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audio/mp3: Refactoring

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This commit is contained in:
Hajime Hoshi 2017-06-18 16:50:08 +09:00
parent 0291330a1b
commit e0661a0ac6
1 changed files with 28 additions and 26 deletions
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54
audio/mp3/read.go
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@ -88,7 +88,7 @@ func isHeader(header uint32) bool {
}
func (f *frame) readHeader() error {
/* Get the next four bytes from the bitstream */
// Get the next four bytes from the bitstream
buf := make([]int, 4)
n := 0
var err error
@ -112,12 +112,12 @@ func (f *frame) readHeader() error {
b4 := uint32(buf[3])
header := (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
for !isHeader(uint32(header)) {
/* No,so scan the bitstream one byte at a time until we find it or EOF */
/* Shift the values one byte to the left */
// No,so scan the bitstream one byte at a time until we find it or EOF
// Shift the values one byte to the left
b1 = b2
b2 = b3
b3 = b4
/* Get one new byte from the bitstream */
// Get one new byte from the bitstream
b, err := getByte()
if err != nil {
if err == io.EOF {
@ -127,10 +127,10 @@ func (f *frame) readHeader() error {
}
b4 = uint32(b)
header = (b1 << 24) | (b2 << 16) | (b3 << 8) | (b4 << 0)
} /* while... */
/* If we get here we've found the sync word,and can decode the header
* which is in the low 20 bits of the 32-bit sync+header word. */
/* Decode the header */
}
// If we get here we've found the sync word,and can decode the header
// which is in the low 20 bits of the 32-bit sync+header word.
// Decode the header
f.header.id = int((header & 0x00180000) >> 19)
f.header.layer = mpeg1Layer((header & 0x00060000) >> 17)
f.header.protection_bit = int((header & 0x00010000) >> 16)
@ -143,7 +143,7 @@ func (f *frame) readHeader() error {
f.header.copyright = int((header & 0x00000008) >> 3)
f.header.original_or_copy = int((header & 0x00000004) >> 2)
f.header.emphasis = int((header & 0x00000003) >> 0)
/* Check for invalid values and impossible combinations */
// Check for invalid values and impossible combinations
if f.header.id != 3 {
return fmt.Errorf("mp3: ID must be 3. Header word is 0x%08x at file pos %d",
header, getFilepos())
@ -168,21 +168,21 @@ func (f *frame) readHeader() error {
}
func (f *frame) readHuffman(part_2_start, gr, ch int) error {
/* Check that there is any data to decode. If not,zero the array. */
// Check that there is any data to decode. If not,zero the array.
if f.sideInfo.part2_3_length[gr][ch] == 0 {
for is_pos := 0; is_pos < 576; is_pos++ {
f.mainData.is[gr][ch][is_pos] = 0.0
}
return nil
}
/* Calculate bit_pos_end which is the index of the last bit for this part. */
// Calculate bit_pos_end which is the index of the last bit for this part.
bit_pos_end := part_2_start + f.sideInfo.part2_3_length[gr][ch] - 1
/* Determine region boundaries */
// Determine region boundaries
region_1_start := 0
region_2_start := 0
if (f.sideInfo.win_switch_flag[gr][ch] == 1) && (f.sideInfo.block_type[gr][ch] == 2) {
region_1_start = 36 /* sfb[9/3]*3=36 */
region_2_start = 576 /* No Region2 for short block case. */
region_1_start = 36 // sfb[9/3]*3=36
region_2_start = 576 // No Region2 for short block case.
} else {
sfreq := f.header.sampling_frequency
region_1_start =
@ -191,7 +191,7 @@ func (f *frame) readHuffman(part_2_start, gr, ch int) error {
sfBandIndicesSet[sfreq].l[f.sideInfo.region0_count[gr][ch]+
f.sideInfo.region1_count[gr][ch]+2]
}
/* Read big_values using tables according to region_x_start */
// Read big_values using tables according to region_x_start
for is_pos := 0; is_pos < f.sideInfo.big_values[gr][ch]*2; is_pos++ {
table_num := 0
if is_pos < region_1_start {
@ -201,21 +201,21 @@ func (f *frame) readHuffman(part_2_start, gr, ch int) error {
} else {
table_num = f.sideInfo.table_select[gr][ch][2]
}
/* Get next Huffman coded words */
// Get next Huffman coded words
x, y, _, _, err := huffmanDecode(f.mainDataBytes, table_num)
if err != nil {
return err
}
/* In the big_values area there are two freq lines per Huffman word */
// In the big_values area there are two freq lines per Huffman word
f.mainData.is[gr][ch][is_pos] = float32(x)
is_pos++
f.mainData.is[gr][ch][is_pos] = float32(y)
}
/* Read small values until is_pos = 576 or we run out of huffman data */
// Read small values until is_pos = 576 or we run out of huffman data
table_num := f.sideInfo.count1table_select[gr][ch] + 32
is_pos := f.sideInfo.big_values[gr][ch] * 2
for ; (is_pos <= 572) && (f.mainDataBytes.getMainPos() <= bit_pos_end); is_pos++ {
/* Get next Huffman coded words */
for (is_pos <= 572) && (f.mainDataBytes.getMainPos() <= bit_pos_end) {
// Get next Huffman coded words
x, y, v, w, err := huffmanDecode(f.mainDataBytes, table_num)
if err != nil {
return err
@ -236,19 +236,21 @@ func (f *frame) readHuffman(part_2_start, gr, ch int) error {
break
}
f.mainData.is[gr][ch][is_pos] = float32(y)
is_pos++
}
/* Check that we didn't read past the end of this section */
// Check that we didn't read past the end of this section
if f.mainDataBytes.getMainPos() > (bit_pos_end + 1) {
/* Remove last words read */
// Remove last words read
is_pos -= 4
}
/* Setup count1 which is the index of the first sample in the rzero reg. */
// Setup count1 which is the index of the first sample in the rzero reg.
f.sideInfo.count1[gr][ch] = is_pos
/* Zero out the last part if necessary */
for ; /* is_pos comes from last for-loop */ is_pos < 576; is_pos++ {
// Zero out the last part if necessary
for is_pos < 576 {
f.mainData.is[gr][ch][is_pos] = 0.0
is_pos++
}
/* Set the bitpos to point to the next part to read */
// Set the bitpos to point to the next part to read
f.mainDataBytes.setMainPos(bit_pos_end + 1)
return nil
}