// decodeRiceResidual decodes a Rice encoded residual (error signal).
func (subframe *Subframe) decodeRiceResidual(br *bits.Reader, k uint) error {
// Read unary encoded most significant bits.
high, err := br.ReadUnary()
if err != nil {
return unexpected(err)
}
// Read binary encoded least significant bits.
low, err := br.Read(k)
if err != nil {
return unexpected(err)
}
residual := int32(high<<k | low)
// ZigZag decode.
residual = bits.ZigZag(residual)
subframe.Samples = append(subframe.Samples, residual)
return nil
}
// parseHeader reads and parses the header of a subframe.
func (subframe *Subframe) parseHeader(br *bits.Reader) error {
// 1 bit: zero-padding.
x, err := br.Read(1)
if err != nil {
return unexpected(err)
}
if x != 0 {
return errors.New("frame.Subframe.parseHeader: non-zero padding")
}
// 6 bits: Pred.
x, err = br.Read(6)
if err != nil {
return unexpected(err)
}
// The 6 bits are used to specify the prediction method and order as follows:
// 000000: Constant prediction method.
// 000001: Verbatim prediction method.
// 00001x: reserved.
// 0001xx: reserved.
// 001xxx:
// if (xxx <= 4)
// Fixed prediction method; xxx=order
// else
// reserved.
// 01xxxx: reserved.
// 1xxxxx: FIR prediction method; xxxxx=order-1
switch {
case x < 1:
// 000000: Constant prediction method.
subframe.Pred = PredConstant
case x < 2:
// 000001: Verbatim prediction method.
subframe.Pred = PredVerbatim
case x < 8:
// 00001x: reserved.
// 0001xx: reserved.
return fmt.Errorf("frame.Subframe.parseHeader: reserved prediction method bit pattern (%06b)", x)
case x < 16:
// 001xxx:
// if (xxx <= 4)
// Fixed prediction method; xxx=order
// else
// reserved.
order := int(x & 0x07)
if order > 4 {
return fmt.Errorf("frame.Subframe.parseHeader: reserved prediction method bit pattern (%06b)", x)
}
subframe.Pred = PredFixed
subframe.Order = order
case x < 32:
// 01xxxx: reserved.
return fmt.Errorf("frame.Subframe.parseHeader: reserved prediction method bit pattern (%06b)", x)
default:
// 1xxxxx: FIR prediction method; xxxxx=order-1
subframe.Pred = PredFIR
subframe.Order = int(x&0x1F) + 1
}
// 1 bit: hasWastedBits.
x, err = br.Read(1)
if err != nil {
return unexpected(err)
}
if x != 0 {
// k wasted bits-per-sample in source subblock, k-1 follows, unary coded;
// e.g. k=3 => 001 follows, k=7 => 0000001 follows.
x, err = br.ReadUnary()
if err != nil {
return unexpected(err)
}
subframe.Wasted = uint(x) + 1
}
return nil
}