func riceDecode(br *bit.Reader, n int, M uint) ([]int32, error) {
ns := make([]int32, n)
for i := 0; i < n; i++ {
var q uint64
for {
switch b, err := br.Read(1); {
case err != nil:
return nil, err
case b == 0:
q++
continue
}
break
}
u, err := br.Read(M)
if err != nil {
return nil, err
}
u |= (q << M)
ns[i] = int32(u>>1) ^ -int32(u&1)
}
return ns, nil
}
func decodeLPCSubFrame(br *bit.Reader, sampleSize uint, blkSize int, predO int) ([]int32, error) {
warm, err := readInts(br, predO, sampleSize)
if err != nil {
return nil, err
}
prec, err := br.Read(4)
if err != nil {
return nil, err
} else if prec == 0xF {
return nil, errors.New("Bad LPC predictor precision")
}
prec++
s, err := br.Read(5)
if err != nil {
return nil, err
}
shift := int(signExtend(s, 5))
if shift < 0 {
return nil, errors.New("Invalid negative shift")
}
coeffs, err := readInts(br, predO, uint(prec))
if err != nil {
return nil, err
}
residual, err := decodeResiduals(br, blkSize, predO)
if err != nil {
return nil, err
}
return lpcDecode(coeffs, warm, residual, uint(shift)), nil
}
func utf8Decode(br *bit.Reader) (uint64, error) {
left := 0
v := uint64(0)
switch b0, err := br.Read(8); {
case err != nil:
return 0, err
// 0xxx xxxx
case b0&0x80 == 0:
return uint64(b0 & 0x7F), nil
// 110x xxxx 10xx xxxx
case b0&0xE0 == 0xC0:
left = 1
v = uint64(b0 & 0x1F)
// 1110 xxxx 10xx xxxx 10xx xxxx
case b0&0xF0 == 0xE0:
left = 2
v = uint64(b0 & 0xF)
// 1111 0xxx 10xx xxxx 10xx xxxx 10xx xxxx
case b0&0xF8 == 0xF0:
left = 3
v = uint64(b0 & 0x7)
// 1111 10xx 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx
case b0&0xFC == 0xF8:
left = 4
v = uint64(b0 & 0x3)
// 1111 110x 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx 10xx xxxx
case b0&0xFE == 0xFC:
left = 5
v = uint64(b0 & 0x1)
}
for n := 0; n < left; n++ {
switch b, err := br.Read(8); {
case err == io.EOF:
return 0, io.ErrUnexpectedEOF
case err != nil:
return 0, err
case b&0xC0 != 0x80:
return 0, errors.New("Bad UTF-8 encoding in frame header")
default:
v = (v << 6) | (b & 0x3F)
}
}
return v, nil
}
func readInts(br *bit.Reader, n int, bits uint) ([]int32, error) {
is := make([]int32, n)
for i := range is {
w, err := br.Read(bits)
if err != nil {
return nil, err
}
is[i] = signExtend(w, bits)
}
return is, nil
}
func readSubFrame(br *bit.Reader, h *frameHeader, ch int) ([]int32, error) {
var data []int32
bps := h.bitsPerSample(ch)
kind, order, err := readSubFrameHeader(br)
if err != nil {
return nil, err
}
switch kind {
case subFrameConstant:
v, err := br.Read(bps)
if err != nil {
return nil, err
}
u := signExtend(v, bps)
data = make([]int32, h.blockSize)
for j := range data {
data[j] = u
}
case subFrameVerbatim:
data = make([]int32, h.blockSize)
for j := range data {
v, err := br.Read(bps)
if err != nil {
return nil, err
}
data[j] = signExtend(v, bps)
}
case subFrameFixed:
data, err = decodeFixedSubFrame(br, bps, h.blockSize, order)
if err != nil {
return nil, err
}
case subFrameLPC:
data, err = decodeLPCSubFrame(br, bps, h.blockSize, order)
if err != nil {
return nil, err
}
default:
return nil, errors.New("Unsupported frame kind")
}
return data, nil
}
func readSubFrameHeader(br *bit.Reader) (kind subFrameKind, order int, err error) {
switch pad, err := br.Read(1); {
case err != nil:
return 0, 0, err
case pad != 0:
// Do nothing, but this is a bad padding value.
}
switch k, err := br.Read(6); {
case err != nil:
return 0, 0, err
case k == 0:
kind = subFrameConstant
case k == 1:
kind = subFrameVerbatim
case (k&0x3E == 0x02) || (k&0x3C == 0x04) || (k&0x30 == 0x10):
return 0, 0, errors.New("Bad subframe type")
case k&0x38 == 0x08:
if order = int(k & 0x07); order > 4 {
return 0, 0, errors.New("Bad subframe type")
}
kind = subFrameFixed
case k&0x20 == 0x20:
order = int(k&0x1F) + 1
kind = subFrameLPC
default:
return 0, 0, errors.New("Invalid subframe type")
}
n := 0
switch k, err := br.Read(1); {
case err != nil:
return 0, 0, err
case k == 1:
n++
k = uint64(0)
for k == 0 {
if k, err = br.Read(1); err != nil {
return 0, 0, err
}
n++
}
}
return kind, order, nil
}
func decodeResiduals(br *bit.Reader, blkSize int, predO int) ([]int32, error) {
var bits uint
switch method, err := br.Read(2); {
case err != nil:
return nil, err
case method == 0:
bits = 4
case method == 1:
bits = 5
default:
return nil, errors.New("Bad residual method")
}
partO, err := br.Read(4)
if err != nil {
return nil, err
}
var residue []int32
for i := 0; i < 1<<partO; i++ {
M, err := br.Read(bits)
if err != nil {
return nil, err
} else if (bits == 4 && M == 0xF) || (bits == 5 && M == 0x1F) {
return nil, errors.New("Unsupported, unencoded residuals")
}
n := 0
switch {
case partO == 0:
n = blkSize - predO
case i > 0:
n = blkSize / (1 << partO)
default:
n = (blkSize / (1 << partO)) - predO
}
r, err := riceDecode(br, n, uint(M))
if err != nil {
return nil, err
}
residue = append(residue, r...)
}
return residue, nil
}