src/g721.c

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  25
  26 /*
  27  * g721.c
  28  *
  29  * Description:
  30  *
  31  * g721_encoder(), g721_decoder()
  32  *
  33  * These routines comprise an implementation of the CCITT G.721 ADPCM
  34  * coding algorithm.  Essentially, this implementation is identical to
  35  * the bit level description except for a few deviations which
  36  * take advantage of work station attributes, such as hardware 2's
  37  * complement arithmetic and large memory.  Specifically, certain time
  38  * consuming operations such as multiplications are replaced
  39  * with lookup tables and software 2's complement operations are
  40  * replaced with hardware 2's complement.
  41  *
  42  * The deviation from the bit level specification (lookup tables)
  43  * preserves the bit level performance specifications.
  44  *
  45  * As outlined in the G.721 Recommendation, the algorithm is broken
  46  * down into modules.  Each section of code below is preceded by
  47  * the name of the module which it is implementing.
  48  *
  49  */
  50
  51 #include "sox_i.h"
  52 #include "g72x.h"
  53 #include "g711.h"
  54
  55 static const 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 const 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 const 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 const 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 g721_encoder(int sl, int in_coding, struct g72x_state *state_ptr)
  81 {
  82         short           sezi, se, sez;          /* ACCUM */
  83         short           d;                      /* SUBTA */
  84         short           sr;                     /* ADDB */
  85         short           y;                      /* MIX */
  86         short           dqsez;                  /* ADDC */
  87         short           dq, i;
  88
  89         switch (in_coding) {    /* linearize input sample to 14-bit PCM */
  90         case AUDIO_ENCODING_ALAW:
  91                 sl = sox_alaw2linear16(sl) >> 2;
  92                 break;
  93         case AUDIO_ENCODING_ULAW:
  94                 sl = sox_ulaw2linear16(sl) >> 2;
  95                 break;
  96         case AUDIO_ENCODING_LINEAR:
  97                 sl >>= 2;                       /* 14-bit dynamic range */
  98                 break;
  99         default:
 100                 return (-1);
 101         }
 102
 103         sezi = predictor_zero(state_ptr);
 104         sez = sezi >> 1;
 105         se = (sezi + predictor_pole(state_ptr)) >> 1;   /* estimated signal */
 106
 107         d = sl - se;                            /* estimation difference */
 108
 109         /* quantize the prediction difference */
 110         y = step_size(state_ptr);               /* quantizer step size */
 111         i = quantize(d, y, qtab_721, 7);        /* i = ADPCM code */
 112
 113         dq = reconstruct(i & 8, _dqlntab[i], y);        /* quantized est diff */
 114
 115         sr = (dq < 0) ? se - (dq & 0x3FFF) : se + dq;   /* reconst. signal */
 116
 117         dqsez = sr + sez - se;                  /* pole prediction diff. */
 118
 119         update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 120
 121         return (i);
 122 }
 123
 124 /*
 125  * g721_decoder()
 126  *
 127  * Description:
 128  *
 129  * Decodes a 4-bit code of G.721 encoded data of i and
 130  * returns the resulting linear PCM, A-law or u-law value.
 131  * return -1 for unknown out_coding value.
 132  */
 133 int g721_decoder(int i, int out_coding, struct g72x_state *state_ptr)
 134 {
 135         short           sezi, sei, sez, se;     /* ACCUM */
 136         short           y;                      /* MIX */
 137         short           sr;                     /* ADDB */
 138         short           dq;
 139         short           dqsez;
 140
 141         i &= 0x0f;                      /* mask to get proper bits */
 142         sezi = predictor_zero(state_ptr);
 143         sez = sezi >> 1;
 144         sei = sezi + predictor_pole(state_ptr);
 145         se = sei >> 1;                  /* se = estimated signal */
 146
 147         y = step_size(state_ptr);       /* dynamic quantizer step size */
 148
 149         dq = reconstruct(i & 0x08, _dqlntab[i], y); /* quantized diff. */
 150
 151         sr = (dq < 0) ? (se - (dq & 0x3FFF)) : se + dq; /* reconst. signal */
 152
 153         dqsez = sr - se + sez;                  /* pole prediction diff. */
 154
 155         update(4, y, _witab[i] << 5, _fitab[i], dq, sr, dqsez, state_ptr);
 156
 157         switch (out_coding) {
 158         case AUDIO_ENCODING_ALAW:
 159                 return (tandem_adjust_alaw(sr, se, y, i, 8, qtab_721));
 160         case AUDIO_ENCODING_ULAW:
 161                 return (tandem_adjust_ulaw(sr, se, y, i, 8, qtab_721));
 162         case AUDIO_ENCODING_LINEAR:
 163                 return (sr << 2);       /* sr was 14-bit dynamic range */
 164         default:
 165                 return (-1);
 166         }
 167 }