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LibAudio: Use symbolic constants for MP3 frame and granule size
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@kleinesfilmroellchen @gmta
kleinesfilmroellchen authored and gmta committed Mar 13, 2023
1 parent 264cc76 commit 4420e48
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Showing 2 changed files with 24 additions and 19 deletions.
37 changes: 19 additions & 18 deletions Userland/Libraries/LibAudio/MP3Loader.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
*/

#include "MP3Loader.h"
#include "LibAudio/MP3Types.h"
#include "MP3HuffmanTables.h"
#include "MP3Tables.h"
#include <AK/FixedArray.h>
Expand Down Expand Up @@ -93,7 +94,7 @@ ErrorOr<Vector<FixedArray<Sample>>, LoaderError> MP3LoaderPlugin::load_chunks(si
int samples_to_read = samples_to_read_from_input;
Vector<FixedArray<Sample>> frames;
while (samples_to_read > 0) {
FixedArray<Sample> samples = LOADER_TRY(FixedArray<Sample>::create(1152));
FixedArray<Sample> samples = LOADER_TRY(FixedArray<Sample>::create(MP3::frame_size));

if (!m_current_frame.has_value()) {
auto maybe_frame = read_next_frame();
Expand All @@ -109,16 +110,16 @@ ErrorOr<Vector<FixedArray<Sample>>, LoaderError> MP3LoaderPlugin::load_chunks(si
}

bool const is_stereo = m_current_frame->header.channel_count() == 2;
auto current_frame_read = 0;
for (; current_frame_read < 576; current_frame_read++) {
size_t current_frame_read = 0;
for (; current_frame_read < MP3::granule_size; current_frame_read++) {
auto const left_sample = m_current_frame->channels[0].granules[0].pcm[current_frame_read / 32][current_frame_read % 32];
auto const right_sample = is_stereo ? m_current_frame->channels[1].granules[0].pcm[current_frame_read / 32][current_frame_read % 32] : left_sample;
samples[current_frame_read] = Sample { left_sample, right_sample };
samples_to_read--;
}
for (; current_frame_read < 1152; current_frame_read++) {
auto const left_sample = m_current_frame->channels[0].granules[1].pcm[(current_frame_read - 576) / 32][(current_frame_read - 576) % 32];
auto const right_sample = is_stereo ? m_current_frame->channels[1].granules[1].pcm[(current_frame_read - 576) / 32][(current_frame_read - 576) % 32] : left_sample;
for (; current_frame_read < MP3::frame_size; current_frame_read++) {
auto const left_sample = m_current_frame->channels[0].granules[1].pcm[(current_frame_read - MP3::granule_size) / 32][(current_frame_read - MP3::granule_size) % 32];
auto const right_sample = is_stereo ? m_current_frame->channels[1].granules[1].pcm[(current_frame_read - MP3::granule_size) / 32][(current_frame_read - MP3::granule_size) % 32] : left_sample;
samples[current_frame_read] = Sample { left_sample, right_sample };
samples_to_read--;
}
Expand Down Expand Up @@ -146,7 +147,7 @@ MaybeLoaderError MP3LoaderPlugin::build_seek_table()
continue;
}
frame_count++;
sample_count += 1152;
sample_count += MP3::frame_size;

if (frame_count % 10 == 0)
m_seek_table.append({ frame_pos, sample_count });
Expand Down Expand Up @@ -269,7 +270,7 @@ ErrorOr<MP3::MP3Frame, LoaderError> MP3LoaderPlugin::read_frame_data(MP3::Header
for (size_t channel_index = 0; channel_index < header.channel_count(); channel_index++) {
auto& granule = frame.channels[channel_index].granules[granule_index];

for (size_t i = 0; i < 576; i += 18) {
for (size_t i = 0; i < MP3::granule_size; i += 18) {
MP3::BlockType block_type = granule.block_type;
if (i < 36 && granule.mixed_block_flag) {
// ISO/IEC 11172-3: if mixed_block_flag is set, the lowest two subbands are transformed with normal window.
Expand Down Expand Up @@ -357,9 +358,9 @@ MaybeLoaderError MP3LoaderPlugin::read_side_information(MP3::MP3Frame& frame)
}

// From ISO/IEC 11172-3 (2.4.3.4.7.1)
Array<float, 576> MP3LoaderPlugin::calculate_frame_exponents(MP3::MP3Frame const& frame, size_t granule_index, size_t channel_index)
Array<float, MP3::granule_size> MP3LoaderPlugin::calculate_frame_exponents(MP3::MP3Frame const& frame, size_t granule_index, size_t channel_index)
{
Array<float, 576> exponents;
Array<float, MP3::granule_size> exponents;

auto fill_band = [&exponents](float exponent, size_t start, size_t end) {
for (size_t j = start; j <= end; j++) {
Expand Down Expand Up @@ -396,7 +397,7 @@ Array<float, 576> MP3LoaderPlugin::calculate_frame_exponents(MP3::MP3Frame const
float const gain1 = (gain - 8 * granule.sub_block_gain[1]) / 4.0;
float const gain2 = (gain - 8 * granule.sub_block_gain[2]) / 4.0;

while (sample_count < 576 && band_index < scale_factor_bands.size()) {
while (sample_count < MP3::granule_size && band_index < scale_factor_bands.size()) {
float const exponent0 = gain0 - (scale_factor_multiplier * channel.scale_factors[band_index + 0]);
float const exponent1 = gain1 - (scale_factor_multiplier * channel.scale_factors[band_index + 1]);
float const exponent2 = gain2 - (scale_factor_multiplier * channel.scale_factors[band_index + 2]);
Expand All @@ -411,7 +412,7 @@ Array<float, 576> MP3LoaderPlugin::calculate_frame_exponents(MP3::MP3Frame const
band_index += 3;
}

while (sample_count < 576)
while (sample_count < MP3::granule_size)
exponents[sample_count++] = 0;
}
return exponents;
Expand Down Expand Up @@ -496,7 +497,7 @@ MaybeLoaderError MP3LoaderPlugin::read_huffman_data(MP3::MP3Frame& frame, BigEnd

bool const is_short_granule = granule.window_switching_flag && granule.block_type == MP3::BlockType::Short;
size_t const region1_start = is_short_granule ? 36 : scale_factor_bands[scale_factor_band_index1].start;
size_t const region2_start = is_short_granule ? 576 : scale_factor_bands[scale_factor_band_index2].start;
size_t const region2_start = is_short_granule ? MP3::granule_size : scale_factor_bands[scale_factor_band_index2].start;

auto requantize = [](int const sample, float const exponent) -> float {
int const sign = sample < 0 ? -1 : 1;
Expand Down Expand Up @@ -560,7 +561,7 @@ MaybeLoaderError MP3LoaderPlugin::read_huffman_data(MP3::MP3Frame& frame, BigEnd
// until we've exhausted the granule's bits. We know the size of
// the granule from part2_3_length, which is the number of bits
// used for scaleactors and huffman data (in the granule).
while (granule_bits_read < granule.part_2_3_length && count <= 576 - 4) {
while (granule_bits_read < granule.part_2_3_length && count <= MP3::granule_size - 4) {
auto const entry = MP3::Tables::Huffman::huffman_decode(reservoir, count1table, granule.part_2_3_length - granule_bits_read);
granule_bits_read += entry.bits_read;
if (!entry.code.has_value())
Expand Down Expand Up @@ -619,7 +620,7 @@ MaybeLoaderError MP3LoaderPlugin::read_huffman_data(MP3::MP3Frame& frame, BigEnd

void MP3LoaderPlugin::reorder_samples(MP3::Granule& granule, u32 sample_rate)
{
float tmp[576] = {};
float tmp[MP3::granule_size] = {};
size_t band_index = 0;
size_t subband_index = 0;

Expand All @@ -635,7 +636,7 @@ void MP3LoaderPlugin::reorder_samples(MP3::Granule& granule, u32 sample_rate)
}
}

while (subband_index < 576 && band_index <= 36) {
while (subband_index < MP3::granule_size && band_index <= 36) {
for (size_t frequency_line_index = 0; frequency_line_index < scale_factor_bands[band_index].width; frequency_line_index++) {
tmp[subband_index++] = granule.samples[scale_factor_bands[band_index + 0].start + frequency_line_index];
tmp[subband_index++] = granule.samples[scale_factor_bands[band_index + 1].start + frequency_line_index];
Expand All @@ -644,7 +645,7 @@ void MP3LoaderPlugin::reorder_samples(MP3::Granule& granule, u32 sample_rate)
band_index += 3;
}

for (size_t i = 0; i < 576; i++)
for (size_t i = 0; i < MP3::granule_size; i++)
granule.samples[i] = tmp[i];
}

Expand Down Expand Up @@ -738,7 +739,7 @@ void MP3LoaderPlugin::process_stereo(MP3::MP3Frame& frame, size_t granule_index)
}
}

void MP3LoaderPlugin::transform_samples_to_time(Array<float, 576> const& input, size_t input_offset, Array<float, 36>& output, MP3::BlockType block_type)
void MP3LoaderPlugin::transform_samples_to_time(Array<float, MP3::granule_size> const& input, size_t input_offset, Array<float, 36>& output, MP3::BlockType block_type)
{
if (block_type == MP3::BlockType::Short) {
size_t const N = 12;
Expand Down
6 changes: 5 additions & 1 deletion Userland/Libraries/LibAudio/MP3Types.h
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Original file line number Diff line number Diff line change
Expand Up @@ -12,6 +12,10 @@

namespace Audio::MP3 {

constexpr size_t const frame_size = 1152;
// 576 samples.
constexpr size_t const granule_size = frame_size / 2;

enum class Mode {
Stereo = 0,
JointStereo = 1,
Expand Down Expand Up @@ -61,7 +65,7 @@ struct Header {
};

struct Granule {
Array<float, 576> samples;
Array<float, MP3::granule_size> samples;
Array<Array<float, 18>, 32> filter_bank_input;
Array<Array<float, 32>, 18> pcm;
u32 part_2_3_length;
Expand Down

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