src/share/grabbag/replaygain.c

   1 /* grabbag - Convenience lib for various routines common to several tools
   2  * Copyright (C) 2002,2003  Josh Coalson
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License
   6  * as published by the Free Software Foundation; either version 2
   7  * of the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  17  */
  18
  19 #include "share/grabbag.h"
  20 #include "share/replaygain_analysis.h"
  21 #include "FLAC/assert.h"
  22 #include "FLAC/file_decoder.h"
  23 #include "FLAC/metadata.h"
  24 #include <locale.h>
  25 #include <math.h>
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29 #if defined _MSC_VER || defined __MINGW32__
  30 #include <io.h> /* for chmod() */
  31 #endif
  32 #include <sys/stat.h> /* for stat(), maybe chmod() */
  33
  34 #ifdef local_min
  35 #undef local_min
  36 #endif
  37 #define local_min(a,b) ((a)<(b)?(a):(b))
  38
  39 #ifdef local_max
  40 #undef local_max
  41 #endif
  42 #define local_max(a,b) ((a)>(b)?(a):(b))
  43
  44 static const FLAC__byte *tag_title_gain_ = "REPLAYGAIN_TRACK_GAIN";
  45 static const FLAC__byte *tag_title_peak_ = "REPLAYGAIN_TRACK_PEAK";
  46 static const FLAC__byte *tag_album_gain_ = "REPLAYGAIN_ALBUM_GAIN";
  47 static const FLAC__byte *tag_album_peak_ = "REPLAYGAIN_ALBUM_PEAK";
  48 static const char *peak_format_ = "%s=%1.8f";
  49 static const char *gain_format_ = "%s=%+2.2f dB";
  50
  51 static double album_peak_, title_peak_;
  52
  53 const unsigned GRABBAG__REPLAYGAIN_MAX_TAG_SPACE_REQUIRED = 148;
  54 /*
  55         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 10 +
  56         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 12 +
  57         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 10 +
  58         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 12
  59 */
  60
  61
  62 static FLAC__bool get_file_stats_(const char *filename, struct stat *stats)
  63 {
  64         FLAC__ASSERT(0 != filename);
  65         FLAC__ASSERT(0 != stats);
  66         return (0 == stat(filename, stats));
  67 }
  68
  69 static void set_file_stats_(const char *filename, struct stat *stats)
  70 {
  71         FLAC__ASSERT(0 != filename);
  72         FLAC__ASSERT(0 != stats);
  73
  74         (void)chmod(filename, stats->st_mode);
  75 }
  76
  77 static FLAC__bool append_tag_(FLAC__StreamMetadata *block, const char *format, const FLAC__byte *name, float value)
  78 {
  79         char buffer[256];
  80         char *saved_locale;
  81         FLAC__StreamMetadata_VorbisComment_Entry entry;
  82
  83         FLAC__ASSERT(0 != block);
  84         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
  85         FLAC__ASSERT(0 != name);
  86         FLAC__ASSERT(0 != value);
  87
  88         buffer[sizeof(buffer)-1] = '\0';
  89         /*
  90          * We need to save the old locale and switch to "C" because the locale
  91          * influences the formatting of %f and we want it a certain way.
  92          */
  93         saved_locale = setlocale(LC_ALL, 0);
  94         setlocale(LC_ALL, "C");
  95 #if defined _MSC_VER || defined __MINGW32__
  96         _snprintf(buffer, sizeof(buffer)-1, format, name, value);
  97 #else
  98         snprintf(buffer, sizeof(buffer)-1, format, name, value);
  99 #endif
 100         setlocale(LC_ALL, saved_locale);
 101
 102         entry.entry = (FLAC__byte *)buffer;
 103         entry.length = strlen(buffer);
 104
 105         return FLAC__metadata_object_vorbiscomment_insert_comment(block, block->data.vorbis_comment.num_comments, entry, /*copy=*/true);
 106 }
 107
 108 FLAC__bool grabbag__replaygain_is_valid_sample_frequency(unsigned sample_frequency)
 109 {
 110         static const unsigned valid_sample_rates[] = {
 111                 8000,
 112                 11025,
 113                 12000,
 114                 16000,
 115                 22050,
 116                 24000,
 117                 32000,
 118                 44100,
 119                 48000
 120         };
 121         static const unsigned n_valid_sample_rates = sizeof(valid_sample_rates) / sizeof(valid_sample_rates[0]);
 122
 123         unsigned i;
 124
 125         for(i = 0; i < n_valid_sample_rates; i++)
 126                 if(sample_frequency == valid_sample_rates[i])
 127                         return true;
 128         return false;
 129 }
 130
 131 FLAC__bool grabbag__replaygain_init(unsigned sample_frequency)
 132 {
 133         title_peak_ = album_peak_ = 0.0;
 134         return InitGainAnalysis((long)sample_frequency) == INIT_GAIN_ANALYSIS_OK;
 135 }
 136
 137 FLAC__bool grabbag__replaygain_analyze(const FLAC__int32 * const input[], FLAC__bool is_stereo, unsigned bps, unsigned samples)
 138 {
 139         /* using a small buffer improves data locality; we'd like it to fit easily in the dcache */
 140         static Float_t lbuffer[2048], rbuffer[2048];
 141         static const unsigned nbuffer = sizeof(lbuffer) / sizeof(lbuffer[0]);
 142         FLAC__int32 block_peak = 0, s;
 143         unsigned i, j;
 144
 145         FLAC__ASSERT(bps >= 4 && bps <= FLAC__REFERENCE_CODEC_MAX_BITS_PER_SAMPLE);
 146         FLAC__ASSERT(FLAC__MIN_BITS_PER_SAMPLE == 4);
 147         /*
 148          * We use abs() on a FLAC__int32 which is undefined for the most negative value.
 149          * If the reference codec ever handles 32bps we will have to write a special
 150          * case here.
 151          */
 152         FLAC__ASSERT(FLAC__REFERENCE_CODEC_MAX_BITS_PER_SAMPLE < 32);
 153
 154         if(bps == 16) {
 155                 if(is_stereo) {
 156                         j = 0;
 157                         while(samples > 0) {
 158                                 const unsigned n = local_min(samples, nbuffer);
 159                                 for(i = 0; i < n; i++, j++) {
 160                                         s = input[0][j];
 161                                         lbuffer[i] = (Float_t)s;
 162                                         s = abs(s);
 163                                         block_peak = local_max(block_peak, s);
 164
 165                                         s = input[1][j];
 166                                         rbuffer[i] = (Float_t)s;
 167                                         s = abs(s);
 168                                         block_peak = local_max(block_peak, s);
 169                                 }
 170                                 samples -= n;
 171                                 if(AnalyzeSamples(lbuffer, rbuffer, n, 2) != GAIN_ANALYSIS_OK)
 172                                         return false;
 173                         }
 174                 }
 175                 else {
 176                         j = 0;
 177                         while(samples > 0) {
 178                                 const unsigned n = local_min(samples, nbuffer);
 179                                 for(i = 0; i < n; i++, j++) {
 180                                         s = input[0][j];
 181                                         lbuffer[i] = (Float_t)s;
 182                                         s = abs(s);
 183                                         block_peak = local_max(block_peak, s);
 184                                 }
 185                                 samples -= n;
 186                                 if(AnalyzeSamples(lbuffer, 0, n, 1) != GAIN_ANALYSIS_OK)
 187                                         return false;
 188                         }
 189                 }
 190         }
 191         else { /* bps must be < 32 according to above assertion */
 192                 const double scale = (
 193                         (bps > 16)?
 194                                 (double)1. / (double)(1u << (bps - 16)) :
 195                                 (double)(1u << (16 - bps))
 196                 );
 197
 198                 if(is_stereo) {
 199                         j = 0;
 200                         while(samples > 0) {
 201                                 const unsigned n = local_min(samples, nbuffer);
 202                                 for(i = 0; i < n; i++, j++) {
 203                                         s = input[0][j];
 204                                         lbuffer[i] = (Float_t)(scale * (double)s);
 205                                         s = abs(s);
 206                                         block_peak = local_max(block_peak, s);
 207
 208                                         s = input[1][j];
 209                                         rbuffer[i] = (Float_t)(scale * (double)s);
 210                                         s = abs(s);
 211                                         block_peak = local_max(block_peak, s);
 212                                 }
 213                                 samples -= n;
 214                                 if(AnalyzeSamples(lbuffer, rbuffer, n, 2) != GAIN_ANALYSIS_OK)
 215                                         return false;
 216                         }
 217                 }
 218                 else {
 219                         j = 0;
 220                         while(samples > 0) {
 221                                 const unsigned n = local_min(samples, nbuffer);
 222                                 for(i = 0; i < n; i++, j++) {
 223                                         s = input[0][j];
 224                                         lbuffer[i] = (Float_t)(scale * (double)s);
 225                                         s = abs(s);
 226                                         block_peak = local_max(block_peak, s);
 227                                 }
 228                                 samples -= n;
 229                                 if(AnalyzeSamples(lbuffer, 0, n, 1) != GAIN_ANALYSIS_OK)
 230                                         return false;
 231                         }
 232                 }
 233         }
 234
 235         {
 236                 const double peak_scale = (double)(1u << (bps - 1));
 237                 double peak = (double)block_peak / peak_scale;
 238                 if(peak > title_peak_)
 239                         title_peak_ = peak;
 240                 if(peak > album_peak_)
 241                         album_peak_ = peak;
 242         }
 243
 244         return true;
 245 }
 246
 247 void grabbag__replaygain_get_album(float *gain, float *peak)
 248 {
 249         *gain = (float)GetAlbumGain();
 250         *peak = (float)album_peak_;
 251         album_peak_ = 0.0;
 252 }
 253
 254 void grabbag__replaygain_get_title(float *gain, float *peak)
 255 {
 256         *gain = (float)GetTitleGain();
 257         *peak = (float)title_peak_;
 258         title_peak_ = 0.0;
 259 }
 260
 261
 262 typedef struct {
 263         unsigned channels;
 264         unsigned bits_per_sample;
 265         unsigned sample_rate;
 266         FLAC__bool error;
 267 } DecoderInstance;
 268
 269 static FLAC__StreamDecoderWriteStatus write_callback_(const FLAC__FileDecoder *decoder, const FLAC__Frame *frame, const FLAC__int32 * const buffer[], void *client_data)
 270 {
 271         DecoderInstance *instance = (DecoderInstance*)client_data;
 272         const unsigned bits_per_sample = frame->header.bits_per_sample;
 273         const unsigned channels = frame->header.channels;
 274         const unsigned sample_rate = frame->header.sample_rate;
 275         const unsigned samples = frame->header.blocksize;
 276
 277         (void)decoder;
 278
 279         if(
 280                 !instance->error &&
 281                 (channels == 2 || channels == 1) &&
 282                 bits_per_sample == instance->bits_per_sample &&
 283                 channels == instance->channels &&
 284                 sample_rate == instance->sample_rate
 285         ) {
 286                 instance->error = !grabbag__replaygain_analyze(buffer, channels==2, bits_per_sample, samples);
 287         }
 288         else {
 289                 instance->error = true;
 290         }
 291
 292         if(!instance->error)
 293                 return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
 294         else
 295                 return FLAC__STREAM_DECODER_WRITE_STATUS_ABORT;
 296 }
 297
 298 static void metadata_callback_(const FLAC__FileDecoder *decoder, const FLAC__StreamMetadata *metadata, void *client_data)
 299 {
 300         DecoderInstance *instance = (DecoderInstance*)client_data;
 301
 302         (void)decoder;
 303
 304         if(metadata->type == FLAC__METADATA_TYPE_STREAMINFO) {
 305                 instance->bits_per_sample = metadata->data.stream_info.bits_per_sample;
 306                 instance->channels = metadata->data.stream_info.channels;
 307                 instance->sample_rate = metadata->data.stream_info.sample_rate;
 308
 309                 if(instance->channels != 1 && instance->channels != 2) {
 310                         instance->error = true;
 311                         return;
 312                 }
 313
 314                 if(!grabbag__replaygain_is_valid_sample_frequency(instance->sample_rate)) {
 315                         instance->error = true;
 316                         return;
 317                 }
 318         }
 319 }
 320
 321 static void error_callback_(const FLAC__FileDecoder *decoder, FLAC__StreamDecoderErrorStatus status, void *client_data)
 322 {
 323         DecoderInstance *instance = (DecoderInstance*)client_data;
 324
 325         (void)decoder, (void)status;
 326
 327         instance->error = true;
 328 }
 329
 330 const char *grabbag__replaygain_analyze_file(const char *filename, float *title_gain, float *title_peak)
 331 {
 332         DecoderInstance instance;
 333         FLAC__FileDecoder *decoder = FLAC__file_decoder_new();
 334
 335         if(0 == decoder)
 336                 return "memory allocation error";
 337
 338         instance.error = false;
 339
 340         /* It does these three by default but lets be explicit: */
 341         FLAC__file_decoder_set_md5_checking(decoder, false);
 342         FLAC__file_decoder_set_metadata_ignore_all(decoder);
 343         FLAC__file_decoder_set_metadata_respond(decoder, FLAC__METADATA_TYPE_STREAMINFO);
 344
 345         FLAC__file_decoder_set_filename(decoder, filename);
 346         FLAC__file_decoder_set_write_callback(decoder, write_callback_);
 347         FLAC__file_decoder_set_metadata_callback(decoder, metadata_callback_);
 348         FLAC__file_decoder_set_error_callback(decoder, error_callback_);
 349         FLAC__file_decoder_set_client_data(decoder, &instance);
 350
 351         if(FLAC__file_decoder_init(decoder) != FLAC__FILE_DECODER_OK) {
 352                 FLAC__file_decoder_delete(decoder);
 353                 return "initializing decoder";
 354         }
 355
 356         if(!FLAC__file_decoder_process_until_end_of_file(decoder) || instance.error) {
 357                 FLAC__file_decoder_delete(decoder);
 358                 return "decoding file";
 359         }
 360
 361         FLAC__file_decoder_delete(decoder);
 362
 363         grabbag__replaygain_get_title(title_gain, title_peak);
 364
 365         return 0;
 366 }
 367
 368 const char *grabbag__replaygain_store_to_vorbiscomment(FLAC__StreamMetadata *block, float album_gain, float album_peak, float title_gain, float title_peak)
 369 {
 370         const char *error;
 371
 372         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_title(block, title_gain, title_peak)))
 373                 return error;
 374
 375         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_album(block, album_gain, album_peak)))
 376                 return error;
 377
 378         return 0;
 379 }
 380
 381 const char *grabbag__replaygain_store_to_vorbiscomment_album(FLAC__StreamMetadata *block, float album_gain, float album_peak)
 382 {
 383         FLAC__ASSERT(0 != block);
 384         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 385
 386         if(
 387                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)tag_album_gain_) < 0 ||
 388                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)tag_album_peak_) < 0
 389         )
 390                 return "memory allocation error";
 391
 392         if(
 393                 !append_tag_(block, peak_format_, tag_album_peak_, album_peak) ||
 394                 !append_tag_(block, gain_format_, tag_album_gain_, album_gain)
 395         )
 396                 return "memory allocation error";
 397
 398         return 0;
 399 }
 400
 401 const char *grabbag__replaygain_store_to_vorbiscomment_title(FLAC__StreamMetadata *block, float title_gain, float title_peak)
 402 {
 403         FLAC__ASSERT(0 != block);
 404         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 405
 406         if(
 407                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)tag_title_gain_) < 0 ||
 408                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)tag_title_peak_) < 0
 409         )
 410                 return "memory allocation error";
 411
 412         if(
 413                 !append_tag_(block, peak_format_, tag_title_peak_, title_peak) ||
 414                 !append_tag_(block, gain_format_, tag_title_gain_, title_gain)
 415         )
 416                 return "memory allocation error";
 417
 418         return 0;
 419 }
 420
 421 static const char *store_to_file_pre_(const char *filename, FLAC__Metadata_Chain **chain, FLAC__StreamMetadata **block)
 422 {
 423         FLAC__Metadata_Iterator *iterator;
 424         const char *error;
 425         FLAC__bool found_vc_block = false;
 426
 427         if(0 == (*chain = FLAC__metadata_chain_new()))
 428                 return "memory allocation error";
 429
 430         if(!FLAC__metadata_chain_read(*chain, filename)) {
 431                 error = FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(*chain)];
 432                 FLAC__metadata_chain_delete(*chain);
 433                 return error;
 434         }
 435
 436         if(0 == (iterator = FLAC__metadata_iterator_new())) {
 437                 FLAC__metadata_chain_delete(*chain);
 438                 return "memory allocation error";
 439         }
 440
 441         FLAC__metadata_iterator_init(iterator, *chain);
 442
 443         do {
 444                 *block = FLAC__metadata_iterator_get_block(iterator);
 445                 if((*block)->type == FLAC__METADATA_TYPE_VORBIS_COMMENT)
 446                         found_vc_block = true;
 447         } while(!found_vc_block && FLAC__metadata_iterator_next(iterator));
 448
 449         if(!found_vc_block) {
 450                 /* create a new block */
 451                 *block = FLAC__metadata_object_new(FLAC__METADATA_TYPE_VORBIS_COMMENT);
 452                 if(0 == *block) {
 453                         FLAC__metadata_chain_delete(*chain);
 454                         FLAC__metadata_iterator_delete(iterator);
 455                         return "memory allocation error";
 456                 }
 457                 while(FLAC__metadata_iterator_next(iterator))
 458                         ;
 459                 if(!FLAC__metadata_iterator_insert_block_after(iterator, *block)) {
 460                         error = FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(*chain)];
 461                         FLAC__metadata_chain_delete(*chain);
 462                         FLAC__metadata_iterator_delete(iterator);
 463                         return error;
 464                 }
 465                 /* iterator is left pointing to new block */
 466                 FLAC__ASSERT(FLAC__metadata_iterator_get_block(iterator) == *block);
 467         }
 468
 469         FLAC__metadata_iterator_delete(iterator);
 470
 471         FLAC__ASSERT(0 != *block);
 472         FLAC__ASSERT((*block)->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 473
 474         return 0;
 475 }
 476
 477 static const char *store_to_file_post_(const char *filename, FLAC__Metadata_Chain *chain, FLAC__bool preserve_modtime)
 478 {
 479         struct stat stats;
 480         const FLAC__bool have_stats = get_file_stats_(filename, &stats);
 481
 482         (void)grabbag__file_change_stats(filename, /*read_only=*/false);
 483
 484         FLAC__metadata_chain_sort_padding(chain);
 485         if(!FLAC__metadata_chain_write(chain, /*use_padding=*/true, preserve_modtime)) {
 486                 FLAC__metadata_chain_delete(chain);
 487                 return FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(chain)];
 488         }
 489
 490         FLAC__metadata_chain_delete(chain);
 491
 492         if(have_stats)
 493                 set_file_stats_(filename, &stats);
 494
 495         return 0;
 496 }
 497
 498 const char *grabbag__replaygain_store_to_file(const char *filename, float album_gain, float album_peak, float title_gain, float title_peak, FLAC__bool preserve_modtime)
 499 {
 500         FLAC__Metadata_Chain *chain;
 501         FLAC__StreamMetadata *block;
 502         const char *error;
 503
 504         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 505                 return error;
 506
 507         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment(block, album_gain, album_peak, title_gain, title_peak))) {
 508                 FLAC__metadata_chain_delete(chain);
 509                 return error;
 510         }
 511
 512         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 513                 return error;
 514
 515         return 0;
 516 }
 517
 518 const char *grabbag__replaygain_store_to_file_album(const char *filename, float album_gain, float album_peak, FLAC__bool preserve_modtime)
 519 {
 520         FLAC__Metadata_Chain *chain;
 521         FLAC__StreamMetadata *block;
 522         const char *error;
 523
 524         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 525                 return error;
 526
 527         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_album(block, album_gain, album_peak))) {
 528                 FLAC__metadata_chain_delete(chain);
 529                 return error;
 530         }
 531
 532         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 533                 return error;
 534
 535         return 0;
 536 }
 537
 538 const char *grabbag__replaygain_store_to_file_title(const char *filename, float title_gain, float title_peak, FLAC__bool preserve_modtime)
 539 {
 540         FLAC__Metadata_Chain *chain;
 541         FLAC__StreamMetadata *block;
 542         const char *error;
 543
 544         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 545                 return error;
 546
 547         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_title(block, title_gain, title_peak))) {
 548                 FLAC__metadata_chain_delete(chain);
 549                 return error;
 550         }
 551
 552         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 553                 return error;
 554
 555         return 0;
 556 }
 557
 558 static FLAC__bool parse_double_(const FLAC__StreamMetadata_VorbisComment_Entry *entry, double *val)
 559 {
 560         char s[32], *end;
 561         const char *p, *q;
 562         double v;
 563
 564         FLAC__ASSERT(0 != entry);
 565         FLAC__ASSERT(0 != val);
 566
 567         p = (const char *)entry->entry;
 568         q = strchr(p, '=');
 569         if(0 == q)
 570                 return false;
 571         q++;
 572         memset(s, 0, sizeof(s)-1);
 573         strncpy(s, q, local_min(sizeof(s)-1, entry->length - (q-p)));
 574
 575         v = strtod(s, &end);
 576         if(end == s)
 577                 return false;
 578
 579         *val = v;
 580         return true;
 581 }
 582
 583 FLAC__bool grabbag__replaygain_load_from_vorbiscomment(const FLAC__StreamMetadata *block, FLAC__bool album_mode, double *gain, double *peak)
 584 {
 585         int gain_offset, peak_offset;
 586
 587         FLAC__ASSERT(0 != block);
 588         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 589
 590         if(0 > (gain_offset = FLAC__metadata_object_vorbiscomment_find_entry_from(block, /*offset=*/0, (const char *)(album_mode? tag_album_gain_ : tag_title_gain_))))
 591                 return false;
 592         if(0 > (peak_offset = FLAC__metadata_object_vorbiscomment_find_entry_from(block, /*offset=*/0, (const char *)(album_mode? tag_album_peak_ : tag_title_peak_))))
 593                 return false;
 594
 595         if(!parse_double_(block->data.vorbis_comment.comments + gain_offset, gain))
 596                 return false;
 597         if(!parse_double_(block->data.vorbis_comment.comments + peak_offset, peak))
 598                 return false;
 599
 600         return true;
 601 }
 602
 603 double grabbag__replaygain_compute_scale_factor(double peak, double gain, double preamp, FLAC__bool prevent_clipping)
 604 {
 605         double scale;
 606         FLAC__ASSERT(peak >= 0.0);
 607         gain += preamp;
 608         scale = (float) pow(10.0, gain * 0.05);
 609         if(prevent_clipping && peak > 0.0) {
 610                 const double max_scale = (float)(1.0 / peak);
 611                 if(scale > max_scale)
 612                         scale = max_scale;
 613         }
 614         return scale;
 615 }