libsndfile/src/G72x/g723_24.c

   1 /*
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   3  * for unrestricted use.  Users may copy or modify this source code without
   4  * charge.
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  12  * modification or enhancement.
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  15  * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE
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  17  *
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  19  * or profits or other special, indirect and consequential damages, even if
  20  * Sun has been advised of the possibility of such damages.
  21  *
  22  * Sun Microsystems, Inc.
  23  * 2550 Garcia Avenue
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  26
  27 /*
  28  * g723_24.c
  29  *
  30  * Description:
  31  *
  32  * g723_24_encoder(), g723_24_decoder()
  33  *
  34  * These routines comprise an implementation of the CCITT G.723 24 Kbps
  35  * ADPCM coding algorithm.  Essentially, this implementation is identical to
  36  * the bit level description except for a few deviations which take advantage
  37  * of workstation attributes, such as hardware 2's complement arithmetic.
  38  *
  39  */
  40
  41 #include "g72x.h"
  42 #include "g72x_priv.h"
  43
  44 /*
  45  * Maps G.723_24 code word to reconstructed scale factor normalized log
  46  * magnitude values.
  47  */
  48 static short    _dqlntab[8] = {-2048, 135, 273, 373, 373, 273, 135, -2048};
  49
  50 /* Maps G.723_24 code word to log of scale factor multiplier. */
  51 static short    _witab[8] = {-128, 960, 4384, 18624, 18624, 4384, 960, -128};
  52
  53 /*
  54  * Maps G.723_24 code words to a set of values whose long and short
  55  * term averages are computed and then compared to give an indication
  56  * how stationary (steady state) the signal is.
  57  */
  58 static short    _fitab[8] = {0, 0x200, 0x400, 0xE00, 0xE00, 0x400, 0x200, 0};
  59
  60 static short qtab_723_24[3] = {8, 218, 331};
  61
  62 /*
  63  * g723_24_encoder()
  64  *
  65  * Encodes a linear PCM, A-law or u-law input sample and returns its 3-bit code.
  66  * Returns -1 if invalid input coding value.
  67  */
  68 int
  69 g723_24_encoder(
  70         int             sl,
  71         G72x_STATE *state_ptr)
  72 {
  73         short           sei, sezi, se, sez;     /* ACCUM */
  74         short           d;                      /* SUBTA */
  75         short           y;                      /* MIX */
  76         short           sr;                     /* ADDB */
  77         short           dqsez;                  /* ADDC */
  78         short           dq, i;
  79
  80         /* linearize input sample to 14-bit PCM */
  81         sl >>= 2;               /* sl of 14-bit dynamic range */
  82
  83         sezi = predictor_zero(state_ptr);
  84         sez = sezi >> 1;
  85         sei = sezi + predictor_pole(state_ptr);
  86         se = sei >> 1;                  /* se = estimated signal */
  87
  88         d = sl - se;                    /* d = estimation diff. */
  89
  90         /* quantize prediction difference d */
  91         y = step_size(state_ptr);       /* quantizer step size */
  92         i = quantize(d, y, qtab_723_24, 3);     /* i = ADPCM code */
  93         dq = reconstruct(i & 4, _dqlntab[i], y); /* quantized diff. */
  94
  95         sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq; /* reconstructed signal */
  96
  97         dqsez = sr + sez - se;          /* pole prediction diff. */
  98
  99         update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 100
 101         return (i);
 102 }
 103
 104 /*
 105  * g723_24_decoder()
 106  *
 107  * Decodes a 3-bit CCITT G.723_24 ADPCM code and returns
 108  * the resulting 16-bit linear PCM, A-law or u-law sample value.
 109  * -1 is returned if the output coding is unknown.
 110  */
 111 int
 112 g723_24_decoder(
 113         int             i,
 114         G72x_STATE *state_ptr)
 115 {
 116         short           sezi, sei, sez, se;     /* ACCUM */
 117         short           y;                      /* MIX */
 118         short           sr;                     /* ADDB */
 119         short           dq;
 120         short           dqsez;
 121
 122         i &= 0x07;                      /* mask to get proper bits */
 123         sezi = predictor_zero(state_ptr);
 124         sez = sezi >> 1;
 125         sei = sezi + predictor_pole(state_ptr);
 126         se = sei >> 1;                  /* se = estimated signal */
 127
 128         y = step_size(state_ptr);       /* adaptive quantizer step size */
 129         dq = reconstruct(i & 0x04, _dqlntab[i], y); /* unquantize pred diff */
 130
 131         sr = (dq < 0) ? (se - (dq & 0x3FFF)) : (se + dq); /* reconst. signal */
 132
 133         dqsez = sr - se + sez;                  /* pole prediction diff. */
 134
 135         update(3, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 136
 137         return (sr << 2);       /* sr was of 14-bit dynamic range */
 138 }