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