src/g723_40.c

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  25
  26 /*
  27  * g723_40.c
  28  *
  29  * Description:
  30  *
  31  * g723_40_encoder(), g723_40_decoder()
  32  *
  33  * These routines comprise an implementation of the CCITT G.723 40Kbps
  34  * ADPCM coding algorithm.  Essentially, this implementation is identical to
  35  * the bit level description except for a few deviations which
  36  * take advantage of workstation attributes, such as hardware 2's
  37  * complement arithmetic.
  38  *
  39  * The deviation from the bit level specification (lookup tables),
  40  * preserves the bit level performance specifications.
  41  *
  42  * As outlined in the G.723 Recommendation, the algorithm is broken
  43  * down into modules.  Each section of code below is preceded by
  44  * the name of the module which it is implementing.
  45  *
  46  */
  47 #include "sox_i.h"
  48 #include "g711.h"
  49 #include "g72x.h"
  50
  51 /*
  52  * Maps G.723_40 code word to ructeconstructed scale factor normalized log
  53  * magnitude values.
  54  */
  55 static const short      _dqlntab[32] = {-2048, -66, 28, 104, 169, 224, 274, 318,
  56                                 358, 395, 429, 459, 488, 514, 539, 566,
  57                                 566, 539, 514, 488, 459, 429, 395, 358,
  58                                 318, 274, 224, 169, 104, 28, -66, -2048};
  59
  60 /* Maps G.723_40 code word to log of scale factor multiplier. */
  61 static const short      _witab[32] = {448, 448, 768, 1248, 1280, 1312, 1856, 3200,
  62                         4512, 5728, 7008, 8960, 11456, 14080, 16928, 22272,
  63                         22272, 16928, 14080, 11456, 8960, 7008, 5728, 4512,
  64                         3200, 1856, 1312, 1280, 1248, 768, 448, 448};
  65
  66 /*
  67  * Maps G.723_40 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[32] = {0, 0, 0, 0, 0, 0x200, 0x200, 0x200,
  72                         0x200, 0x200, 0x400, 0x600, 0x800, 0xA00, 0xC00, 0xC00,
  73                         0xC00, 0xC00, 0xA00, 0x800, 0x600, 0x400, 0x200, 0x200,
  74                         0x200, 0x200, 0x200, 0, 0, 0, 0, 0};
  75
  76 static const short qtab_723_40[15] = {-122, -16, 68, 139, 198, 250, 298, 339,
  77                                 378, 413, 445, 475, 502, 528, 553};
  78
  79 /*
  80  * g723_40_encoder()
  81  *
  82  * Encodes a 16-bit linear PCM, A-law or u-law input sample and retuens
  83  * the resulting 5-bit CCITT G.723 40Kbps code.
  84  * Returns -1 if the input coding value is invalid.
  85  */
  86 int g723_40_encoder(int sl, int in_coding, struct g72x_state *state_ptr)
  87 {
  88         short           sei, sezi, se, sez;     /* ACCUM */
  89         short           d;                      /* SUBTA */
  90         short           y;                      /* MIX */
  91         short           sr;                     /* ADDB */
  92         short           dqsez;                  /* ADDC */
  93         short           dq, i;
  94
  95         switch (in_coding) {    /* linearize input sample to 14-bit PCM */
  96         case AUDIO_ENCODING_ALAW:
  97                 sl = sox_alaw2linear16(sl) >> 2;
  98                 break;
  99         case AUDIO_ENCODING_ULAW:
 100                 sl = sox_ulaw2linear16(sl) >> 2;
 101                 break;
 102         case AUDIO_ENCODING_LINEAR:
 103                 sl >>= 2;               /* sl of 14-bit dynamic range */
 104                 break;
 105         default:
 106                 return (-1);
 107         }
 108
 109         sezi = predictor_zero(state_ptr);
 110         sez = sezi >> 1;
 111         sei = sezi + predictor_pole(state_ptr);
 112         se = sei >> 1;                  /* se = estimated signal */
 113
 114         d = sl - se;                    /* d = estimation difference */
 115
 116         /* quantize prediction difference */
 117         y = step_size(state_ptr);       /* adaptive quantizer step size */
 118         i = quantize(d, y, qtab_723_40, 15);    /* i = ADPCM code */
 119
 120         dq = reconstruct(i & 0x10, _dqlntab[i], y);     /* quantized diff */
 121
 122         sr = (dq < 0) ? se - (dq & 0x7FFF) : se + dq; /* reconstructed signal */
 123
 124         dqsez = sr + sez - se;          /* dqsez = pole prediction diff. */
 125
 126         update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 127
 128         return (i);
 129 }
 130
 131 /*
 132  * g723_40_decoder()
 133  *
 134  * Decodes a 5-bit CCITT G.723 40Kbps code and returns
 135  * the resulting 16-bit linear PCM, A-law or u-law sample value.
 136  * -1 is returned if the output coding is unknown.
 137  */
 138 int g723_40_decoder(int i, int out_coding, struct g72x_state *state_ptr)
 139 {
 140         short           sezi, sei, sez, se;     /* ACCUM */
 141         short           y;                      /* MIX */
 142         short           sr;                     /* ADDB */
 143         short           dq;
 144         short           dqsez;
 145
 146         i &= 0x1f;                      /* mask to get proper bits */
 147         sezi = predictor_zero(state_ptr);
 148         sez = sezi >> 1;
 149         sei = sezi + predictor_pole(state_ptr);
 150         se = sei >> 1;                  /* se = estimated signal */
 151
 152         y = step_size(state_ptr);       /* adaptive quantizer step size */
 153         dq = reconstruct(i & 0x10, _dqlntab[i], y);     /* estimation diff. */
 154
 155         sr = (dq < 0) ? (se - (dq & 0x7FFF)) : (se + dq); /* reconst. signal */
 156
 157         dqsez = sr - se + sez;          /* pole prediction diff. */
 158
 159         update(5, y, _witab[i], _fitab[i], dq, sr, dqsez, state_ptr);
 160
 161         switch (out_coding) {
 162         case AUDIO_ENCODING_ALAW:
 163                 return (tandem_adjust_alaw(sr, se, y, i, 0x10, qtab_723_40));
 164         case AUDIO_ENCODING_ULAW:
 165                 return (tandem_adjust_ulaw(sr, se, y, i, 0x10, qtab_723_40));
 166         case AUDIO_ENCODING_LINEAR:
 167                 return (sr << 2);       /* sr was of 14-bit dynamic range */
 168         default:
 169                 return (-1);
 170         }
 171 }