d520395340d6942a16fa8ef4dd1cca921d8e2798
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32 * g723_40_encoder(), g723_40_decoder()
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.
40 * The deviation from the bit level specification (lookup tables),
41 * preserves the bit level performance specifications.
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.
50 #include "g72x_priv.h"
53 * Maps G.723_40 code word to ructeconstructed scale factor normalized log
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};
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};
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.
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};
77 static short qtab_723_40
[15] = {-122, -16, 68, 139, 198, 250, 298, 339,
78 378, 413, 445, 475, 502, 528, 553};
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.
87 int g723_40_encoder (int sl
, G72x_STATE
*state_ptr
)
89 short sei
, sezi
, se
, sez
; /* ACCUM */
93 short dqsez
; /* ADDC */
96 /* linearize input sample to 14-bit PCM */
97 sl
>>= 2; /* sl of 14-bit dynamic range */
99 sezi
= predictor_zero(state_ptr
);
101 sei
= sezi
+ predictor_pole(state_ptr
);
102 se
= sei
>> 1; /* se = estimated signal */
104 d
= sl
- se
; /* d = estimation difference */
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 */
110 dq
= reconstruct(i
& 0x10, _dqlntab
[i
], y
); /* quantized diff */
112 sr
= (dq
< 0) ? se
- (dq
& 0x7FFF) : se
+ dq
; /* reconstructed signal */
114 dqsez
= sr
+ sez
- se
; /* dqsez = pole prediction diff. */
116 update(5, y
, _witab
[i
], _fitab
[i
], dq
, sr
, dqsez
, state_ptr
);
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.
128 int g723_40_decoder (int i
, G72x_STATE
*state_ptr
)
130 short sezi
, sei
, sez
, se
; /* ACCUM */
136 i
&= 0x1f; /* mask to get proper bits */
137 sezi
= predictor_zero(state_ptr
);
139 sei
= sezi
+ predictor_pole(state_ptr
);
140 se
= sei
>> 1; /* se = estimated signal */
142 y
= step_size(state_ptr
); /* adaptive quantizer step size */
143 dq
= reconstruct(i
& 0x10, _dqlntab
[i
], y
); /* estimation diff. */
145 sr
= (dq
< 0) ? (se
- (dq
& 0x7FFF)) : (se
+ dq
); /* reconst. signal */
147 dqsez
= sr
- se
+ sez
; /* pole prediction diff. */
149 update(5, y
, _witab
[i
], _fitab
[i
], dq
, sr
, dqsez
, state_ptr
);
151 return (sr
<< 2); /* sr was of 14-bit dynamic range */