65 lines
1.4 KiB
Go
65 lines
1.4 KiB
Go
package common
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import "log"
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// BitStream is a utility class for reading groups of bits from a stream
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type BitStream struct {
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data []byte
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dataPosition int
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current int
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bitCount int
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}
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// CreateBitStream creates a new BitStream
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func CreateBitStream(newData []byte) *BitStream {
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result := &BitStream{
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data: newData,
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dataPosition: 0,
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current: 0,
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bitCount: 0,
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}
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return result
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}
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// ReadBits reads the specified number of bits and returns the value
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func (v *BitStream) ReadBits(bitCount int) int {
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if bitCount > 16 {
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log.Panic("Maximum BitCount is 16")
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}
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if !v.EnsureBits(bitCount) {
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return -1
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}
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result := v.current & (0xffff >> uint(16-bitCount))
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v.WasteBits(bitCount)
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return result
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}
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// PeekByte returns the current byte without adjusting the position
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func (v *BitStream) PeekByte() int {
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if !v.EnsureBits(8) {
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return -1
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}
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return v.current & 0xff
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}
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// EnsureBits ensures that the specified number of bits are available
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func (v *BitStream) EnsureBits(bitCount int) bool {
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if bitCount <= v.bitCount {
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return true
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}
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if v.dataPosition >= len(v.data) {
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return false
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}
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nextValue := v.data[v.dataPosition]
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v.dataPosition++
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v.current |= int(nextValue) << uint(v.bitCount)
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v.bitCount += 8
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return true
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}
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// WasteBits dry-reads the specified number of bits
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func (v *BitStream) WasteBits(bitCount int) {
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v.current >>= uint(bitCount)
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v.bitCount -= bitCount
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}
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