mirror of
https://codeberg.org/forgejo/forgejo.git
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230 lines
5.7 KiB
Go
230 lines
5.7 KiB
Go
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package govarint
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import "encoding/binary"
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import "io"
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type U32VarintEncoder interface {
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PutU32(x uint32) int
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Close()
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}
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type U32VarintDecoder interface {
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GetU32() (uint32, error)
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}
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///
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type U64VarintEncoder interface {
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PutU64(x uint64) int
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Close()
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}
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type U64VarintDecoder interface {
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GetU64() (uint64, error)
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}
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///
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type U32GroupVarintEncoder struct {
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w io.Writer
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index int
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store [4]uint32
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temp [17]byte
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}
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func NewU32GroupVarintEncoder(w io.Writer) *U32GroupVarintEncoder { return &U32GroupVarintEncoder{w: w} }
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func (b *U32GroupVarintEncoder) Flush() (int, error) {
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// TODO: Is it more efficient to have a tailored version that's called only in Close()?
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// If index is zero, there are no integers to flush
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if b.index == 0 {
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return 0, nil
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}
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// In the case we're flushing (the group isn't of size four), the non-values should be zero
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// This ensures the unused entries are all zero in the sizeByte
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for i := b.index; i < 4; i++ {
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b.store[i] = 0
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}
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length := 1
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// We need to reset the size byte to zero as we only bitwise OR into it, we don't overwrite it
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b.temp[0] = 0
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for i, x := range b.store {
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size := byte(0)
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shifts := []byte{24, 16, 8, 0}
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for _, shift := range shifts {
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// Always writes at least one byte -- the first one (shift = 0)
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// Will write more bytes until the rest of the integer is all zeroes
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if (x>>shift) != 0 || shift == 0 {
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size += 1
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b.temp[length] = byte(x >> shift)
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length += 1
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}
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}
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// We store the size in two of the eight bits in the first byte (sizeByte)
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// 0 means there is one byte in total, hence why we subtract one from size
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b.temp[0] |= (size - 1) << (uint8(3-i) * 2)
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}
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// If we're flushing without a full group of four, remove the unused bytes we computed
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// This enables us to realize it's a partial group on decoding thanks to EOF
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if b.index != 4 {
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length -= 4 - b.index
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}
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_, err := b.w.Write(b.temp[:length])
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return length, err
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}
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func (b *U32GroupVarintEncoder) PutU32(x uint32) (int, error) {
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bytesWritten := 0
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b.store[b.index] = x
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b.index += 1
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if b.index == 4 {
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n, err := b.Flush()
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if err != nil {
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return n, err
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}
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bytesWritten += n
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b.index = 0
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}
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return bytesWritten, nil
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}
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func (b *U32GroupVarintEncoder) Close() {
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// On Close, we flush any remaining values that might not have been in a full group
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b.Flush()
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}
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///
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type U32GroupVarintDecoder struct {
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r io.ByteReader
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group [4]uint32
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pos int
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finished bool
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capacity int
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}
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func NewU32GroupVarintDecoder(r io.ByteReader) *U32GroupVarintDecoder {
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return &U32GroupVarintDecoder{r: r, pos: 4, capacity: 4}
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}
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func (b *U32GroupVarintDecoder) getGroup() error {
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// We should always receive a sizeByte if there are more values to read
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sizeByte, err := b.r.ReadByte()
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if err != nil {
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return err
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}
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// Calculate the size of the four incoming 32 bit integers
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// 0b00 means 1 byte to read, 0b01 = 2, etc
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b.group[0] = uint32((sizeByte >> 6) & 3)
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b.group[1] = uint32((sizeByte >> 4) & 3)
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b.group[2] = uint32((sizeByte >> 2) & 3)
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b.group[3] = uint32(sizeByte & 3)
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//
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for index, size := range b.group {
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b.group[index] = 0
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// Any error that occurs in earlier byte reads should be repeated at the end one
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// Hence we only catch and report the final ReadByte's error
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var err error
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switch size {
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case 0:
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var x byte
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x, err = b.r.ReadByte()
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b.group[index] = uint32(x)
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case 1:
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var x, y byte
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x, _ = b.r.ReadByte()
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y, err = b.r.ReadByte()
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b.group[index] = uint32(x)<<8 | uint32(y)
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case 2:
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var x, y, z byte
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x, _ = b.r.ReadByte()
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y, _ = b.r.ReadByte()
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z, err = b.r.ReadByte()
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b.group[index] = uint32(x)<<16 | uint32(y)<<8 | uint32(z)
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case 3:
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var x, y, z, zz byte
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x, _ = b.r.ReadByte()
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y, _ = b.r.ReadByte()
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z, _ = b.r.ReadByte()
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zz, err = b.r.ReadByte()
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b.group[index] = uint32(x)<<24 | uint32(y)<<16 | uint32(z)<<8 | uint32(zz)
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}
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if err != nil {
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if err == io.EOF {
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// If we hit EOF here, we have found a partial group
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// We've return any valid entries we have read and return EOF once we run out
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b.capacity = index
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b.finished = true
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break
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} else {
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return err
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}
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}
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}
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// Reset the pos pointer to the beginning of the read values
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b.pos = 0
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return nil
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}
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func (b *U32GroupVarintDecoder) GetU32() (uint32, error) {
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// Check if we have any more values to give out - if not, let's get them
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if b.pos == b.capacity {
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// If finished is set, there is nothing else to do
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if b.finished {
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return 0, io.EOF
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}
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err := b.getGroup()
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if err != nil {
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return 0, err
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}
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}
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// Increment pointer and return the value stored at that point
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b.pos += 1
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return b.group[b.pos-1], nil
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}
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///
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type Base128Encoder struct {
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w io.Writer
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tmpBytes []byte
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}
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func NewU32Base128Encoder(w io.Writer) *Base128Encoder {
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return &Base128Encoder{w: w, tmpBytes: make([]byte, binary.MaxVarintLen32)}
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}
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func NewU64Base128Encoder(w io.Writer) *Base128Encoder {
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return &Base128Encoder{w: w, tmpBytes: make([]byte, binary.MaxVarintLen64)}
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}
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func (b *Base128Encoder) PutU32(x uint32) (int, error) {
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writtenBytes := binary.PutUvarint(b.tmpBytes, uint64(x))
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return b.w.Write(b.tmpBytes[:writtenBytes])
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}
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func (b *Base128Encoder) PutU64(x uint64) (int, error) {
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writtenBytes := binary.PutUvarint(b.tmpBytes, x)
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return b.w.Write(b.tmpBytes[:writtenBytes])
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}
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func (b *Base128Encoder) Close() {
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}
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///
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type Base128Decoder struct {
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r io.ByteReader
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}
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func NewU32Base128Decoder(r io.ByteReader) *Base128Decoder { return &Base128Decoder{r: r} }
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func NewU64Base128Decoder(r io.ByteReader) *Base128Decoder { return &Base128Decoder{r: r} }
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func (b *Base128Decoder) GetU32() (uint32, error) {
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v, err := binary.ReadUvarint(b.r)
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return uint32(v), err
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}
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func (b *Base128Decoder) GetU64() (uint64, error) {
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return binary.ReadUvarint(b.r)
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}
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