interpreter/lib/src/libsndfile-1.0.25/src/G72x/g721.c

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  26
  27 /*
  28  * g721.c
  29  *
  30  * Description:
  31  *
  32  * g721_encoder(), g721_decoder()
  33  *
  34  * These routines comprise an implementation of the CCITT G.721 ADPCM
  35  * coding algorithm.  Essentially, this implementation is identical to
  36  * the bit level description except for a few deviations which
  37  * take advantage of work station attributes, such as hardware 2's
  38  * complement arithmetic and large memory.  Specifically, certain time
  39  * consuming operations such as multiplications are replaced
  40  * with lookup tables and software 2's complement operations are
  41  * replaced with hardware 2's complement.
  42  *
  43  * The deviation from the bit level specification (lookup tables)
  44  * preserves the bit level performance specifications.
  45  *
  46  * As outlined in the G.721 Recommendation, the algorithm is broken
  47  * down into modules.  Each section of code below is preceded by
  48  * the name of the module which it is implementing.
  49  *
  50  */
  51
  52 #include "g72x.h"
  53 #include "g72x_priv.h"
  54
  55 static short qtab_721[7] = {-124, 80, 178, 246, 300, 349, 400};
  56 /*
  57  * Maps G.721 code word to reconstructed scale factor normalized log
  58  * magnitude values.
  59  */
  60 static short    _dqlntab[16] = {-2048, 4, 135, 213, 273, 323, 373, 425,
  61                                 425, 373, 323, 273, 213, 135, 4, -2048};
  62
  63 /* Maps G.721 code word to log of scale factor multiplier. */
  64 static short    _witab[16] = {-12, 18, 41, 64, 112, 198, 355, 1122,
  65                                 1122, 355, 198, 112, 64, 41, 18, -12};
  66 /*
  67  * Maps G.721 code words to a set of values whose long and short
  68  * term averages are computed and then compared to give an indication
  69  * how stationary (steady state) the signal is.
  70  */
  71 static short    _fitab[16] = {0, 0, 0, 0x200, 0x200, 0x200, 0x600, 0xE00,
  72                                 0xE00, 0x600, 0x200, 0x200, 0x200, 0, 0, 0};
  73
  74 /*
  75  * g721_encoder()
  76  *
  77  * Encodes the input vale of linear PCM, A-law or u-law data sl and returns
  78  * the resulting code. -1 is returned for unknown input coding value.
  79  */
  80 int
  81 g721_encoder(
  82         int             sl,
  83         G72x_STATE *state_ptr)
  84 {
  85         short           sezi, se, sez;          /* ACCUM */
  86         short           d;                      /* SUBTA */
  87         short           sr;                     /* ADDB */
  88         short           y;                      /* MIX */
  89         short           dqsez;                  /* ADDC */
  90         short           dq, i;
  91
  92         /* linearize input sample to 14-bit PCM */
  93         sl >>= 2;                       /* 14-bit dynamic range */
  94
  95         sezi = predictor_zero(state_ptr);
  96         sez = sezi >> 1;
  97         se = (sezi + predictor_pole(state_ptr)) >> 1;   /* estimated signal */
  98
  99         d = sl - se;                            /* estimation difference */
 100
 101         /* quantize the prediction difference */
 102         y = step_size(state_ptr);               /* quantizer step size */
 103         i = quantize(d, y, qtab_721, 7);        /* i = ADPCM code */
 104
 105         dq = reconstruct(i & 8, _dqlntab[i], y);        /* quantized est diff */
 106
 107         sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq;   /* reconst. signal */
 108
 109         dqsez = sr + sez - se;                  /* pole prediction diff. */
 110
 111         update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 112
 113         return (i);
 114 }
 115
 116 /*
 117  * g721_decoder()
 118  *
 119  * Description:
 120  *
 121  * Decodes a 4-bit code of G.721 encoded data of i and
 122  * returns the resulting linear PCM, A-law or u-law value.
 123  * return -1 for unknown out_coding value.
 124  */
 125 int
 126 g721_decoder(
 127         int             i,
 128         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 &= 0x0f;                      /* 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);       /* dynamic quantizer step size */
 143
 144         dq = reconstruct(i & 0x08, _dqlntab[i], y); /* quantized diff. */
 145
 146         sr = (dq < 0) ? (se - (dq & 0x3FFF)) : se + dq; /* reconst. signal */
 147
 148         dqsez = sr - se + sez;                  /* pole prediction diff. */
 149
 150         update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 151
 152         /* sr was 14-bit dynamic range */
 153         return (sr << 2);
 154 }
 155