantizer step size */
       i = quantize(d, y, qtab_723_16, 1);  /* i = ADPCM code */

             /* Since quantize() only produces a three level output
              * (1, 2, or 3), we must create the fourth one on our own
              */
       if (i == 3)                          /* i code for the zero region */
         if ((d & 0x8000) == 0)             /* If d > 0, i=3 isn't right... */
           i = 0;
           
       dq = reconstruct(i & 2, _dqlntab[i], y); /* quantized diff. */

       sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */

       dqsez = sr + sez - se;          /* pole prediction diff. */

       update(2, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

       return (i);
}

/*
 * g723_16_decoder()
 *
 * Decodes a 2-bit CCITT G.723_16 ADPCM code and returns
 * the resulting 16-bit linear PCM, A-law or u-law sample value.
 * -1 is returned if the output coding is unknown.
 */
int
g723_16_decoder(
       int             i,
       G72x_STATE *state_ptr)
{
       short           sezi, sei, sez, se;     /* ACCUM */
       short           y;                      /* MIX */
       short           sr;                     /* ADDB */
       short           dq;
       short           dqsez;

       i &= 0x03;                      /* mask to get proper bits */
       sezi = predictor_zero(state_ptr);
       sez = sezi >> 1;
       sei = sezi + predictor_pole(state_ptr);
       se = sei >> 1;                  /* se = estimated signal */

       y = step_size(state_ptr);       /* adaptive quantizer step size */
       dq = reconstruct(i & 0x02, _dqlntab[i], y); /* unquantize pred diff */

       sr = (dq < 0) ? (se - (dq & 0x3FFF)) : (se + dq); /* reconst. signal */

       dqsez = sr - se + sez;                  /* pole prediction diff. */

       update(2, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);

		/* sr was of 14-bit dynamic range */
		return (sr << 2);       
}