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adpcm: encoder and decoder structs are now exported

This commit is contained in:
Trek H 2019-05-22 15:10:02 +09:30
parent 537d5bab73
commit a1fe6c6deb
1 changed files with 25 additions and 25 deletions
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50
codec/adpcm/adpcm.go
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@ -27,7 +27,7 @@ LICENSE
Reference algorithms for ADPCM compression and decompression are in part 6. Reference algorithms for ADPCM compression and decompression are in part 6.
*/ */
// Package adpcm provides encoder and decoder structs to encode and decode PCM to and from ADPCM. // Package adpcm provides Encoder and Decoder structs to encode and decode PCM to and from ADPCM.
package adpcm package adpcm
import ( import (
@ -69,8 +69,8 @@ var stepTable = []int16{
32767, 32767,
} }
// encoder is used to encode to ADPCM from PCM data. // Encoder is used to encode to ADPCM from PCM data.
type encoder struct { type Encoder struct {
// dst is the destination for encoded data. // dst is the destination for encoded data.
dst io.Writer dst io.Writer
@ -79,8 +79,8 @@ type encoder struct {
index int16 index int16
} }
// decoder is used to decode from ADPCM to PCM data. // Decoder is used to decode from ADPCM to PCM data.
type decoder struct { type Decoder struct {
// dst is the output buffer that implements io.Writer and io.Bytewriter, ie. where the decoded PCM data is written to. // dst is the output buffer that implements io.Writer and io.Bytewriter, ie. where the decoded PCM data is written to.
dst io.Writer dst io.Writer
@ -90,9 +90,9 @@ type decoder struct {
step int16 step int16
} }
// NewEncoder retuns a new ADPCM encoder. // NewEncoder retuns a new ADPCM Encoder.
func NewEncoder(dst io.Writer) *encoder { func NewEncoder(dst io.Writer) *Encoder {
e := encoder{ e := Encoder{
dst: dst, dst: dst,
} }
return &e return &e
@ -100,7 +100,7 @@ func NewEncoder(dst io.Writer) *encoder {
// encodeSample takes a single 16 bit PCM sample and // encodeSample takes a single 16 bit PCM sample and
// returns a byte of which the last 4 bits are an encoded ADPCM nibble. // returns a byte of which the last 4 bits are an encoded ADPCM nibble.
func (e *encoder) encodeSample(sample int16) byte { func (e *Encoder) encodeSample(sample int16) byte {
// Find difference between the sample and the previous estimation. // Find difference between the sample and the previous estimation.
delta := capAdd16(sample, -e.est) delta := capAdd16(sample, -e.est)
@ -144,10 +144,10 @@ func (e *encoder) encodeSample(sample int16) byte {
return nib return nib
} }
// calcHead sets the state for the encoder by running the first sample through // calcHead sets the state for the Encoder by running the first sample through
// the encoder, and writing the first sample to the encoder's io.Writer (dst). // the Encoder, and writing the first sample to the Encoder's io.Writer (dst).
// It returns the number of bytes written to the encoder's io.Writer (dst) along with any errors. // It returns the number of bytes written to the Encoder's io.Writer (dst) along with any errors.
func (e *encoder) calcHead(sample []byte, pad bool) (int, error) { func (e *Encoder) calcHead(sample []byte, pad bool) (int, error) {
// Check that we are given 1 sample. // Check that we are given 1 sample.
if len(sample) != byteDepth { if len(sample) != byteDepth {
return 0, fmt.Errorf("length of given byte array is: %v, expected: %v", len(sample), byteDepth) return 0, fmt.Errorf("length of given byte array is: %v, expected: %v", len(sample), byteDepth)
@ -176,10 +176,10 @@ func (e *encoder) calcHead(sample []byte, pad bool) (int, error) {
return n, nil return n, nil
} }
// init initializes the encoder's estimation to the first uncompressed sample and the index to // init initializes the Encoder's estimation to the first uncompressed sample and the index to
// point to a suitable quantizer step size. // point to a suitable quantizer step size.
// The suitable step size is the closest step size in the stepTable to half the absolute difference of the first two samples. // The suitable step size is the closest step size in the stepTable to half the absolute difference of the first two samples.
func (e *encoder) init(samples []byte) { func (e *Encoder) init(samples []byte) {
int1 := int16(binary.LittleEndian.Uint16(samples[:byteDepth])) int1 := int16(binary.LittleEndian.Uint16(samples[:byteDepth]))
int2 := int16(binary.LittleEndian.Uint16(samples[byteDepth:initBytes])) int2 := int16(binary.LittleEndian.Uint16(samples[byteDepth:initBytes]))
e.est = int1 e.est = int1
@ -197,10 +197,10 @@ func (e *encoder) init(samples []byte) {
} }
// Write takes a slice of bytes of arbitrary length representing pcm and encodes it into adpcm. // Write takes a slice of bytes of arbitrary length representing pcm and encodes it into adpcm.
// It writes its output to the encoder's dst. // It writes its output to the Encoder's dst.
// The number of bytes written out is returned along with any error that occured. // The number of bytes written out is returned along with any error that occured.
func (e *encoder) Write(b []byte) (int, error) { func (e *Encoder) Write(b []byte) (int, error) {
// Check that pcm has enough data to initialize decoder. // Check that pcm has enough data to initialize Decoder.
pcmLen := len(b) pcmLen := len(b)
if pcmLen < initBytes { if pcmLen < initBytes {
return 0, fmt.Errorf("length of given byte array must be >= %v", initBytes) return 0, fmt.Errorf("length of given byte array must be >= %v", initBytes)
@ -240,9 +240,9 @@ func (e *encoder) Write(b []byte) (int, error) {
return n, nil return n, nil
} }
// NewDecoder retuns a new ADPCM decoder. // NewDecoder retuns a new ADPCM Decoder.
func NewDecoder(dst io.Writer) *decoder { func NewDecoder(dst io.Writer) *Decoder {
d := decoder{ d := Decoder{
dst: dst, dst: dst,
} }
return &d return &d
@ -250,7 +250,7 @@ func NewDecoder(dst io.Writer) *decoder {
// decodeSample takes a byte, the last 4 bits of which contain a single // decodeSample takes a byte, the last 4 bits of which contain a single
// 4 bit ADPCM nibble, and returns a 16 bit decoded PCM sample. // 4 bit ADPCM nibble, and returns a 16 bit decoded PCM sample.
func (d *decoder) decodeSample(nibble byte) int16 { func (d *Decoder) decodeSample(nibble byte) int16 {
// Calculate difference. // Calculate difference.
var diff int16 var diff int16
if nibble&4 != 0 { if nibble&4 != 0 {
@ -289,10 +289,10 @@ func (d *decoder) decodeSample(nibble byte) int16 {
} }
// Write takes a slice of bytes of arbitrary length representing adpcm and decodes it into pcm. // Write takes a slice of bytes of arbitrary length representing adpcm and decodes it into pcm.
// It writes its output to the decoder's dst. // It writes its output to the Decoder's dst.
// The number of bytes written out is returned along with any error that occured. // The number of bytes written out is returned along with any error that occured.
func (d *decoder) Write(b []byte) (int, error) { func (d *Decoder) Write(b []byte) (int, error) {
// Initialize decoder with first 4 bytes of b. // Initialize Decoder with first 4 bytes of b.
d.est = int16(binary.LittleEndian.Uint16(b[:byteDepth])) d.est = int16(binary.LittleEndian.Uint16(b[:byteDepth]))
d.index = int16(b[byteDepth]) d.index = int16(b[byteDepth])
d.step = stepTable[d.index] d.step = stepTable[d.index]