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decode.go
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decode.go
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package vorbis
import "errors"
type floorData struct {
floor floor
data interface{}
noResidue bool
}
func (d *Decoder) decodePacket(r *bitReader, out []float32) ([]float32, error) {
if r.ReadBool() {
return nil, errors.New("vorbis: decoding error")
}
modeNumber := r.Read8(ilog(len(d.modes) - 1))
mode := d.modes[modeNumber]
// decode window type
blocktype := mode.blockflag
longWindow := mode.blockflag == 1
blocksize := d.blocksize[blocktype]
spectrumSize := uint32(blocksize / 2)
windowPrev, windowNext := false, false
window := windowType{blocksize, blocksize, blocksize}
if longWindow {
windowPrev = r.ReadBool()
windowNext = r.ReadBool()
if !windowPrev {
window.prev = d.blocksize[0]
}
if !windowNext {
window.next = d.blocksize[0]
}
}
mapping := &d.mappings[mode.mapping]
floors := make([]floorData, d.channels)
residueVectors := make([][]float32, d.channels)
for ch := range residueVectors {
residueVectors[ch] = d.residueBuffer[ch][:spectrumSize]
for i := range residueVectors[ch] {
residueVectors[ch][i] = 0
}
}
d.decodeFloors(r, floors, mapping, spectrumSize)
d.decodeResidue(r, residueVectors, mapping, floors, spectrumSize)
d.inverseCoupling(mapping, residueVectors)
d.applyFloor(floors, residueVectors)
// inverse MDCT
raw := make([][]float32, d.channels)
for ch := range raw {
raw[ch] = d.rawBuffer[ch][:blocksize]
imdct(&d.lookup[blocktype], residueVectors[ch], raw[ch])
}
// apply window and overlap
d.applyWindow(&window, raw)
center := blocksize / 2
offset := d.blocksize[1]/4 - d.blocksize[0]/4
n := 0
if d.hasOverlap {
n = blocksize / 2
if longWindow && !windowPrev {
n -= offset
}
if !longWindow && !d.overlapShort {
n += offset
}
if out == nil {
out = make([]float32, n*d.channels)
}
}
if longWindow {
start := 0
if !windowPrev {
start = offset
}
if d.hasOverlap {
for ch := range raw {
for i := 0; i < center-start; i++ {
out[i*d.channels+ch] = raw[ch][start+i] + d.overlap[(start+i)*d.channels+ch]
}
}
}
d.overlapShort = false
} else /*short window*/ {
if d.hasOverlap {
if d.overlapShort {
for ch := range raw {
for i := 0; i < center; i++ {
out[i*d.channels+ch] = raw[ch][i] + d.overlap[(offset+i)*d.channels+ch]
}
}
} else {
for i := 0; i < offset*d.channels; i++ {
out[i] = d.overlap[i]
}
for ch := range raw {
for i := offset; i < offset+center; i++ {
out[i*d.channels+ch] = raw[ch][i-offset] + d.overlap[i*d.channels+ch]
}
}
}
}
d.overlapShort = true
}
if !d.hasOverlap {
n = 0
}
overlapCenter := d.blocksize[1] / 4
oStart := overlapCenter - center/2
oEnd := overlapCenter + center/2
for i := 0; i < oStart*d.channels; i++ {
d.overlap[i] = 0
}
for ch := range raw {
for i := oStart; i < oEnd; i++ {
d.overlap[i*d.channels+ch] = raw[ch][center+i-oStart]
}
}
for i := oEnd * d.channels; i < len(d.overlap); i++ {
d.overlap[i] = 0
}
d.hasOverlap = true
return out[:n*d.channels], nil
}
func (d *Decoder) decodeFloors(r *bitReader, floors []floorData, mapping *mapping, n uint32) {
for ch := range floors {
floor := d.floors[mapping.submaps[mapping.mux[ch]].floor]
data := floor.Decode(r, d.codebooks, n)
floors[ch] = floorData{floor, data, data == nil}
}
for i := 0; i < int(mapping.couplingSteps); i++ {
if !floors[mapping.magnitude[i]].noResidue || !floors[mapping.angle[i]].noResidue {
floors[mapping.magnitude[i]].noResidue = false
floors[mapping.angle[i]].noResidue = false
}
}
}
func (d *Decoder) decodeResidue(r *bitReader, out [][]float32, mapping *mapping, floors []floorData, n uint32) {
for i := range mapping.submaps {
doNotDecode := make([]bool, 0, len(out))
tmp := make([][]float32, 0, len(out))
for j := 0; j < d.channels; j++ {
if mapping.mux[j] == uint8(i) {
doNotDecode = append(doNotDecode, floors[j].noResidue)
tmp = append(tmp, out[j])
}
}
d.residues[mapping.submaps[i].residue].Decode(r, doNotDecode, n, d.codebooks, tmp)
}
}
func (d *Decoder) inverseCoupling(mapping *mapping, residueVectors [][]float32) {
for i := mapping.couplingSteps; i > 0; i-- {
magnitudeVector := residueVectors[mapping.magnitude[i-1]]
angleVector := residueVectors[mapping.angle[i-1]]
for j := range magnitudeVector {
m := magnitudeVector[j]
a := angleVector[j]
if m > 0 {
if a > 0 {
m, a = m, m-a
} else {
a, m = m, m+a
}
} else {
if a > 0 {
m, a = m, m+a
} else {
a, m = m, m-a
}
}
magnitudeVector[j] = m
angleVector[j] = a
}
}
}
func (d *Decoder) applyFloor(floors []floorData, residueVectors [][]float32) {
for ch := range residueVectors {
if floors[ch].data != nil {
floors[ch].floor.Apply(residueVectors[ch], floors[ch].data)
} else {
for i := range residueVectors[ch] {
residueVectors[ch][i] = 0
}
}
}
}