src/share/grabbag/replaygain.c

   1 /* grabbag - Convenience lib for various routines common to several tools
   2  * Copyright (C) 2002,2003,2004,2005  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 char *peak_format_ = "%s=%1.8f";
  45 static const char *gain_format_ = "%s=%+2.2f dB";
  46
  47 static double album_peak_, title_peak_;
  48
  49 const unsigned GRABBAG__REPLAYGAIN_MAX_TAG_SPACE_REQUIRED = 148;
  50 /*
  51         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 10 +
  52         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 12 +
  53         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 10 +
  54         FLAC__STREAM_METADATA_VORBIS_COMMENT_ENTRY_LENGTH_LEN/8 + 21 + 1 + 12
  55 */
  56
  57 const FLAC__byte * const GRABBAG__REPLAYGAIN_TAG_TITLE_GAIN = (const FLAC__byte * const)"REPLAYGAIN_TRACK_GAIN";
  58 const FLAC__byte * const GRABBAG__REPLAYGAIN_TAG_TITLE_PEAK = (const FLAC__byte * const)"REPLAYGAIN_TRACK_PEAK";
  59 const FLAC__byte * const GRABBAG__REPLAYGAIN_TAG_ALBUM_GAIN = (const FLAC__byte * const)"REPLAYGAIN_ALBUM_GAIN";
  60 const FLAC__byte * const GRABBAG__REPLAYGAIN_TAG_ALBUM_PEAK = (const FLAC__byte * const)"REPLAYGAIN_ALBUM_PEAK";
  61
  62
  63 static FLAC__bool get_file_stats_(const char *filename, struct stat *stats)
  64 {
  65         FLAC__ASSERT(0 != filename);
  66         FLAC__ASSERT(0 != stats);
  67         return (0 == stat(filename, stats));
  68 }
  69
  70 static void set_file_stats_(const char *filename, struct stat *stats)
  71 {
  72         FLAC__ASSERT(0 != filename);
  73         FLAC__ASSERT(0 != stats);
  74
  75         (void)chmod(filename, stats->st_mode);
  76 }
  77
  78 static FLAC__bool append_tag_(FLAC__StreamMetadata *block, const char *format, const FLAC__byte *name, float value)
  79 {
  80         char buffer[256];
  81         char *saved_locale;
  82         FLAC__StreamMetadata_VorbisComment_Entry entry;
  83
  84         FLAC__ASSERT(0 != block);
  85         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
  86         FLAC__ASSERT(0 != name);
  87         FLAC__ASSERT(0 != value);
  88
  89         buffer[sizeof(buffer)-1] = '\0';
  90         /*
  91          * We need to save the old locale and switch to "C" because the locale
  92          * influences the formatting of %f and we want it a certain way.
  93          */
  94         saved_locale = setlocale(LC_ALL, 0);
  95         setlocale(LC_ALL, "C");
  96 #if defined _MSC_VER || defined __MINGW32__
  97         _snprintf(buffer, sizeof(buffer)-1, format, name, value);
  98 #else
  99         snprintf(buffer, sizeof(buffer)-1, format, name, value);
 100 #endif
 101         setlocale(LC_ALL, saved_locale);
 102
 103         entry.entry = (FLAC__byte *)buffer;
 104         entry.length = strlen(buffer);
 105
 106         return FLAC__metadata_object_vorbiscomment_append_comment(block, entry, /*copy=*/true);
 107 }
 108
 109 FLAC__bool grabbag__replaygain_is_valid_sample_frequency(unsigned sample_frequency)
 110 {
 111         static const unsigned valid_sample_rates[] = {
 112                 8000,
 113                 11025,
 114                 12000,
 115                 16000,
 116                 22050,
 117                 24000,
 118                 32000,
 119                 44100,
 120                 48000
 121         };
 122         static const unsigned n_valid_sample_rates = sizeof(valid_sample_rates) / sizeof(valid_sample_rates[0]);
 123
 124         unsigned i;
 125
 126         for(i = 0; i < n_valid_sample_rates; i++)
 127                 if(sample_frequency == valid_sample_rates[i])
 128                         return true;
 129         return false;
 130 }
 131
 132 FLAC__bool grabbag__replaygain_init(unsigned sample_frequency)
 133 {
 134         title_peak_ = album_peak_ = 0.0;
 135         return InitGainAnalysis((long)sample_frequency) == INIT_GAIN_ANALYSIS_OK;
 136 }
 137
 138 FLAC__bool grabbag__replaygain_analyze(const FLAC__int32 * const input[], FLAC__bool is_stereo, unsigned bps, unsigned samples)
 139 {
 140         /* using a small buffer improves data locality; we'd like it to fit easily in the dcache */
 141         static Float_t lbuffer[2048], rbuffer[2048];
 142         static const unsigned nbuffer = sizeof(lbuffer) / sizeof(lbuffer[0]);
 143         FLAC__int32 block_peak = 0, s;
 144         unsigned i, j;
 145
 146         FLAC__ASSERT(bps >= 4 && bps <= FLAC__REFERENCE_CODEC_MAX_BITS_PER_SAMPLE);
 147         FLAC__ASSERT(FLAC__MIN_BITS_PER_SAMPLE == 4);
 148         /*
 149          * We use abs() on a FLAC__int32 which is undefined for the most negative value.
 150          * If the reference codec ever handles 32bps we will have to write a special
 151          * case here.
 152          */
 153         FLAC__ASSERT(FLAC__REFERENCE_CODEC_MAX_BITS_PER_SAMPLE < 32);
 154
 155         if(bps == 16) {
 156                 if(is_stereo) {
 157                         j = 0;
 158                         while(samples > 0) {
 159                                 const unsigned n = local_min(samples, nbuffer);
 160                                 for(i = 0; i < n; i++, j++) {
 161                                         s = input[0][j];
 162                                         lbuffer[i] = (Float_t)s;
 163                                         s = abs(s);
 164                                         block_peak = local_max(block_peak, s);
 165
 166                                         s = input[1][j];
 167                                         rbuffer[i] = (Float_t)s;
 168                                         s = abs(s);
 169                                         block_peak = local_max(block_peak, s);
 170                                 }
 171                                 samples -= n;
 172                                 if(AnalyzeSamples(lbuffer, rbuffer, n, 2) != GAIN_ANALYSIS_OK)
 173                                         return false;
 174                         }
 175                 }
 176                 else {
 177                         j = 0;
 178                         while(samples > 0) {
 179                                 const unsigned n = local_min(samples, nbuffer);
 180                                 for(i = 0; i < n; i++, j++) {
 181                                         s = input[0][j];
 182                                         lbuffer[i] = (Float_t)s;
 183                                         s = abs(s);
 184                                         block_peak = local_max(block_peak, s);
 185                                 }
 186                                 samples -= n;
 187                                 if(AnalyzeSamples(lbuffer, 0, n, 1) != GAIN_ANALYSIS_OK)
 188                                         return false;
 189                         }
 190                 }
 191         }
 192         else { /* bps must be < 32 according to above assertion */
 193                 const double scale = (
 194                         (bps > 16)?
 195                                 (double)1. / (double)(1u << (bps - 16)) :
 196                                 (double)(1u << (16 - bps))
 197                 );
 198
 199                 if(is_stereo) {
 200                         j = 0;
 201                         while(samples > 0) {
 202                                 const unsigned n = local_min(samples, nbuffer);
 203                                 for(i = 0; i < n; i++, j++) {
 204                                         s = input[0][j];
 205                                         lbuffer[i] = (Float_t)(scale * (double)s);
 206                                         s = abs(s);
 207                                         block_peak = local_max(block_peak, s);
 208
 209                                         s = input[1][j];
 210                                         rbuffer[i] = (Float_t)(scale * (double)s);
 211                                         s = abs(s);
 212                                         block_peak = local_max(block_peak, s);
 213                                 }
 214                                 samples -= n;
 215                                 if(AnalyzeSamples(lbuffer, rbuffer, n, 2) != GAIN_ANALYSIS_OK)
 216                                         return false;
 217                         }
 218                 }
 219                 else {
 220                         j = 0;
 221                         while(samples > 0) {
 222                                 const unsigned n = local_min(samples, nbuffer);
 223                                 for(i = 0; i < n; i++, j++) {
 224                                         s = input[0][j];
 225                                         lbuffer[i] = (Float_t)(scale * (double)s);
 226                                         s = abs(s);
 227                                         block_peak = local_max(block_peak, s);
 228                                 }
 229                                 samples -= n;
 230                                 if(AnalyzeSamples(lbuffer, 0, n, 1) != GAIN_ANALYSIS_OK)
 231                                         return false;
 232                         }
 233                 }
 234         }
 235
 236         {
 237                 const double peak_scale = (double)(1u << (bps - 1));
 238                 double peak = (double)block_peak / peak_scale;
 239                 if(peak > title_peak_)
 240                         title_peak_ = peak;
 241                 if(peak > album_peak_)
 242                         album_peak_ = peak;
 243         }
 244
 245         return true;
 246 }
 247
 248 void grabbag__replaygain_get_album(float *gain, float *peak)
 249 {
 250         *gain = (float)GetAlbumGain();
 251         *peak = (float)album_peak_;
 252         album_peak_ = 0.0;
 253 }
 254
 255 void grabbag__replaygain_get_title(float *gain, float *peak)
 256 {
 257         *gain = (float)GetTitleGain();
 258         *peak = (float)title_peak_;
 259         title_peak_ = 0.0;
 260 }
 261
 262
 263 typedef struct {
 264         unsigned channels;
 265         unsigned bits_per_sample;
 266         unsigned sample_rate;
 267         FLAC__bool error;
 268 } DecoderInstance;
 269
 270 static FLAC__StreamDecoderWriteStatus write_callback_(const FLAC__FileDecoder *decoder, const FLAC__Frame *frame, const FLAC__int32 * const buffer[], void *client_data)
 271 {
 272         DecoderInstance *instance = (DecoderInstance*)client_data;
 273         const unsigned bits_per_sample = frame->header.bits_per_sample;
 274         const unsigned channels = frame->header.channels;
 275         const unsigned sample_rate = frame->header.sample_rate;
 276         const unsigned samples = frame->header.blocksize;
 277
 278         (void)decoder;
 279
 280         if(
 281                 !instance->error &&
 282                 (channels == 2 || channels == 1) &&
 283                 bits_per_sample == instance->bits_per_sample &&
 284                 channels == instance->channels &&
 285                 sample_rate == instance->sample_rate
 286         ) {
 287                 instance->error = !grabbag__replaygain_analyze(buffer, channels==2, bits_per_sample, samples);
 288         }
 289         else {
 290                 instance->error = true;
 291         }
 292
 293         if(!instance->error)
 294                 return FLAC__STREAM_DECODER_WRITE_STATUS_CONTINUE;
 295         else
 296                 return FLAC__STREAM_DECODER_WRITE_STATUS_ABORT;
 297 }
 298
 299 static void metadata_callback_(const FLAC__FileDecoder *decoder, const FLAC__StreamMetadata *metadata, void *client_data)
 300 {
 301         DecoderInstance *instance = (DecoderInstance*)client_data;
 302
 303         (void)decoder;
 304
 305         if(metadata->type == FLAC__METADATA_TYPE_STREAMINFO) {
 306                 instance->bits_per_sample = metadata->data.stream_info.bits_per_sample;
 307                 instance->channels = metadata->data.stream_info.channels;
 308                 instance->sample_rate = metadata->data.stream_info.sample_rate;
 309
 310                 if(instance->channels != 1 && instance->channels != 2) {
 311                         instance->error = true;
 312                         return;
 313                 }
 314
 315                 if(!grabbag__replaygain_is_valid_sample_frequency(instance->sample_rate)) {
 316                         instance->error = true;
 317                         return;
 318                 }
 319         }
 320 }
 321
 322 static void error_callback_(const FLAC__FileDecoder *decoder, FLAC__StreamDecoderErrorStatus status, void *client_data)
 323 {
 324         DecoderInstance *instance = (DecoderInstance*)client_data;
 325
 326         (void)decoder, (void)status;
 327
 328         instance->error = true;
 329 }
 330
 331 const char *grabbag__replaygain_analyze_file(const char *filename, float *title_gain, float *title_peak)
 332 {
 333         DecoderInstance instance;
 334         FLAC__FileDecoder *decoder = FLAC__file_decoder_new();
 335
 336         if(0 == decoder)
 337                 return "memory allocation error";
 338
 339         instance.error = false;
 340
 341         /* It does these three by default but lets be explicit: */
 342         FLAC__file_decoder_set_md5_checking(decoder, false);
 343         FLAC__file_decoder_set_metadata_ignore_all(decoder);
 344         FLAC__file_decoder_set_metadata_respond(decoder, FLAC__METADATA_TYPE_STREAMINFO);
 345
 346         FLAC__file_decoder_set_filename(decoder, filename);
 347         FLAC__file_decoder_set_write_callback(decoder, write_callback_);
 348         FLAC__file_decoder_set_metadata_callback(decoder, metadata_callback_);
 349         FLAC__file_decoder_set_error_callback(decoder, error_callback_);
 350         FLAC__file_decoder_set_client_data(decoder, &instance);
 351
 352         if(FLAC__file_decoder_init(decoder) != FLAC__FILE_DECODER_OK) {
 353                 FLAC__file_decoder_delete(decoder);
 354                 return "initializing decoder";
 355         }
 356
 357         if(!FLAC__file_decoder_process_until_end_of_file(decoder) || instance.error) {
 358                 FLAC__file_decoder_delete(decoder);
 359                 return "decoding file";
 360         }
 361
 362         FLAC__file_decoder_delete(decoder);
 363
 364         grabbag__replaygain_get_title(title_gain, title_peak);
 365
 366         return 0;
 367 }
 368
 369 const char *grabbag__replaygain_store_to_vorbiscomment(FLAC__StreamMetadata *block, float album_gain, float album_peak, float title_gain, float title_peak)
 370 {
 371         const char *error;
 372
 373         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_title(block, title_gain, title_peak)))
 374                 return error;
 375
 376         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_album(block, album_gain, album_peak)))
 377                 return error;
 378
 379         return 0;
 380 }
 381
 382 const char *grabbag__replaygain_store_to_vorbiscomment_album(FLAC__StreamMetadata *block, float album_gain, float album_peak)
 383 {
 384         FLAC__ASSERT(0 != block);
 385         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 386
 387         if(
 388                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)GRABBAG__REPLAYGAIN_TAG_ALBUM_GAIN) < 0 ||
 389                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)GRABBAG__REPLAYGAIN_TAG_ALBUM_PEAK) < 0
 390         )
 391                 return "memory allocation error";
 392
 393         if(
 394                 !append_tag_(block, peak_format_, GRABBAG__REPLAYGAIN_TAG_ALBUM_PEAK, album_peak) ||
 395                 !append_tag_(block, gain_format_, GRABBAG__REPLAYGAIN_TAG_ALBUM_GAIN, album_gain)
 396         )
 397                 return "memory allocation error";
 398
 399         return 0;
 400 }
 401
 402 const char *grabbag__replaygain_store_to_vorbiscomment_title(FLAC__StreamMetadata *block, float title_gain, float title_peak)
 403 {
 404         FLAC__ASSERT(0 != block);
 405         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 406
 407         if(
 408                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)GRABBAG__REPLAYGAIN_TAG_TITLE_GAIN) < 0 ||
 409                 FLAC__metadata_object_vorbiscomment_remove_entries_matching(block, (const char *)GRABBAG__REPLAYGAIN_TAG_TITLE_PEAK) < 0
 410         )
 411                 return "memory allocation error";
 412
 413         if(
 414                 !append_tag_(block, peak_format_, GRABBAG__REPLAYGAIN_TAG_TITLE_PEAK, title_peak) ||
 415                 !append_tag_(block, gain_format_, GRABBAG__REPLAYGAIN_TAG_TITLE_GAIN, title_gain)
 416         )
 417                 return "memory allocation error";
 418
 419         return 0;
 420 }
 421
 422 static const char *store_to_file_pre_(const char *filename, FLAC__Metadata_Chain **chain, FLAC__StreamMetadata **block)
 423 {
 424         FLAC__Metadata_Iterator *iterator;
 425         const char *error;
 426         FLAC__bool found_vc_block = false;
 427
 428         if(0 == (*chain = FLAC__metadata_chain_new()))
 429                 return "memory allocation error";
 430
 431         if(!FLAC__metadata_chain_read(*chain, filename)) {
 432                 error = FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(*chain)];
 433                 FLAC__metadata_chain_delete(*chain);
 434                 return error;
 435         }
 436
 437         if(0 == (iterator = FLAC__metadata_iterator_new())) {
 438                 FLAC__metadata_chain_delete(*chain);
 439                 return "memory allocation error";
 440         }
 441
 442         FLAC__metadata_iterator_init(iterator, *chain);
 443
 444         do {
 445                 *block = FLAC__metadata_iterator_get_block(iterator);
 446                 if((*block)->type == FLAC__METADATA_TYPE_VORBIS_COMMENT)
 447                         found_vc_block = true;
 448         } while(!found_vc_block && FLAC__metadata_iterator_next(iterator));
 449
 450         if(!found_vc_block) {
 451                 /* create a new block */
 452                 *block = FLAC__metadata_object_new(FLAC__METADATA_TYPE_VORBIS_COMMENT);
 453                 if(0 == *block) {
 454                         FLAC__metadata_chain_delete(*chain);
 455                         FLAC__metadata_iterator_delete(iterator);
 456                         return "memory allocation error";
 457                 }
 458                 while(FLAC__metadata_iterator_next(iterator))
 459                         ;
 460                 if(!FLAC__metadata_iterator_insert_block_after(iterator, *block)) {
 461                         error = FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(*chain)];
 462                         FLAC__metadata_chain_delete(*chain);
 463                         FLAC__metadata_iterator_delete(iterator);
 464                         return error;
 465                 }
 466                 /* iterator is left pointing to new block */
 467                 FLAC__ASSERT(FLAC__metadata_iterator_get_block(iterator) == *block);
 468         }
 469
 470         FLAC__metadata_iterator_delete(iterator);
 471
 472         FLAC__ASSERT(0 != *block);
 473         FLAC__ASSERT((*block)->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 474
 475         return 0;
 476 }
 477
 478 static const char *store_to_file_post_(const char *filename, FLAC__Metadata_Chain *chain, FLAC__bool preserve_modtime)
 479 {
 480         struct stat stats;
 481         const FLAC__bool have_stats = get_file_stats_(filename, &stats);
 482
 483         (void)grabbag__file_change_stats(filename, /*read_only=*/false);
 484
 485         FLAC__metadata_chain_sort_padding(chain);
 486         if(!FLAC__metadata_chain_write(chain, /*use_padding=*/true, preserve_modtime)) {
 487                 FLAC__metadata_chain_delete(chain);
 488                 return FLAC__Metadata_ChainStatusString[FLAC__metadata_chain_status(chain)];
 489         }
 490
 491         FLAC__metadata_chain_delete(chain);
 492
 493         if(have_stats)
 494                 set_file_stats_(filename, &stats);
 495
 496         return 0;
 497 }
 498
 499 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)
 500 {
 501         FLAC__Metadata_Chain *chain;
 502         FLAC__StreamMetadata *block;
 503         const char *error;
 504
 505         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 506                 return error;
 507
 508         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment(block, album_gain, album_peak, title_gain, title_peak))) {
 509                 FLAC__metadata_chain_delete(chain);
 510                 return error;
 511         }
 512
 513         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 514                 return error;
 515
 516         return 0;
 517 }
 518
 519 const char *grabbag__replaygain_store_to_file_album(const char *filename, float album_gain, float album_peak, FLAC__bool preserve_modtime)
 520 {
 521         FLAC__Metadata_Chain *chain;
 522         FLAC__StreamMetadata *block;
 523         const char *error;
 524
 525         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 526                 return error;
 527
 528         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_album(block, album_gain, album_peak))) {
 529                 FLAC__metadata_chain_delete(chain);
 530                 return error;
 531         }
 532
 533         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 534                 return error;
 535
 536         return 0;
 537 }
 538
 539 const char *grabbag__replaygain_store_to_file_title(const char *filename, float title_gain, float title_peak, FLAC__bool preserve_modtime)
 540 {
 541         FLAC__Metadata_Chain *chain;
 542         FLAC__StreamMetadata *block;
 543         const char *error;
 544
 545         if(0 != (error = store_to_file_pre_(filename, &chain, &block)))
 546                 return error;
 547
 548         if(0 != (error = grabbag__replaygain_store_to_vorbiscomment_title(block, title_gain, title_peak))) {
 549                 FLAC__metadata_chain_delete(chain);
 550                 return error;
 551         }
 552
 553         if(0 != (error = store_to_file_post_(filename, chain, preserve_modtime)))
 554                 return error;
 555
 556         return 0;
 557 }
 558
 559 static FLAC__bool parse_double_(const FLAC__StreamMetadata_VorbisComment_Entry *entry, double *val)
 560 {
 561         char s[32], *end;
 562         const char *p, *q;
 563         double v;
 564
 565         FLAC__ASSERT(0 != entry);
 566         FLAC__ASSERT(0 != val);
 567
 568         p = (const char *)entry->entry;
 569         q = strchr(p, '=');
 570         if(0 == q)
 571                 return false;
 572         q++;
 573         memset(s, 0, sizeof(s)-1);
 574         strncpy(s, q, local_min(sizeof(s)-1, entry->length - (q-p)));
 575
 576         v = strtod(s, &end);
 577         if(end == s)
 578                 return false;
 579
 580         *val = v;
 581         return true;
 582 }
 583
 584 FLAC__bool grabbag__replaygain_load_from_vorbiscomment(const FLAC__StreamMetadata *block, FLAC__bool album_mode, double *gain, double *peak)
 585 {
 586         int gain_offset, peak_offset;
 587
 588         FLAC__ASSERT(0 != block);
 589         FLAC__ASSERT(block->type == FLAC__METADATA_TYPE_VORBIS_COMMENT);
 590
 591         if(0 > (gain_offset = FLAC__metadata_object_vorbiscomment_find_entry_from(block, /*offset=*/0, (const char *)(album_mode? GRABBAG__REPLAYGAIN_TAG_ALBUM_GAIN : GRABBAG__REPLAYGAIN_TAG_TITLE_GAIN))))
 592                 return false;
 593         if(0 > (peak_offset = FLAC__metadata_object_vorbiscomment_find_entry_from(block, /*offset=*/0, (const char *)(album_mode? GRABBAG__REPLAYGAIN_TAG_ALBUM_PEAK : GRABBAG__REPLAYGAIN_TAG_TITLE_PEAK))))
 594                 return false;
 595
 596         if(!parse_double_(block->data.vorbis_comment.comments + gain_offset, gain))
 597                 return false;
 598         if(!parse_double_(block->data.vorbis_comment.comments + peak_offset, peak))
 599                 return false;
 600
 601         return true;
 602 }
 603
 604 double grabbag__replaygain_compute_scale_factor(double peak, double gain, double preamp, FLAC__bool prevent_clipping)
 605 {
 606         double scale;
 607         FLAC__ASSERT(peak >= 0.0);
 608         gain += preamp;
 609         scale = (float) pow(10.0, gain * 0.05);
 610         if(prevent_clipping && peak > 0.0) {
 611                 const double max_scale = (float)(1.0 / peak);
 612                 if(scale > max_scale)
 613                         scale = max_scale;
 614         }
 615         return scale;
 616 }