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rle.go
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rle.go
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package rle
import (
"bytes"
"encoding/binary"
"fmt"
"io"
"github.com/inigolabs/parquet/internal/bitpack"
)
const (
mask1 = uint64(0x7F)
mask2 = uint64(0x80)
)
// RLE holds metadata that is used while reading
// and writing run length encoded data.
type RLE struct {
// TODO: make out a buffer?
out *writeBuffer
bitWidth int32
packBuf []byte
prev uint8
valBuf []uint8
bufCount int
repeatCount int
groupCount int
headerPointer int
}
// New creates an RLE struct based on the maximum bitwidth (width) of
// the data that is to be encoded/decoded.
func New(width int32, size int) (*RLE, error) {
if width > 4 {
return nil, fmt.Errorf("bitwidth %d is greater than 4 (highest supported)", width)
}
return &RLE{
out: newWriteBuffer(size),
bitWidth: width,
packBuf: make([]byte, int(width)),
valBuf: make([]uint8, 8),
headerPointer: -1,
}, nil
}
// Write encodes 'value' to run length encoded data.
func (r *RLE) Write(value uint8) {
if value == r.prev {
r.repeatCount++
if r.repeatCount >= 8 {
return
}
} else {
if r.repeatCount >= 8 {
r.writeRLERun()
}
r.repeatCount = 1
r.prev = value
}
r.valBuf[r.bufCount] = value
r.bufCount++
if r.bufCount == 8 {
r.writeOrAppendBitPackedRun()
}
}
func (r *RLE) writeOrAppendBitPackedRun() {
if r.groupCount >= 63 {
r.endPreviousBitPackedRun()
}
if r.headerPointer == -1 {
r.out.write([]byte{0})
r.headerPointer = r.out.size() - 1
}
tmp := make([]byte, 0, bitpack.MaxSize)
tmp = bitpack.Pack(tmp, int(r.bitWidth), r.valBuf)
r.out.write(tmp)
r.bufCount = 0
r.repeatCount = 0
r.groupCount++
}
func (r *RLE) endPreviousBitPackedRun() {
if r.headerPointer == -1 {
return
}
bitPackHeader := byte((r.groupCount << 1) | 1)
r.out.writeAt([]byte{bitPackHeader}, r.headerPointer)
r.headerPointer = -1
r.groupCount = 0
}
func (r *RLE) writeRLERun() error {
r.endPreviousBitPackedRun()
r.out.write(r.leb128(r.repeatCount << 1))
x, err := r.writeIntLittleEndianPaddedOnBitWidth(r.prev, r.bitWidth)
if err != nil {
return err
}
r.out.write(x)
r.repeatCount = 0
r.bufCount = 0
return nil
}
func (r *RLE) writeIntLittleEndianPaddedOnBitWidth(v uint8, bitWidth int32) ([]byte, error) {
bytesWidth := (bitWidth + 7) / 8
switch bytesWidth {
case 0:
return nil, nil
case 1:
return []byte{
byte(uint(v>>0) & 0xFF),
}, nil
case 2:
return []byte{
byte(uint(v>>0) & 0xFF),
byte(uint(v>>8) & 0xFF),
}, nil
default:
return nil, fmt.Errorf("Encountered value (%d) that requires more than 2 bytes", v)
}
}
func (r *RLE) leb128(value int) []byte {
var out []byte
for (value & 0xFFFFFF80) != 0 {
out = append(out, byte((value&0x7F)|0x80))
value = int(uint(value) >> 7)
}
return append(out, byte(value&0x7F))
}
// Bytes the raw run length encoded data.
func (r *RLE) Bytes() []byte {
if r.repeatCount >= 8 {
r.writeRLERun()
} else if r.bufCount > 0 {
for i := r.bufCount; i < 8; i++ {
r.valBuf[i] = 0
}
r.writeOrAppendBitPackedRun()
r.endPreviousBitPackedRun()
} else {
r.endPreviousBitPackedRun()
}
var b bytes.Buffer
binary.Write(&b, binary.LittleEndian, int32(r.out.size()))
return append(b.Bytes(), r.out.bytes()...)
}
// Read reads the RLE encoded definition levels
func (r *RLE) Read(in io.Reader) ([]uint8, int, error) {
var out []uint8
var length int32
if err := binary.Read(in, binary.LittleEndian, &length); err != nil {
return out, 0, err
}
buf := make([]byte, length)
if _, err := in.Read(buf); err != nil {
return nil, 0, err
}
rr := bytes.NewReader(buf)
var header uint64
var vals []uint8
var err error
for rr.Len() > 0 {
header, err = readLEB128(rr)
if err != nil {
return nil, 0, err
}
if header&1 == 0 {
vals, err = readRLE(rr, header, uint64(r.bitWidth))
if err != nil {
return nil, 0, err
}
out = append(out, vals...)
} else {
vals, err = readRLEBitPacked(rr, header, uint8(r.bitWidth))
if err != nil {
return nil, 0, err
}
out = append(out, vals...)
}
}
return out, int(length) + 4, nil
}
func readRLEBitPacked(r io.Reader, header uint64, width uint8) ([]uint8, error) {
count := (int(header) >> 1) * 8
if width == 0 {
return make([]uint8, count), nil
}
byteCount := (int(width) * count) / 8
rawBytes := make([]byte, byteCount)
if _, err := r.Read(rawBytes); err != nil {
return nil, err
}
var out []uint8
for len(rawBytes) > 0 {
out = append(out, bitpack.Unpack(int(width), rawBytes[:width])...)
rawBytes = rawBytes[int(width):]
}
return out, nil
}
func readRLE(r io.Reader, header uint64, bitWidth uint64) ([]uint8, error) {
count := header >> 1
value, err := readIntLittleEndianPaddedOnBitWidth(r, int(bitWidth))
if err != nil {
return nil, err
}
out := make([]uint8, count)
for i := 0; i < int(count); i++ {
out[i] = uint8(value)
}
return out, nil
}
func readIntLittleEndianPaddedOnBitWidth(in io.Reader, bitWidth int) (uint8, error) {
bytesWidth := (bitWidth + 7) / 8
switch bytesWidth {
case 0:
return 0, nil
case 1:
return readIntLittleEndianOnOneByte(in)
case 2:
return readIntLittleEndianOnTwoBytes(in)
default:
return 0, fmt.Errorf("Encountered bitWidth (%d) that requires more than 4 bytes", bitWidth)
}
}
func readIntLittleEndianOnOneByte(in io.Reader) (uint8, error) {
b := make([]byte, 1)
_, err := in.Read(b)
if err != nil {
return 0, err
}
if b[0] < 0 {
return 0, io.EOF
}
return uint8(b[0]), nil
}
func readIntLittleEndianOnTwoBytes(in io.Reader) (uint8, error) {
b := make([]byte, 2)
_, err := in.Read(b)
if err != nil {
return 0, err
}
if b[0] < 0 {
return 0, io.EOF
}
if (b[0] | b[1]) < 0 {
return 0, io.EOF
}
return (uint8(b[1]) << 8) + (uint8(b[0]) << 0), nil
}
func readLEB128(r io.Reader) (uint64, error) {
var err error
var out, shift, x uint64
b := make([]byte, 1)
for {
_, err = r.Read(b)
if err != nil {
return out, err
}
x = uint64(b[0])
out |= (x & mask1) << shift
if (x & mask2) == 0 {
return out, nil
}
shift += 7
}
}