vendor.github.com.pion.rtp.pkg.obu.leb128.go Maven / Gradle / Ivy
// Package obu implements tools for working with the "Open Bitstream Unit"
package obu
import "errors"
const (
sevenLsbBitmask = uint(0b01111111)
msbBitmask = uint(0b10000000)
)
// ErrFailedToReadLEB128 indicates that a buffer ended before a LEB128 value could be successfully read
var ErrFailedToReadLEB128 = errors.New("payload ended before LEB128 was finished")
// EncodeLEB128 encodes a uint as LEB128
func EncodeLEB128(in uint) (out uint) {
for {
// Copy seven bits from in and discard
// what we have copied from in
out |= (in & sevenLsbBitmask)
in >>= 7
// If we have more bits to encode set MSB
// otherwise we are done
if in != 0 {
out |= msbBitmask
out <<= 8
} else {
return out
}
}
}
func decodeLEB128(in uint) (out uint) {
for {
// Take 7 LSB from in
out |= (in & sevenLsbBitmask)
// Discard the MSB
in >>= 8
if in == 0 {
return out
}
out <<= 7
}
}
// ReadLeb128 scans an buffer and decodes a Leb128 value.
// If the end of the buffer is reached and all MSB are set
// an error is returned
func ReadLeb128(in []byte) (uint, uint, error) {
var encodedLength uint
for i := range in {
encodedLength |= uint(in[i])
if in[i]&byte(msbBitmask) == 0 {
return decodeLEB128(encodedLength), uint(i + 1), nil
}
// Make more room for next read
encodedLength <<= 8
}
return 0, 0, ErrFailedToReadLEB128
}