mirror of
https://github.com/hajimehoshi/ebiten.git
synced 2024-12-26 03:38:55 +01:00
250 lines
7.3 KiB
Go
250 lines
7.3 KiB
Go
// Copyright 2017 The Ebiten Authors
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// +build !js
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package mp3
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import (
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"fmt"
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"io"
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)
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func readCRC() error {
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buf := make([]int, 2)
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n := 0
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var err error
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for n < 2 && err == nil {
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nn, err2 := getBytes(buf[n:])
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n += nn
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err = err2
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}
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if err == io.EOF {
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if n < 2 {
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return fmt.Errorf("mp3: unexpected EOF at readCRC")
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}
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return nil
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}
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if err != nil {
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return err
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}
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return nil
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}
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func readFrame() (*frame, error) {
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f := &frame{}
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if err := f.readHeader(); err != nil {
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return nil, err
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}
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// Get CRC word if present
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if f.header.protection_bit == 0 {
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if err := readCRC(); err != nil {
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return nil, err
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}
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}
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if f.header.layer != mpeg1Layer3 {
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return nil, fmt.Errorf("mp3: only layer3 (want %d; got %d) is supported!", mpeg1Layer3, f.header.layer)
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}
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// Get side info
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if err := f.readAudioL3(); err != nil {
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return nil, err
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}
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// If there's not enough main data in the bit reservoir,
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// signal to calling function so that decoding isn't done!
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// Get main data(scalefactors and Huffman coded frequency data)
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if err := f.readMainL3(); err != nil {
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return nil, err
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}
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return f, nil
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}
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func isHeader(header uint32) bool {
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const C_SYNC = 0xffe00000
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if (header & C_SYNC) != C_SYNC {
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return false
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}
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// Bitrate must not be 15.
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if (header & (0xf << 12)) == 0xf<<12 {
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return false
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}
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// Sample Frequency must not be 3.
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if (header & (3 << 10)) == 3<<10 {
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return false
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}
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return true
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}
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func (f *frame) readHeader() error {
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/* Get the next four bytes from the bitstream */
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buf := make([]int, 4)
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n := 0
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var err error
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for n < 4 && err == nil {
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nn, err2 := getBytes(buf[n:])
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n += nn
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err = err2
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}
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if n < 4 {
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if err == io.EOF {
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return fmt.Errorf("mp3: unexpected EOF at readHeader")
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}
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return err
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}
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b1 := uint32(buf[0])
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b2 := uint32(buf[1])
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b3 := uint32(buf[2])
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b4 := uint32(buf[3])
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header := (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
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for !isHeader(uint32(header)) {
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/* No,so scan the bitstream one byte at a time until we find it or EOF */
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/* Shift the values one byte to the left */
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b1 = b2
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b2 = b3
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b3 = b4
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/* Get one new byte from the bitstream */
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b, err := getByte()
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if err != nil {
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if err == io.EOF {
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return fmt.Errorf("mp3: unexpected EOF at readHeader")
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}
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return err
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}
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b4 = uint32(b)
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header = (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
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} /* while... */
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/* If we get here we've found the sync word,and can decode the header
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* which is in the low 20 bits of the 32-bit sync+header word. */
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/* Decode the header */
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f.header.id = int((header & 0x00180000) >> 19)
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f.header.layer = mpeg1Layer((header & 0x00060000) >> 17)
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f.header.protection_bit = int((header & 0x00010000) >> 16)
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f.header.bitrate_index = int((header & 0x0000f000) >> 12)
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f.header.sampling_frequency = int((header & 0x00000c00) >> 10)
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f.header.padding_bit = int((header & 0x00000200) >> 9)
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f.header.private_bit = int((header & 0x00000100) >> 8)
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f.header.mode = mpeg1Mode((header & 0x000000c0) >> 6)
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f.header.mode_extension = int((header & 0x00000030) >> 4)
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f.header.copyright = int((header & 0x00000008) >> 3)
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f.header.original_or_copy = int((header & 0x00000004) >> 2)
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f.header.emphasis = int((header & 0x00000003) >> 0)
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/* Check for invalid values and impossible combinations */
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if f.header.id != 3 {
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return fmt.Errorf("mp3: ID must be 3. Header word is 0x%08x at file pos %d",
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header, getFilepos())
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}
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if f.header.bitrate_index == 0 {
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return fmt.Errorf("mp3: Free bitrate format NIY! Header word is 0x%08x at file pos %d",
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header, getFilepos())
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}
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if f.header.bitrate_index == 15 {
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return fmt.Errorf("mp3: bitrate_index = 15 is invalid! Header word is 0x%08x at file pos %d",
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header, getFilepos())
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}
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if f.header.sampling_frequency == 3 {
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return fmt.Errorf("mp3: sampling_frequency = 3 is invalid! Header word is 0x%08x at file pos %d",
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header, getFilepos())
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}
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if f.header.layer == mpeg1LayerReserved {
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return fmt.Errorf("mp3: layer = %d is invalid! Header word is 0x%08x at file pos %d",
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mpeg1LayerReserved, header, getFilepos())
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}
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return nil
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}
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func (f *frame) readHuffman(part_2_start, gr, ch int) error {
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/* Check that there is any data to decode. If not,zero the array. */
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if f.sideInfo.part2_3_length[gr][ch] == 0 {
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for is_pos := 0; is_pos < 576; is_pos++ {
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f.mainData.is[gr][ch][is_pos] = 0.0
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}
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return nil
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}
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/* Calculate bit_pos_end which is the index of the last bit for this part. */
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bit_pos_end := part_2_start + f.sideInfo.part2_3_length[gr][ch] - 1
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/* Determine region boundaries */
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region_1_start := 0
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region_2_start := 0
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if (f.sideInfo.win_switch_flag[gr][ch] == 1) && (f.sideInfo.block_type[gr][ch] == 2) {
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region_1_start = 36 /* sfb[9/3]*3=36 */
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region_2_start = 576 /* No Region2 for short block case. */
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} else {
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sfreq := f.header.sampling_frequency
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region_1_start =
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sfBandIndicesSet[sfreq].l[f.sideInfo.region0_count[gr][ch]+1]
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region_2_start =
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sfBandIndicesSet[sfreq].l[f.sideInfo.region0_count[gr][ch]+
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f.sideInfo.region1_count[gr][ch]+2]
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}
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/* Read big_values using tables according to region_x_start */
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for is_pos := 0; is_pos < f.sideInfo.big_values[gr][ch]*2; is_pos++ {
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table_num := 0
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if is_pos < region_1_start {
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table_num = f.sideInfo.table_select[gr][ch][0]
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} else if is_pos < region_2_start {
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table_num = f.sideInfo.table_select[gr][ch][1]
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} else {
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table_num = f.sideInfo.table_select[gr][ch][2]
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}
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/* Get next Huffman coded words */
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x, y, _, _, err := huffmanDecode(table_num)
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if err != nil {
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return err
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}
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/* In the big_values area there are two freq lines per Huffman word */
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f.mainData.is[gr][ch][is_pos] = float32(x)
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is_pos++
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f.mainData.is[gr][ch][is_pos] = float32(y)
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}
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/* Read small values until is_pos = 576 or we run out of huffman data */
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table_num := f.sideInfo.count1table_select[gr][ch] + 32
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is_pos := f.sideInfo.big_values[gr][ch] * 2
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for ; (is_pos <= 572) && (getMainPos() <= bit_pos_end); is_pos++ {
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/* Get next Huffman coded words */
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x, y, v, w, err := huffmanDecode(table_num)
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if err != nil {
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return err
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}
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f.mainData.is[gr][ch][is_pos] = float32(v)
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is_pos++
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if is_pos >= 576 {
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break
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}
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f.mainData.is[gr][ch][is_pos] = float32(w)
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is_pos++
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if is_pos >= 576 {
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break
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}
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f.mainData.is[gr][ch][is_pos] = float32(x)
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is_pos++
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if is_pos >= 576 {
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break
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}
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f.mainData.is[gr][ch][is_pos] = float32(y)
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}
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/* Check that we didn't read past the end of this section */
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if getMainPos() > (bit_pos_end + 1) {
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/* Remove last words read */
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is_pos -= 4
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}
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/* Setup count1 which is the index of the first sample in the rzero reg. */
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f.sideInfo.count1[gr][ch] = is_pos
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/* Zero out the last part if necessary */
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for ; /* is_pos comes from last for-loop */ is_pos < 576; is_pos++ {
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f.mainData.is[gr][ch][is_pos] = 0.0
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}
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/* Set the bitpos to point to the next part to read */
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setMainPos(bit_pos_end + 1)
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return nil
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}
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