Bug Summary

File:libs/libsndfile/src/ALAC/alac_decoder.c
Location:line 355, column 5
Description:Value stored to 'shift' is never read

Annotated Source Code

1/*
2 * Copyright (c) 2011 Apple Inc. All rights reserved.
3 * Copyright (C) 2012-2013 Erik de Castro Lopo <erikd@mega-nerd.com>
4 *
5 * @APPLE_APACHE_LICENSE_HEADER_START@
6 *
7 * Licensed under the Apache License, Version 2.0 (the "License");
8 * you may not use this file except in compliance with the License.
9 * You may obtain a copy of the License at
10 *
11 * http://www.apache.org/licenses/LICENSE-2.0
12 *
13 * Unless required by applicable law or agreed to in writing, software
14 * distributed under the License is distributed on an "AS IS" BASIS,
15 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
16 * See the License for the specific language governing permissions and
17 * limitations under the License.
18 *
19 * @APPLE_APACHE_LICENSE_HEADER_END@
20 */
21
22/*
23 File: ALACDecoder.cpp
24*/
25
26#include <stdlib.h>
27#include <stddef.h>
28#include <string.h>
29
30#include "alac_codec.h"
31
32#include "dplib.h"
33#include "aglib.h"
34#include "matrixlib.h"
35
36#include "ALACBitUtilities.h"
37#include "EndianPortable.h"
38
39typedef enum
40{ false = 0,
41 true = 1
42} bool ;
43
44// constants/data
45const uint32_t kMaxBitDepth = 32; // max allowed bit depth is 32
46
47
48// prototypes
49static int32_t alac_fill_element (struct BitBuffer * bits) ;
50static int32_t alac_data_stream_element (struct BitBuffer * bits) ;
51
52static void Zero32( int32_t * buffer, uint32_t numItems, uint32_t stride );
53
54
55/*
56 Init()
57 - initialize the decoder with the given configuration
58*/
59int32_t
60alac_decoder_init (ALAC_DECODER *p, void * inMagicCookie, uint32_t inMagicCookieSize)
61{
62 int32_t status = ALAC_noErr;
63 ALACSpecificConfig theConfig;
64 uint8_t * theActualCookie = (uint8_t *)inMagicCookie;
65 uint32_t theCookieBytesRemaining = inMagicCookieSize;
66
67 // For historical reasons the decoder needs to be resilient to magic cookies vended by older encoders.
68 // As specified in the ALACMagicCookieDescription.txt document, there may be additional data encapsulating
69 // the ALACSpecificConfig. This would consist of format ('frma') and 'alac' atoms which precede the
70 // ALACSpecificConfig.
71 // See ALACMagicCookieDescription.txt for additional documentation concerning the 'magic cookie'
72
73 // skip format ('frma') atom if present
74 if (theActualCookie[4] == 'f' && theActualCookie[5] == 'r' && theActualCookie[6] == 'm' && theActualCookie[7] == 'a')
75 {
76 theActualCookie += 12;
77 theCookieBytesRemaining -= 12;
78 }
79
80 // skip 'alac' atom header if present
81 if (theActualCookie[4] == 'a' && theActualCookie[5] == 'l' && theActualCookie[6] == 'a' && theActualCookie[7] == 'c')
82 {
83 theActualCookie += 12;
84 theCookieBytesRemaining -= 12;
85 }
86
87 // read the ALACSpecificConfig
88 if (theCookieBytesRemaining >= sizeof(ALACSpecificConfig))
89 {
90 theConfig.frameLength = psf_get_be32 (theActualCookie, offsetof (ALACSpecificConfig, frameLength)__builtin_offsetof(ALACSpecificConfig, frameLength)) ;
91
92 if (theConfig.frameLength > ALAC_FRAME_LENGTH4096)
93 return fALAC_FrameLengthError ;
94
95 theConfig.compatibleVersion = theActualCookie [offsetof (ALACSpecificConfig, compatibleVersion)__builtin_offsetof(ALACSpecificConfig, compatibleVersion)] ;
96 theConfig.bitDepth = theActualCookie [offsetof (ALACSpecificConfig, bitDepth)__builtin_offsetof(ALACSpecificConfig, bitDepth)] ;
97 theConfig.pb = theActualCookie [offsetof (ALACSpecificConfig, pb)__builtin_offsetof(ALACSpecificConfig, pb)] ;
98 theConfig.mb = theActualCookie [offsetof (ALACSpecificConfig, mb)__builtin_offsetof(ALACSpecificConfig, mb)] ;
99 theConfig.kb = theActualCookie [offsetof (ALACSpecificConfig, kb)__builtin_offsetof(ALACSpecificConfig, kb)] ;
100 theConfig.numChannels = theActualCookie [offsetof (ALACSpecificConfig, numChannels)__builtin_offsetof(ALACSpecificConfig, numChannels)] ;
101 theConfig.maxRun = psf_get_be16 (theActualCookie, offsetof (ALACSpecificConfig, maxRun)__builtin_offsetof(ALACSpecificConfig, maxRun)) ;
102 theConfig.maxFrameBytes = psf_get_be32 (theActualCookie, offsetof (ALACSpecificConfig, maxFrameBytes)__builtin_offsetof(ALACSpecificConfig, maxFrameBytes)) ;
103 theConfig.avgBitRate = psf_get_be32 (theActualCookie, offsetof (ALACSpecificConfig, avgBitRate)__builtin_offsetof(ALACSpecificConfig, avgBitRate)) ;
104 theConfig.sampleRate = psf_get_be32 (theActualCookie, offsetof (ALACSpecificConfig, sampleRate)__builtin_offsetof(ALACSpecificConfig, sampleRate)) ;
105
106 p->mConfig = theConfig;
107
108 RequireAction( p->mConfig.compatibleVersion <= kALACVersion, return kALAC_ParamError; )if (!(p->mConfig.compatibleVersion <= kALACVersion)) { return
kALAC_ParamError; };
109
110 RequireAction( (p->mMixBufferU != NULL) && (p->mMixBufferV != NULL) && (p->mPredictor != NULL),if (!((p->mMixBufferU != ((void*)0)) && (p->mMixBufferV
!= ((void*)0)) && (p->mPredictor != ((void*)0))))
{ status = kALAC_MemFullError; goto Exit; }
111 status = kALAC_MemFullError; goto Exit; )if (!((p->mMixBufferU != ((void*)0)) && (p->mMixBufferV
!= ((void*)0)) && (p->mPredictor != ((void*)0))))
{ status = kALAC_MemFullError; goto Exit; };
112 }
113 else
114 {
115 status = kALAC_ParamError;
116 }
117
118 // skip to Channel Layout Info
119 // theActualCookie += sizeof(ALACSpecificConfig);
120
121 // Currently, the Channel Layout Info portion of the magic cookie (as defined in the
122 // ALACMagicCookieDescription.txt document) is unused by the decoder.
123
124Exit:
125 return status;
126}
127
128/*
129 Decode()
130 - the decoded samples are interleaved into the output buffer in the order they arrive in
131 the bitstream
132*/
133int32_t
134alac_decode (ALAC_DECODER *p, struct BitBuffer * bits, int32_t * sampleBuffer, uint32_t numSamples, uint32_t numChannels, uint32_t * outNumSamples)
135{
136 BitBuffer shiftBits;
137 uint32_t bits1, bits2;
138 uint8_t tag;
139 uint8_t elementInstanceTag;
140 AGParamRec agParams;
141 uint32_t channelIndex;
142 int16_t coefsU[32]; // max possible size is 32 although NUMCOEPAIRS is the current limit
143 int16_t coefsV[32];
144 uint8_t numU, numV;
145 uint8_t mixBits;
146 int8_t mixRes;
147 uint16_t unusedHeader;
148 uint8_t escapeFlag;
149 uint32_t chanBits;
150 uint8_t bytesShifted;
151 uint32_t shift;
152 uint8_t modeU, modeV;
153 uint32_t denShiftU, denShiftV;
154 uint16_t pbFactorU, pbFactorV;
155 uint16_t pb;
156 int32_t * out32;
157 uint8_t headerByte;
158 uint8_t partialFrame;
159 uint32_t extraBits;
160 int32_t val;
161 uint32_t i, j;
162 int32_t status;
163
164 RequireAction( (bits != NULL) && (sampleBuffer != NULL) && (outNumSamples != NULL), return kALAC_ParamError; )if (!((bits != ((void*)0)) && (sampleBuffer != ((void
*)0)) && (outNumSamples != ((void*)0)))) { return kALAC_ParamError
; };
165 RequireAction( numChannels > 0, return kALAC_ParamError; )if (!(numChannels > 0)) { return kALAC_ParamError; };
166
167 p->mActiveElements = 0;
168 channelIndex = 0;
169
170 status = ALAC_noErr;
171 *outNumSamples = numSamples;
172
173 while ( status == ALAC_noErr )
174 {
175 // bail if we ran off the end of the buffer
176 RequireAction( bits->cur < bits->end, status = kALAC_ParamError; goto Exit; )if (!(bits->cur < bits->end)) { status = kALAC_ParamError
; goto Exit; };
177
178 // copy global decode params for this element
179 pb = p->mConfig.pb;
180
181 // read element tag
182 tag = BitBufferReadSmall( bits, 3 );
183 switch ( tag )
184 {
185 case ID_SCE:
186 case ID_LFE:
187 {
188 // mono/LFE channel
189 elementInstanceTag = BitBufferReadSmall( bits, 4 );
190 p->mActiveElements |= (1u << elementInstanceTag);
191
192 // read the 12 unused header bits
193 unusedHeader = (uint16_t) BitBufferRead( bits, 12 );
194 RequireAction( unusedHeader == 0, status = kALAC_ParamError; goto Exit; )if (!(unusedHeader == 0)) { status = kALAC_ParamError; goto Exit
; };
195
196 // read the 1-bit "partial frame" flag, 2-bit "shift-off" flag & 1-bit "escape" flag
197 headerByte = (uint8_t) BitBufferRead( bits, 4 );
198
199 partialFrame = headerByte >> 3;
200
201 bytesShifted = (headerByte >> 1) & 0x3u;
202 RequireAction( bytesShifted != 3, status = kALAC_ParamError; goto Exit; )if (!(bytesShifted != 3)) { status = kALAC_ParamError; goto Exit
; };
203
204 shift = bytesShifted * 8;
205
206 escapeFlag = headerByte & 0x1;
207
208 chanBits = p->mConfig.bitDepth - (bytesShifted * 8);
209
210 // check for partial frame to override requested numSamples
211 if ( partialFrame != 0 )
212 {
213 numSamples = BitBufferRead( bits, 16 ) << 16;
214 numSamples |= BitBufferRead( bits, 16 );
215 }
216
217 if ( escapeFlag == 0 )
218 {
219 // compressed frame, read rest of parameters
220 mixBits = (uint8_t) BitBufferRead( bits, 8 );
221 mixRes = (int8_t) BitBufferRead( bits, 8 );
222 //Assert( (mixBits == 0) && (mixRes == 0) ); // no mixing for mono
223
224 headerByte = (uint8_t) BitBufferRead( bits, 8 );
225 modeU = headerByte >> 4;
226 denShiftU = headerByte & 0xfu;
227
228 headerByte = (uint8_t) BitBufferRead( bits, 8 );
229 pbFactorU = headerByte >> 5;
230 numU = headerByte & 0x1fu;
231
232 for ( i = 0; i < numU; i++ )
233 coefsU[i] = (int16_t) BitBufferRead( bits, 16 );
234
235 // if shift active, skip the the shift buffer but remember where it starts
236 if ( bytesShifted != 0 )
237 {
238 shiftBits = *bits;
239 BitBufferAdvance( bits, (bytesShifted * 8) * numSamples );
240 }
241
242 // decompress
243 set_ag_params( &agParams, p->mConfig.mb, (pb * pbFactorU) / 4, p->mConfig.kb, numSamples, numSamples, p->mConfig.maxRun );
244 status = dyn_decomp( &agParams, bits, p->mPredictor, numSamples, chanBits, &bits1 );
245 RequireNoErr( status, goto Exit; )if ((status)) { goto Exit; };
246
247 if ( modeU == 0 )
248 {
249 unpc_block( p->mPredictor, p->mMixBufferU, numSamples, &coefsU[0], numU, chanBits, denShiftU );
250 }
251 else
252 {
253 // the special "numActive == 31" mode can be done in-place
254 unpc_block( p->mPredictor, p->mPredictor, numSamples, NULL((void*)0), 31, chanBits, 0 );
255 unpc_block( p->mPredictor, p->mMixBufferU, numSamples, &coefsU[0], numU, chanBits, denShiftU );
256 }
257 }
258 else
259 {
260 //Assert( bytesShifted == 0 );
261
262 // uncompressed frame, copy data into the mix buffer to use common output code
263 shift = 32 - chanBits;
264 if ( chanBits <= 16 )
265 {
266 for ( i = 0; i < numSamples; i++ )
267 {
268 val = (int32_t) BitBufferRead( bits, (uint8_t) chanBits );
269 val = (val << shift) >> shift;
270 p->mMixBufferU[i] = val;
271 }
272 }
273 else
274 {
275 // BitBufferRead() can't read more than 16 bits at a time so break up the reads
276 extraBits = chanBits - 16;
277 for ( i = 0; i < numSamples; i++ )
278 {
279 val = (int32_t) BitBufferRead( bits, 16 );
280 val = (val << 16) >> shift;
281 p->mMixBufferU[i] = val | BitBufferRead( bits, (uint8_t) extraBits );
282 }
283 }
284
285 mixBits = mixRes = 0;
286 bits1 = chanBits * numSamples;
287 bytesShifted = 0;
288 }
289
290 // now read the shifted values into the shift buffer
291 if ( bytesShifted != 0 )
292 {
293 shift = bytesShifted * 8;
294 //Assert( shift <= 16 );
295
296 for ( i = 0; i < numSamples; i++ )
297 p->mShiftBuffer[i] = (uint16_t) BitBufferRead( &shiftBits, (uint8_t) shift );
298 }
299
300 // convert 32-bit integers into output buffer
301 switch ( p->mConfig.bitDepth )
302 {
303 case 16:
304 out32 = sampleBuffer + channelIndex;
305 for ( i = 0, j = 0; i < numSamples; i++, j += numChannels )
306 out32[j] = p->mMixBufferU[i] << 16;
307 break;
308 case 20:
309 out32 = sampleBuffer + channelIndex;
310 copyPredictorTo20( p->mMixBufferU, out32, numChannels, numSamples );
311 break;
312 case 24:
313 out32 = sampleBuffer + channelIndex;
314 if ( bytesShifted != 0 )
315 copyPredictorTo24Shift( p->mMixBufferU, p->mShiftBuffer, out32, numChannels, numSamples, bytesShifted );
316 else
317 copyPredictorTo24( p->mMixBufferU, out32, numChannels, numSamples );
318 break;
319 case 32:
320 out32 = sampleBuffer + channelIndex;
321 if ( bytesShifted != 0 )
322 copyPredictorTo32Shift( p->mMixBufferU, p->mShiftBuffer, out32, numChannels, numSamples, bytesShifted );
323 else
324 copyPredictorTo32( p->mMixBufferU, out32, numChannels, numSamples);
325 break;
326 }
327
328 channelIndex += 1;
329 *outNumSamples = numSamples;
330 break;
331 }
332
333 case ID_CPE:
334 {
335 // if decoding this pair would take us over the max channels limit, bail
336 if ( (channelIndex + 2) > numChannels )
337 goto NoMoreChannels;
338
339 // stereo channel pair
340 elementInstanceTag = BitBufferReadSmall( bits, 4 );
341 p->mActiveElements |= (1u << elementInstanceTag);
342
343 // read the 12 unused header bits
344 unusedHeader = (uint16_t) BitBufferRead( bits, 12 );
345 RequireAction( unusedHeader == 0, status = kALAC_ParamError; goto Exit; )if (!(unusedHeader == 0)) { status = kALAC_ParamError; goto Exit
; };
346
347 // read the 1-bit "partial frame" flag, 2-bit "shift-off" flag & 1-bit "escape" flag
348 headerByte = (uint8_t) BitBufferRead( bits, 4 );
349
350 partialFrame = headerByte >> 3;
351
352 bytesShifted = (headerByte >> 1) & 0x3u;
353 RequireAction( bytesShifted != 3, status = kALAC_ParamError; goto Exit; )if (!(bytesShifted != 3)) { status = kALAC_ParamError; goto Exit
; };
354
355 shift = bytesShifted * 8;
Value stored to 'shift' is never read
356
357 escapeFlag = headerByte & 0x1;
358
359 chanBits = p->mConfig.bitDepth - (bytesShifted * 8) + 1;
360
361 // check for partial frame length to override requested numSamples
362 if ( partialFrame != 0 )
363 {
364 numSamples = BitBufferRead( bits, 16 ) << 16;
365 numSamples |= BitBufferRead( bits, 16 );
366 }
367
368 if ( escapeFlag == 0 )
369 {
370 // compressed frame, read rest of parameters
371 mixBits = (uint8_t) BitBufferRead( bits, 8 );
372 mixRes = (int8_t) BitBufferRead( bits, 8 );
373
374 headerByte = (uint8_t) BitBufferRead( bits, 8 );
375 modeU = headerByte >> 4;
376 denShiftU = headerByte & 0xfu;
377
378 headerByte = (uint8_t) BitBufferRead( bits, 8 );
379 pbFactorU = headerByte >> 5;
380 numU = headerByte & 0x1fu;
381 for ( i = 0; i < numU; i++ )
382 coefsU[i] = (int16_t) BitBufferRead( bits, 16 );
383
384 headerByte = (uint8_t) BitBufferRead( bits, 8 );
385 modeV = headerByte >> 4;
386 denShiftV = headerByte & 0xfu;
387
388 headerByte = (uint8_t) BitBufferRead( bits, 8 );
389 pbFactorV = headerByte >> 5;
390 numV = headerByte & 0x1fu;
391 for ( i = 0; i < numV; i++ )
392 coefsV[i] = (int16_t) BitBufferRead( bits, 16 );
393
394 // if shift active, skip the interleaved shifted values but remember where they start
395 if ( bytesShifted != 0 )
396 {
397 shiftBits = *bits;
398 BitBufferAdvance( bits, (bytesShifted * 8) * 2 * numSamples );
399 }
400
401 // decompress and run predictor for "left" channel
402 set_ag_params( &agParams, p->mConfig.mb, (pb * pbFactorU) / 4, p->mConfig.kb, numSamples, numSamples, p->mConfig.maxRun );
403 status = dyn_decomp( &agParams, bits, p->mPredictor, numSamples, chanBits, &bits1 );
404 RequireNoErr( status, goto Exit; )if ((status)) { goto Exit; };
405
406 if ( modeU == 0 )
407 {
408 unpc_block( p->mPredictor, p->mMixBufferU, numSamples, &coefsU[0], numU, chanBits, denShiftU );
409 }
410 else
411 {
412 // the special "numActive == 31" mode can be done in-place
413 unpc_block( p->mPredictor, p->mPredictor, numSamples, NULL((void*)0), 31, chanBits, 0 );
414 unpc_block( p->mPredictor, p->mMixBufferU, numSamples, &coefsU[0], numU, chanBits, denShiftU );
415 }
416
417 // decompress and run predictor for "right" channel
418 set_ag_params( &agParams, p->mConfig.mb, (pb * pbFactorV) / 4, p->mConfig.kb, numSamples, numSamples, p->mConfig.maxRun );
419 status = dyn_decomp( &agParams, bits, p->mPredictor, numSamples, chanBits, &bits2 );
420 RequireNoErr( status, goto Exit; )if ((status)) { goto Exit; };
421
422 if ( modeV == 0 )
423 {
424 unpc_block( p->mPredictor, p->mMixBufferV, numSamples, &coefsV[0], numV, chanBits, denShiftV );
425 }
426 else
427 {
428 // the special "numActive == 31" mode can be done in-place
429 unpc_block( p->mPredictor, p->mPredictor, numSamples, NULL((void*)0), 31, chanBits, 0 );
430 unpc_block( p->mPredictor, p->mMixBufferV, numSamples, &coefsV[0], numV, chanBits, denShiftV );
431 }
432 }
433 else
434 {
435 //Assert( bytesShifted == 0 );
436
437 // uncompressed frame, copy data into the mix buffers to use common output code
438 chanBits = p->mConfig.bitDepth;
439 shift = 32 - chanBits;
440 if ( chanBits <= 16 )
441 {
442 for ( i = 0; i < numSamples; i++ )
443 {
444 val = (int32_t) BitBufferRead( bits, (uint8_t) chanBits );
445 val = (val << shift) >> shift;
446 p->mMixBufferU[i] = val;
447
448 val = (int32_t) BitBufferRead( bits, (uint8_t) chanBits );
449 val = (val << shift) >> shift;
450 p->mMixBufferV[i] = val;
451 }
452 }
453 else
454 {
455 // BitBufferRead() can't read more than 16 bits at a time so break up the reads
456 extraBits = chanBits - 16;
457 for ( i = 0; i < numSamples; i++ )
458 {
459 val = (int32_t) BitBufferRead( bits, 16 );
460 val = (val << 16) >> shift;
461 p->mMixBufferU[i] = val | BitBufferRead( bits, (uint8_t)extraBits );
462
463 val = (int32_t) BitBufferRead( bits, 16 );
464 val = (val << 16) >> shift;
465 p->mMixBufferV[i] = val | BitBufferRead( bits, (uint8_t)extraBits );
466 }
467 }
468
469 bits1 = chanBits * numSamples;
470 bits2 = chanBits * numSamples;
471 mixBits = mixRes = 0;
472 bytesShifted = 0;
473 }
474
475 // now read the shifted values into the shift buffer
476 if ( bytesShifted != 0 )
477 {
478 shift = bytesShifted * 8;
479 //Assert( shift <= 16 );
480
481 for ( i = 0; i < (numSamples * 2); i += 2 )
482 {
483 p->mShiftBuffer[i + 0] = (uint16_t) BitBufferRead( &shiftBits, (uint8_t) shift );
484 p->mShiftBuffer[i + 1] = (uint16_t) BitBufferRead( &shiftBits, (uint8_t) shift );
485 }
486 }
487
488 // un-mix the data and convert to output format
489 // - note that mixRes = 0 means just interleave so we use that path for uncompressed frames
490 switch ( p->mConfig.bitDepth )
491 {
492 case 16:
493 out32 = sampleBuffer + channelIndex;
494 unmix16( p->mMixBufferU, p->mMixBufferV, out32, numChannels, numSamples, mixBits, mixRes );
495 break;
496 case 20:
497 out32 = sampleBuffer + channelIndex;
498 unmix20( p->mMixBufferU, p->mMixBufferV, out32, numChannels, numSamples, mixBits, mixRes );
499 break;
500 case 24:
501 out32 = sampleBuffer + channelIndex;
502 unmix24( p->mMixBufferU, p->mMixBufferV, out32, numChannels, numSamples,
503 mixBits, mixRes, p->mShiftBuffer, bytesShifted );
504 break;
505 case 32:
506 out32 = sampleBuffer + channelIndex;
507 unmix32( p->mMixBufferU, p->mMixBufferV, out32, numChannels, numSamples,
508 mixBits, mixRes, p->mShiftBuffer, bytesShifted );
509 break;
510 }
511
512 channelIndex += 2;
513 *outNumSamples = numSamples;
514 break;
515 }
516
517 case ID_CCE:
518 case ID_PCE:
519 {
520 // unsupported element, bail
521 //AssertNoErr( tag );
522 status = kALAC_ParamError;
523 break;
524 }
525
526 case ID_DSE:
527 {
528 // data stream element -- parse but ignore
529 status = alac_data_stream_element (bits) ;
530 break;
531 }
532
533 case ID_FIL:
534 {
535 // fill element -- parse but ignore
536 status = alac_fill_element (bits) ;
537 break;
538 }
539
540 case ID_END:
541 {
542 // frame end, all done so byte align the frame and check for overruns
543 BitBufferByteAlign( bits, false );
544 //Assert( bits->cur == bits->end );
545 goto Exit;
546 }
547 }
548
549#if 0 // ! DEBUG
550 // if we've decoded all of our channels, bail (but not in debug b/c we want to know if we're seeing bad bits)
551 // - this also protects us if the config does not match the bitstream or crap data bits follow the audio bits
552 if ( channelIndex >= numChannels )
553 break;
554#endif
555 }
556
557NoMoreChannels:
558
559 // if we get here and haven't decoded all of the requested channels, fill the remaining channels with zeros
560 for ( ; channelIndex < numChannels; channelIndex++ )
561 {
562 int32_t * fill32 = sampleBuffer + channelIndex;
563 Zero32( fill32, numSamples, numChannels );
564 }
565
566Exit:
567 return status;
568}
569
570#if PRAGMA_MARK0
571#pragma mark -
572#endif
573
574/*
575 FillElement()
576 - they're just filler so we don't need 'em
577*/
578static int32_t
579alac_fill_element (struct BitBuffer * bits)
580{
581 int16_t count;
582
583 // 4-bit count or (4-bit + 8-bit count) if 4-bit count == 15
584 // - plus this weird -1 thing I still don't fully understand
585 count = BitBufferReadSmall( bits, 4 );
586 if ( count == 15 )
587 count += (int16_t) BitBufferReadSmall( bits, 8 ) - 1;
588
589 BitBufferAdvance( bits, count * 8 );
590
591 RequireAction( bits->cur <= bits->end, return kALAC_ParamError; )if (!(bits->cur <= bits->end)) { return kALAC_ParamError
; };
592
593 return ALAC_noErr;
594}
595
596/*
597 DataStreamElement()
598 - we don't care about data stream elements so just skip them
599*/
600static int32_t
601alac_data_stream_element (struct BitBuffer * bits)
602{
603 int32_t data_byte_align_flag;
604 uint16_t count;
605
606 // the tag associates this data stream element with a given audio element
607
608 /* element_instance_tag = */ BitBufferReadSmall( bits, 4 );
609
610 data_byte_align_flag = BitBufferReadOne( bits );
611
612 // 8-bit count or (8-bit + 8-bit count) if 8-bit count == 255
613 count = BitBufferReadSmall( bits, 8 );
614 if ( count == 255 )
615 count += BitBufferReadSmall( bits, 8 );
616
617 // the align flag means the bitstream should be byte-aligned before reading the following data bytes
618 if ( data_byte_align_flag )
619 BitBufferByteAlign( bits, false );
620
621 // skip the data bytes
622 BitBufferAdvance( bits, count * 8 );
623
624 RequireAction( bits->cur <= bits->end, return kALAC_ParamError; )if (!(bits->cur <= bits->end)) { return kALAC_ParamError
; };
625
626 return ALAC_noErr;
627}
628
629/*
630 ZeroN()
631 - helper routines to clear out output channel buffers when decoding fewer channels than requested
632*/
633static void Zero32( int32_t * buffer, uint32_t numItems, uint32_t stride )
634{
635 uint32_t indx;
636
637 if ( stride == 1 )
638 {
639 memset( buffer, 0, numItems * sizeof(int32_t) );
640 }
641 else
642 {
643 for ( indx = 0; indx < (numItems * stride); indx += stride )
644 buffer[indx] = 0;
645 }
646}