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e8482f24 GL |
1 | /* |
2 | * This source code is a product of Sun Microsystems, Inc. and is provided | |
3 | * for unrestricted use. Users may copy or modify this source code without | |
4 | * charge. | |
5 | * | |
6 | * SUN SOURCE CODE IS PROVIDED AS IS WITH NO WARRANTIES OF ANY KIND INCLUDING | |
7 | * THE WARRANTIES OF DESIGN, MERCHANTIBILITY AND FITNESS FOR A PARTICULAR | |
8 | * PURPOSE, OR ARISING FROM A COURSE OF DEALING, USAGE OR TRADE PRACTICE. | |
9 | * | |
10 | * Sun source code is provided with no support and without any obligation on | |
11 | * the part of Sun Microsystems, Inc. to assist in its use, correction, | |
12 | * modification or enhancement. | |
13 | * | |
14 | * SUN MICROSYSTEMS, INC. SHALL HAVE NO LIABILITY WITH RESPECT TO THE | |
15 | * INFRINGEMENT OF COPYRIGHTS, TRADE SECRETS OR ANY PATENTS BY THIS SOFTWARE | |
16 | * OR ANY PART THEREOF. | |
17 | * | |
18 | * In no event will Sun Microsystems, Inc. be liable for any lost revenue | |
19 | * or profits or other special, indirect and consequential damages, even if | |
20 | * Sun has been advised of the possibility of such damages. | |
21 | * | |
22 | * Sun Microsystems, Inc. | |
23 | * 2550 Garcia Avenue | |
24 | * Mountain View, California 94043 | |
25 | */ | |
26 | ||
27 | /* | |
28 | * g72x.c | |
29 | * | |
30 | * Common routines for G.721 and G.723 conversions. | |
31 | */ | |
32 | ||
92a19c2e | 33 | #include "wx/wxprec.h" |
e8482f24 GL |
34 | #include <stdlib.h> |
35 | #include "wx/mmedia/internal/g72x.h" | |
36 | ||
37 | static short power2[15] = {1, 2, 4, 8, 0x10, 0x20, 0x40, 0x80, | |
38 | 0x100, 0x200, 0x400, 0x800, 0x1000, 0x2000, 0x4000}; | |
39 | ||
40 | /* | |
41 | * quan() | |
42 | * | |
43 | * quantizes the input val against the table of size short integers. | |
44 | * It returns i if table[i - 1] <= val < table[i]. | |
45 | * | |
46 | * Using linear search for simple coding. | |
47 | */ | |
48 | static int | |
49 | quan( | |
50 | int val, | |
51 | short *table, | |
52 | int size) | |
53 | { | |
54 | int i; | |
55 | ||
56 | for (i = 0; i < size; i++) | |
57 | if (val < *table++) | |
58 | break; | |
59 | return (i); | |
60 | } | |
61 | ||
62 | static char quan2_tab[65536]; | |
63 | static short base2_tab[65536]; | |
64 | static int init_tabs_done = 0; | |
65 | ||
66 | inline char quan2 (unsigned short val) | |
67 | { | |
68 | return quan2_tab[val]; | |
69 | } | |
70 | ||
71 | inline short base2 (unsigned short val) | |
72 | { | |
73 | return base2_tab[val]; | |
74 | } | |
75 | ||
76 | static void init_quan2_tab (void) | |
77 | { | |
78 | long i; | |
79 | ||
80 | for (i = 0; i < 65536; i++) { | |
81 | quan2_tab[i] = quan (i, power2, 15); | |
82 | }; | |
83 | } | |
84 | ||
85 | static void init_base2_tab (void) | |
86 | { | |
87 | long i; | |
88 | short exp; | |
89 | ||
90 | for (i = 0; i < 65536; i++) { | |
91 | exp = quan2 (short (i)); | |
92 | base2_tab[i] = short ((exp << 6) + ((i << 6) >> exp)); | |
93 | }; | |
94 | } | |
95 | ||
96 | static void init_tabs (void) | |
97 | { | |
98 | if (init_tabs_done) return; | |
99 | ||
100 | init_quan2_tab(); | |
101 | init_base2_tab(); | |
102 | ||
103 | init_tabs_done = 1; | |
104 | } | |
105 | ||
106 | /* | |
107 | * fmult() | |
108 | * | |
109 | * returns the integer product of the 14-bit integer "an" and | |
110 | * "floating point" representation (4-bit exponent, 6-bit mantessa) "srn". | |
111 | */ | |
112 | static int | |
113 | fmult( | |
114 | int an, | |
115 | int srn) | |
116 | { | |
117 | short anmag, anexp, anmant; | |
118 | short wanexp, wanmant; | |
119 | short retval; | |
120 | ||
121 | anmag = (an > 0) ? an : ((-an) & 0x1FFF); | |
122 | anexp = quan2(anmag) - 6; | |
123 | anmant = (anmag == 0) ? 32 : | |
124 | (anexp >= 0) ? anmag >> anexp : anmag << -anexp; | |
125 | wanexp = anexp + ((srn >> 6) & 0xF) - 13; | |
126 | ||
127 | wanmant = (anmant * (srn & 077) + 0x30) >> 4; | |
128 | retval = (wanexp >= 0) ? ((wanmant << wanexp) & 0x7FFF) : | |
129 | (wanmant >> -wanexp); | |
130 | ||
131 | return (((an ^ srn) < 0) ? -retval : retval); | |
132 | } | |
133 | ||
134 | /* | |
135 | * g72x_init_state() | |
136 | * | |
137 | * This routine initializes and/or resets the g72x_state structure | |
138 | * pointed to by 'state_ptr'. | |
139 | * All the initial state values are specified in the CCITT G.721 document. | |
140 | */ | |
141 | void | |
142 | g72x_init_state( | |
143 | struct g72x_state *state_ptr) | |
144 | { | |
145 | int cnta; | |
146 | ||
147 | init_tabs (); | |
148 | ||
149 | state_ptr->yl = 34816; | |
150 | state_ptr->yu = 544; | |
151 | state_ptr->dms = 0; | |
152 | state_ptr->dml = 0; | |
153 | state_ptr->ap = 0; | |
154 | for (cnta = 0; cnta < 2; cnta++) { | |
155 | state_ptr->a[cnta] = 0; | |
156 | state_ptr->pk[cnta] = 0; | |
157 | state_ptr->sr[cnta] = 32; | |
158 | } | |
159 | for (cnta = 0; cnta < 6; cnta++) { | |
160 | state_ptr->b[cnta] = 0; | |
161 | state_ptr->dq[cnta] = 32; | |
162 | } | |
163 | state_ptr->td = 0; | |
164 | } | |
165 | ||
166 | /* | |
167 | * predictor_zero() | |
168 | * | |
169 | * computes the estimated signal from 6-zero predictor. | |
170 | * | |
171 | */ | |
172 | int | |
173 | predictor_zero( | |
174 | struct g72x_state *state_ptr) | |
175 | { | |
176 | int i; | |
177 | int sezi; | |
178 | ||
179 | sezi = fmult(state_ptr->b[0] >> 2, state_ptr->dq[0]); | |
180 | for (i = 1; i < 6; i++) /* ACCUM */ | |
181 | sezi += fmult(state_ptr->b[i] >> 2, state_ptr->dq[i]); | |
182 | return (sezi); | |
183 | } | |
184 | /* | |
185 | * predictor_pole() | |
186 | * | |
187 | * computes the estimated signal from 2-pole predictor. | |
188 | * | |
189 | */ | |
190 | int | |
191 | predictor_pole( | |
192 | struct g72x_state *state_ptr) | |
193 | { | |
194 | return (fmult(state_ptr->a[1] >> 2, state_ptr->sr[1]) + | |
195 | fmult(state_ptr->a[0] >> 2, state_ptr->sr[0])); | |
196 | } | |
197 | /* | |
198 | * step_size() | |
199 | * | |
200 | * computes the quantization step size of the adaptive quantizer. | |
201 | * | |
202 | */ | |
203 | int | |
204 | step_size( | |
205 | struct g72x_state *state_ptr) | |
206 | { | |
207 | int y; | |
208 | int dif; | |
209 | int al; | |
210 | ||
211 | if (state_ptr->ap >= 256) | |
212 | return (state_ptr->yu); | |
213 | else { | |
214 | y = state_ptr->yl >> 6; | |
215 | dif = state_ptr->yu - y; | |
216 | al = state_ptr->ap >> 2; | |
217 | if (dif > 0) | |
218 | y += (dif * al) >> 6; | |
219 | else if (dif < 0) | |
220 | y += (dif * al + 0x3F) >> 6; | |
221 | return (y); | |
222 | } | |
223 | } | |
224 | ||
225 | /* | |
226 | * quantize() | |
227 | * | |
228 | * Given a raw sample, 'd', of the difference signal and a | |
229 | * quantization step size scale factor, 'y', this routine returns the | |
230 | * ADPCM codeword to which that sample gets quantized. The step | |
231 | * size scale factor division operation is done in the log base 2 domain | |
232 | * as a subtraction. | |
233 | */ | |
234 | int | |
235 | quantize( | |
236 | int d, /* Raw difference signal sample */ | |
237 | int y, /* Step size multiplier */ | |
238 | short *table, /* quantization table */ | |
239 | int size) /* table size of short integers */ | |
240 | { | |
241 | short dqm; /* Magnitude of 'd' */ | |
242 | short exp; /* Integer part of base 2 log of 'd' */ | |
243 | short mant; /* Fractional part of base 2 log */ | |
244 | short dl; /* Log of magnitude of 'd' */ | |
245 | short dln; /* Step size scale factor normalized log */ | |
246 | int i; | |
247 | ||
248 | /* | |
249 | * LOG | |
250 | * | |
251 | * Compute base 2 log of 'd', and store in 'dl'. | |
252 | */ | |
253 | dqm = abs(d); | |
254 | exp = quan2(dqm >> 1); | |
255 | mant = ((dqm << 7) >> exp) & 0x7F; /* Fractional portion. */ | |
256 | dl = (exp << 7) + mant; | |
257 | ||
258 | /* | |
259 | * SUBTB | |
260 | * | |
261 | * "Divide" by step size multiplier. | |
262 | */ | |
263 | dln = dl - (y >> 2); | |
264 | ||
265 | /* | |
266 | * QUAN | |
267 | * | |
268 | * Obtain codword i for 'd'. | |
269 | */ | |
270 | i = quan(dln, table, size); | |
271 | if (d < 0) /* take 1's complement of i */ | |
272 | return ((size << 1) + 1 - i); | |
273 | else if (i == 0) /* take 1's complement of 0 */ | |
274 | return ((size << 1) + 1); /* new in 1988 */ | |
275 | else | |
276 | return (i); | |
277 | } | |
278 | /* | |
279 | * reconstruct() | |
280 | * | |
281 | * Returns reconstructed difference signal 'dq' obtained from | |
282 | * codeword 'i' and quantization step size scale factor 'y'. | |
283 | * Multiplication is performed in log base 2 domain as addition. | |
284 | */ | |
285 | int | |
286 | reconstruct( | |
287 | int sign, /* 0 for non-negative value */ | |
288 | int dqln, /* G.72x codeword */ | |
289 | int y) /* Step size multiplier */ | |
290 | { | |
291 | short dql; /* Log of 'dq' magnitude */ | |
292 | short dex; /* Integer part of log */ | |
293 | short dqt; | |
294 | short dq; /* Reconstructed difference signal sample */ | |
295 | ||
296 | dql = dqln + (y >> 2); /* ADDA */ | |
297 | ||
298 | if (dql < 0) { | |
299 | return ((sign) ? -0x8000 : 0); | |
300 | } else { /* ANTILOG */ | |
301 | dex = (dql >> 7) & 15; | |
302 | dqt = 128 + (dql & 127); | |
303 | dq = (dqt << 7) >> (14 - dex); | |
304 | return ((sign) ? (dq - 0x8000) : dq); | |
305 | } | |
306 | } | |
307 | ||
308 | ||
309 | /* | |
310 | * update() | |
311 | * | |
312 | * updates the state variables for each output code | |
313 | */ | |
314 | void | |
315 | update( | |
316 | int code_size, /* distinguish 723_40 with others */ | |
317 | int y, /* quantizer step size */ | |
318 | int wi, /* scale factor multiplier */ | |
319 | int fi, /* for long/short term energies */ | |
320 | int dq, /* quantized prediction difference */ | |
321 | int sr, /* reconstructed signal */ | |
322 | int dqsez, /* difference from 2-pole predictor */ | |
323 | struct g72x_state *state_ptr) /* coder state pointer */ | |
324 | { | |
325 | int cnt; | |
326 | short mag; /* Adaptive predictor, FLOAT A */ | |
327 | short a2p; /* LIMC */ | |
328 | short a1ul; /* UPA1 */ | |
329 | short pks1; /* UPA2 */ | |
330 | short fa1; | |
331 | char tr; /* tone/transition detector */ | |
332 | short ylint, thr2, dqthr; | |
333 | short ylfrac, thr1; | |
334 | short pk0; | |
335 | ||
336 | pk0 = (dqsez < 0) ? 1 : 0; /* needed in updating predictor poles */ | |
337 | ||
338 | mag = dq & 0x7FFF; /* prediction difference magnitude */ | |
339 | /* TRANS */ | |
340 | ylint = short (state_ptr->yl >> 15); /* exponent part of yl */ | |
341 | ylfrac = (state_ptr->yl >> 10) & 0x1F; /* fractional part of yl */ | |
342 | thr1 = (32 + ylfrac) << ylint; /* threshold */ | |
343 | thr2 = (ylint > 9) ? 31 << 10 : thr1; /* limit thr2 to 31 << 10 */ | |
344 | dqthr = (thr2 + (thr2 >> 1)) >> 1; /* dqthr = 0.75 * thr2 */ | |
345 | if (state_ptr->td == 0) /* signal supposed voice */ | |
346 | tr = 0; | |
347 | else if (mag <= dqthr) /* supposed data, but small mag */ | |
348 | tr = 0; /* treated as voice */ | |
349 | else /* signal is data (modem) */ | |
350 | tr = 1; | |
351 | ||
352 | /* | |
353 | * Quantizer scale factor adaptation. | |
354 | */ | |
355 | ||
356 | /* FUNCTW & FILTD & DELAY */ | |
357 | /* update non-steady state step size multiplier */ | |
358 | state_ptr->yu = y + ((wi - y) >> 5); | |
359 | ||
360 | /* LIMB */ | |
361 | if (state_ptr->yu < 544) /* 544 <= yu <= 5120 */ | |
362 | state_ptr->yu = 544; | |
363 | else if (state_ptr->yu > 5120) | |
364 | state_ptr->yu = 5120; | |
365 | ||
366 | /* FILTE & DELAY */ | |
367 | /* update steady state step size multiplier */ | |
368 | state_ptr->yl += state_ptr->yu + ((-state_ptr->yl) >> 6); | |
369 | ||
370 | /* | |
371 | * Adaptive predictor coefficients. | |
372 | */ | |
373 | if (tr == 1) { /* reset a's and b's for modem signal */ | |
374 | state_ptr->a[0] = 0; | |
375 | state_ptr->a[1] = 0; | |
376 | state_ptr->b[0] = 0; | |
377 | state_ptr->b[1] = 0; | |
378 | state_ptr->b[2] = 0; | |
379 | state_ptr->b[3] = 0; | |
380 | state_ptr->b[4] = 0; | |
381 | state_ptr->b[5] = 0; | |
382 | ||
383 | a2p = 0; /* eliminate Compiler Warnings */ | |
384 | } else { /* update a's and b's */ | |
385 | pks1 = pk0 ^ state_ptr->pk[0]; /* UPA2 */ | |
386 | ||
387 | /* update predictor pole a[1] */ | |
388 | a2p = state_ptr->a[1] - (state_ptr->a[1] >> 7); | |
389 | if (dqsez != 0) { | |
390 | fa1 = (pks1) ? state_ptr->a[0] : -state_ptr->a[0]; | |
391 | if (fa1 < -8191) /* a2p = function of fa1 */ | |
392 | a2p -= 0x100; | |
393 | else if (fa1 > 8191) | |
394 | a2p += 0xFF; | |
395 | else | |
396 | a2p += fa1 >> 5; | |
397 | ||
398 | if (pk0 ^ state_ptr->pk[1]) | |
399 | /* LIMC */ | |
400 | if (a2p <= -12160) | |
401 | a2p = -12288; | |
402 | else if (a2p >= 12416) | |
403 | a2p = 12288; | |
404 | else | |
405 | a2p -= 0x80; | |
406 | else if (a2p <= -12416) | |
407 | a2p = -12288; | |
408 | else if (a2p >= 12160) | |
409 | a2p = 12288; | |
410 | else | |
411 | a2p += 0x80; | |
412 | } | |
413 | ||
414 | /* TRIGB & DELAY */ | |
415 | state_ptr->a[1] = a2p; | |
416 | ||
417 | /* UPA1 */ | |
418 | /* update predictor pole a[0] */ | |
419 | state_ptr->a[0] -= state_ptr->a[0] >> 8; | |
420 | if (dqsez != 0) | |
421 | if (pks1 == 0) | |
422 | state_ptr->a[0] += 192; | |
423 | else | |
424 | state_ptr->a[0] -= 192; | |
425 | ||
426 | /* LIMD */ | |
427 | a1ul = 15360 - a2p; | |
428 | if (state_ptr->a[0] < -a1ul) | |
429 | state_ptr->a[0] = -a1ul; | |
430 | else if (state_ptr->a[0] > a1ul) | |
431 | state_ptr->a[0] = a1ul; | |
432 | ||
433 | /* UPB : update predictor zeros b[6] */ | |
434 | for (cnt = 0; cnt < 6; cnt++) { | |
435 | if (code_size == 5) /* for 40Kbps G.723 */ | |
436 | state_ptr->b[cnt] -= state_ptr->b[cnt] >> 9; | |
437 | else /* for G.721 and 24Kbps G.723 */ | |
438 | state_ptr->b[cnt] -= state_ptr->b[cnt] >> 8; | |
439 | if (dq & 0x7FFF) { /* XOR */ | |
440 | if ((dq ^ state_ptr->dq[cnt]) >= 0) | |
441 | state_ptr->b[cnt] += 128; | |
442 | else | |
443 | state_ptr->b[cnt] -= 128; | |
444 | } | |
445 | } | |
446 | } | |
447 | ||
448 | for (cnt = 5; cnt > 0; cnt--) | |
449 | state_ptr->dq[cnt] = state_ptr->dq[cnt-1]; | |
450 | /* FLOAT A : convert dq[0] to 4-bit exp, 6-bit mantissa f.p. */ | |
451 | if (mag == 0) { | |
452 | state_ptr->dq[0] = (dq >= 0) ? 0x20 : 0xFC20; | |
453 | } else { | |
454 | state_ptr->dq[0] = (dq >= 0) ? | |
455 | base2 (mag) : base2 (mag) - 0x400; | |
456 | } | |
457 | ||
458 | state_ptr->sr[1] = state_ptr->sr[0]; | |
459 | /* FLOAT B : convert sr to 4-bit exp., 6-bit mantissa f.p. */ | |
460 | if (sr == 0) { | |
461 | state_ptr->sr[0] = 0x20; | |
462 | } else if (sr > 0) { | |
463 | state_ptr->sr[0] = base2(sr); | |
464 | } else if (sr > -32768) { | |
465 | mag = -sr; | |
466 | state_ptr->sr[0] = base2(mag) - 0x400; | |
467 | } else | |
468 | state_ptr->sr[0] = short (0xFC20); | |
469 | ||
470 | /* DELAY A */ | |
471 | state_ptr->pk[1] = state_ptr->pk[0]; | |
472 | state_ptr->pk[0] = pk0; | |
473 | ||
474 | /* TONE */ | |
475 | if (tr == 1) /* this sample has been treated as data */ | |
476 | state_ptr->td = 0; /* next one will be treated as voice */ | |
477 | else if (a2p < -11776) /* small sample-to-sample correlation */ | |
478 | state_ptr->td = 1; /* signal may be data */ | |
479 | else /* signal is voice */ | |
480 | state_ptr->td = 0; | |
481 | ||
482 | /* | |
483 | * Adaptation speed control. | |
484 | */ | |
485 | state_ptr->dms += (fi - state_ptr->dms) >> 5; /* FILTA */ | |
486 | state_ptr->dml += (((fi << 2) - state_ptr->dml) >> 7); /* FILTB */ | |
487 | ||
488 | if (tr == 1) | |
489 | state_ptr->ap = 256; | |
490 | else if (y < 1536) /* SUBTC */ | |
491 | state_ptr->ap += (0x200 - state_ptr->ap) >> 4; | |
492 | else if (state_ptr->td == 1) | |
493 | state_ptr->ap += (0x200 - state_ptr->ap) >> 4; | |
494 | else if (abs((state_ptr->dms << 2) - state_ptr->dml) >= | |
495 | (state_ptr->dml >> 3)) | |
496 | state_ptr->ap += (0x200 - state_ptr->ap) >> 4; | |
497 | else | |
498 | state_ptr->ap += (-state_ptr->ap) >> 4; | |
499 | } | |
500 | ||
501 | /* | |
502 | * tandem_adjust(sr, se, y, i, sign) | |
503 | * | |
504 | * At the end of ADPCM decoding, it simulates an encoder which may be receiving | |
505 | * the output of this decoder as a tandem process. If the output of the | |
506 | * simulated encoder differs from the input to this decoder, the decoder output | |
507 | * is adjusted by one level of A-law or u-law codes. | |
508 | * | |
509 | * Input: | |
510 | * sr decoder output linear PCM sample, | |
511 | * se predictor estimate sample, | |
512 | * y quantizer step size, | |
513 | * i decoder input code, | |
514 | * sign sign bit of code i | |
515 | * | |
516 | * Return: | |
517 | * adjusted A-law or u-law compressed sample. | |
518 | */ | |
519 | int | |
520 | tandem_adjust_alaw( | |
521 | int sr, /* decoder output linear PCM sample */ | |
522 | int se, /* predictor estimate sample */ | |
523 | int y, /* quantizer step size */ | |
524 | int i, /* decoder input code */ | |
525 | int sign, | |
526 | short *qtab) | |
527 | { | |
528 | unsigned char sp; /* A-law compressed 8-bit code */ | |
529 | short dx; /* prediction error */ | |
530 | char id; /* quantized prediction error */ | |
531 | int sd; /* adjusted A-law decoded sample value */ | |
532 | int im; /* biased magnitude of i */ | |
533 | int imx; /* biased magnitude of id */ | |
534 | ||
535 | if (sr <= -32768) | |
536 | sr = -1; | |
537 | sp = linear2alaw((sr >> 1) << 3); /* short to A-law compression */ | |
538 | dx = (alaw2linear(sp) >> 2) - se; /* 16-bit prediction error */ | |
539 | id = quantize(dx, y, qtab, sign - 1); | |
540 | ||
541 | if (id == i) { /* no adjustment on sp */ | |
542 | return (sp); | |
543 | } else { /* sp adjustment needed */ | |
544 | /* ADPCM codes : 8, 9, ... F, 0, 1, ... , 6, 7 */ | |
545 | im = i ^ sign; /* 2's complement to biased unsigned */ | |
546 | imx = id ^ sign; | |
547 | ||
548 | if (imx > im) { /* sp adjusted to next lower value */ | |
549 | if (sp & 0x80) { | |
550 | sd = (sp == 0xD5) ? 0x55 : | |
551 | ((sp ^ 0x55) - 1) ^ 0x55; | |
552 | } else { | |
553 | sd = (sp == 0x2A) ? 0x2A : | |
554 | ((sp ^ 0x55) + 1) ^ 0x55; | |
555 | } | |
556 | } else { /* sp adjusted to next higher value */ | |
557 | if (sp & 0x80) | |
558 | sd = (sp == 0xAA) ? 0xAA : | |
559 | ((sp ^ 0x55) + 1) ^ 0x55; | |
560 | else | |
561 | sd = (sp == 0x55) ? 0xD5 : | |
562 | ((sp ^ 0x55) - 1) ^ 0x55; | |
563 | } | |
564 | return (sd); | |
565 | } | |
566 | } | |
567 | ||
568 | int | |
569 | tandem_adjust_ulaw( | |
570 | int sr, /* decoder output linear PCM sample */ | |
571 | int se, /* predictor estimate sample */ | |
572 | int y, /* quantizer step size */ | |
573 | int i, /* decoder input code */ | |
574 | int sign, | |
575 | short *qtab) | |
576 | { | |
577 | unsigned char sp; /* u-law compressed 8-bit code */ | |
578 | short dx; /* prediction error */ | |
579 | char id; /* quantized prediction error */ | |
580 | int sd; /* adjusted u-law decoded sample value */ | |
581 | int im; /* biased magnitude of i */ | |
582 | int imx; /* biased magnitude of id */ | |
583 | ||
584 | if (sr <= -32768) | |
585 | sr = 0; | |
586 | sp = linear2ulaw(sr << 2); /* short to u-law compression */ | |
587 | dx = (ulaw2linear(sp) >> 2) - se; /* 16-bit prediction error */ | |
588 | id = quantize(dx, y, qtab, sign - 1); | |
589 | if (id == i) { | |
590 | return (sp); | |
591 | } else { | |
592 | /* ADPCM codes : 8, 9, ... F, 0, 1, ... , 6, 7 */ | |
593 | im = i ^ sign; /* 2's complement to biased unsigned */ | |
594 | imx = id ^ sign; | |
595 | if (imx > im) { /* sp adjusted to next lower value */ | |
596 | if (sp & 0x80) | |
597 | sd = (sp == 0xFF) ? 0x7E : sp + 1; | |
598 | else | |
599 | sd = (sp == 0) ? 0 : sp - 1; | |
600 | ||
601 | } else { /* sp adjusted to next higher value */ | |
602 | if (sp & 0x80) | |
603 | sd = (sp == 0x80) ? 0x80 : sp - 1; | |
604 | else | |
605 | sd = (sp == 0x7F) ? 0xFE : sp + 1; | |
606 | } | |
607 | return (sd); | |
608 | } | |
609 | } |