status-go/vendor/github.com/pion/rtp/codecs/av1/obu/leb128.go

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// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT
// Package obu implements tools for working with the Open Bitstream Unit.
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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
}
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// WriteToLeb128 writes a uint to a LEB128 encoded byte slice.
func WriteToLeb128(in uint) []byte {
b := make([]byte, 10)
for i := 0; i < len(b); i++ {
b[i] = byte(in & 0x7f)
in >>= 7
if in == 0 {
return b[:i+1]
}
b[i] |= 0x80
}
return b // unreachable
}