interpretor/lib/src/libsndfile-1.0.25/src/G72x/g723_40.c

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  26
  27 /*
  28  * g723_40.c
  29  *
  30  * Description:
  31  *
  32  * g723_40_encoder(), g723_40_decoder()
  33  *
  34  * These routines comprise an implementation of the CCITT G.723 40Kbps
  35  * ADPCM coding algorithm.  Essentially, this implementation is identical to
  36  * the bit level description except for a few deviations which
  37  * take advantage of workstation attributes, such as hardware 2's
  38  * complement arithmetic.
  39  *
  40  * The deviation from the bit level specification (lookup tables),
  41  * preserves the bit level performance specifications.
  42  *
  43  * As outlined in the G.723 Recommendation, the algorithm is broken
  44  * down into modules.  Each section of code below is preceded by
  45  * the name of the module which it is implementing.
  46  *
  47  */
  48
  49 #include "g72x.h"
  50 #include "g72x_priv.h"
  51
  52 /*
  53  * Maps G.723_40 code word to ructeconstructed scale factor normalized log
  54  * magnitude values.
  55  */
  56 static short    _dqlntab[32] = {-2048, -66, 28, 104, 169, 224, 274, 318,
  57                                 358, 395, 429, 459, 488, 514, 539, 566,
  58                                 566, 539, 514, 488, 459, 429, 395, 358,
  59                                 318, 274, 224, 169, 104, 28, -66, -2048};
  60
  61 /* Maps G.723_40 code word to log of scale factor multiplier. */
  62 static short    _witab[32] = {448, 448, 768, 1248, 1280, 1312, 1856, 3200,
  63                         4512, 5728, 7008, 8960, 11456, 14080, 16928, 22272,
  64                         22272, 16928, 14080, 11456, 8960, 7008, 5728, 4512,
  65                         3200, 1856, 1312, 1280, 1248, 768, 448, 448};
  66
  67 /*
  68  * Maps G.723_40 code words to a set of values whose long and short
  69  * term averages are computed and then compared to give an indication
  70  * how stationary (steady state) the signal is.
  71  */
  72 static short    _fitab[32] = {0, 0, 0, 0, 0, 0x200, 0x200, 0x200,
  73                         0x200, 0x200, 0x400, 0x600, 0x800, 0xA00, 0xC00, 0xC00,
  74                         0xC00, 0xC00, 0xA00, 0x800, 0x600, 0x400, 0x200, 0x200,
  75                         0x200, 0x200, 0x200, 0, 0, 0, 0, 0};
  76
  77 static short qtab_723_40[15] = {-122, -16, 68, 139, 198, 250, 298, 339,
  78                                 378, 413, 445, 475, 502, 528, 553};
  79
  80 /*
  81  * g723_40_encoder()
  82  *
  83  * Encodes a 16-bit linear PCM, A-law or u-law input sample and retuens
  84  * the resulting 5-bit CCITT G.723 40Kbps code.
  85  * Returns -1 if the input coding value is invalid.
  86  */
  87 int     g723_40_encoder (int sl, G72x_STATE *state_ptr)
  88 {
  89         short           sei, sezi, se, sez;     /* ACCUM */
  90         short           d;                      /* SUBTA */
  91         short           y;                      /* MIX */
  92         short           sr;                     /* ADDB */
  93         short           dqsez;                  /* ADDC */
  94         short           dq, i;
  95
  96         /* linearize input sample to 14-bit PCM */
  97         sl >>= 2;               /* sl of 14-bit dynamic range */
  98
  99         sezi = predictor_zero(state_ptr);
 100         sez = sezi >> 1;
 101         sei = sezi + predictor_pole(state_ptr);
 102         se = sei >> 1;                  /* se = estimated signal */
 103
 104         d = sl - se;                    /* d = estimation difference */
 105
 106         /* quantize prediction difference */
 107         y = step_size(state_ptr);       /* adaptive quantizer step size */
 108         i = quantize(d, y, qtab_723_40, 15);    /* i = ADPCM code */
 109
 110         dq = reconstruct(i & 0x10, _dqlntab[i], y);     /* quantized diff */
 111
 112         sr = (dq < 0) ? se - (dq & 0x7FFF) : se + dq; /* reconstructed signal */
 113
 114         dqsez = sr + sez - se;          /* dqsez = pole prediction diff. */
 115
 116         update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 117
 118         return (i);
 119 }
 120
 121 /*
 122  * g723_40_decoder()
 123  *
 124  * Decodes a 5-bit CCITT G.723 40Kbps code and returns
 125  * the resulting 16-bit linear PCM, A-law or u-law sample value.
 126  * -1 is returned if the output coding is unknown.
 127  */
 128 int     g723_40_decoder (int i, G72x_STATE *state_ptr)
 129 {
 130         short           sezi, sei, sez, se;     /* ACCUM */
 131         short           y ;                     /* MIX */
 132         short           sr;                     /* ADDB */
 133         short           dq;
 134         short           dqsez;
 135
 136         i &= 0x1f;                      /* mask to get proper bits */
 137         sezi = predictor_zero(state_ptr);
 138         sez = sezi >> 1;
 139         sei = sezi + predictor_pole(state_ptr);
 140         se = sei >> 1;                  /* se = estimated signal */
 141
 142         y = step_size(state_ptr);       /* adaptive quantizer step size */
 143         dq = reconstruct(i & 0x10, _dqlntab[i], y);     /* estimation diff. */
 144
 145         sr = (dq < 0) ? (se - (dq & 0x7FFF)) : (se + dq); /* reconst. signal */
 146
 147         dqsez = sr - se + sez;          /* pole prediction diff. */
 148
 149         update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 150
 151         return (sr << 2);       /* sr was of 14-bit dynamic range */
 152 }
 153