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tszlong.go
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tszlong.go
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// Package tsz implements time-series compression
// it is a fork of https://github.com/dgryski/go-tsz
// which implements http://www.vldb.org/pvldb/vol8/p1816-teller.pdf
// see devdocs/chunk-format.md for more info
package tsz
import (
"bytes"
"math"
"math/bits"
"sync"
)
// SeriesLong similar to Series4h, except:
// * it doesn't write t0 to the stream (for callers that track t0 corresponding to a chunk separately)
// * it doesn't store an initial delta. instead, it assumes a starting delta of 60 and uses delta-of-delta
// encoding from the get-go.
// * it uses a more compact way to mark end-of-stream
type SeriesLong struct {
sync.Mutex
// TODO(dgryski): timestamps in the paper are uint64
T0 uint32 // exposed for caller convenience. do NOT set directly. set via constructor
T uint32 // exposed for caller convenience. do NOT set directly. may only be set via Push()
val float64
bw bstream
leading uint8
trailing uint8
Finished bool // exposed for caller convenience. do NOT set directly.
tDelta uint32
}
// New series
func NewSeriesLong(t0 uint32) *SeriesLong {
s := SeriesLong{
T0: t0,
leading: ^uint8(0),
tDelta: 60,
}
return &s
}
// Bytes value of the series stream
func (s *SeriesLong) Bytes() []byte {
s.Lock()
defer s.Unlock()
return s.bw.bytes()
}
// Finish the series by writing an end-of-stream record
func (s *SeriesLong) Finish() {
s.Lock()
if !s.Finished {
finishV2(&s.bw)
s.Finished = true
}
s.Unlock()
}
// Push a timestamp and value to the series
func (s *SeriesLong) Push(t uint32, v float64) {
s.Lock()
defer s.Unlock()
var first bool
tDelta := t - s.T
if s.T == 0 {
first = true
tDelta = t - s.T0
}
dod := int32(tDelta - s.tDelta)
switch {
case dod == 0:
s.bw.writeBit(zero)
case -63 <= dod && dod <= 64:
s.bw.writeBits(0x02, 2) // '10'
s.bw.writeBits(uint64(dod), 7)
case -255 <= dod && dod <= 256:
s.bw.writeBits(0x06, 3) // '110'
s.bw.writeBits(uint64(dod), 9)
case -2047 <= dod && dod <= 2048:
s.bw.writeBits(0x0e, 4) // '1110'
s.bw.writeBits(uint64(dod), 12)
default:
s.bw.writeBits(0x1e, 5) // '11110'
s.bw.writeBits(uint64(dod), 32)
}
s.tDelta = tDelta
s.T = t
if first {
// first point; write full float value
s.bw.writeBits(math.Float64bits(v), 64)
s.val = v
return
}
vDelta := math.Float64bits(v) ^ math.Float64bits(s.val)
if vDelta == 0 {
s.bw.writeBit(zero)
} else {
s.bw.writeBit(one)
leading := uint8(bits.LeadingZeros64(vDelta))
trailing := uint8(bits.TrailingZeros64(vDelta))
// clamp number of leading zeros to avoid overflow when encoding
if leading >= 32 {
leading = 31
}
// TODO(dgryski): check if it's 'cheaper' to reset the leading/trailing bits instead
if s.leading != ^uint8(0) && leading >= s.leading && trailing >= s.trailing {
s.bw.writeBit(zero)
s.bw.writeBits(vDelta>>s.trailing, 64-int(s.leading)-int(s.trailing))
} else {
s.leading, s.trailing = leading, trailing
s.bw.writeBit(one)
s.bw.writeBits(uint64(leading), 5)
// Note that if leading == trailing == 0, then sigbits == 64. But that value doesn't actually fit into the 6 bits we have.
// Luckily, we never need to encode 0 significant bits, since that would put us in the other case (vdelta == 0).
// So instead we write out a 0 and adjust it back to 64 on unpacking.
sigbits := 64 - leading - trailing
s.bw.writeBits(uint64(sigbits), 6)
s.bw.writeBits(vDelta>>trailing, int(sigbits))
}
}
s.val = v
}
// IterLong lets you iterate over a series. It is not concurrency-safe.
func (s *SeriesLong) Iter() *IterLong {
s.Lock()
w := s.bw.clone()
s.Unlock()
finishV2(w)
iter, _ := bstreamIteratorLong(s.T0, w)
return iter
}
// IterLong lets you iterate over a series. It is not concurrency-safe.
type IterLong struct {
T0 uint32
t uint32
val float64
br bstream
leading uint8
trailing uint8
finished bool
tDelta uint32
err error
}
func bstreamIteratorLong(t0 uint32, br *bstream) (*IterLong, error) {
br.count = 8
return &IterLong{
T0: t0,
br: *br,
tDelta: 60,
}, nil
}
// NewIteratorLong for the series
func NewIteratorLong(t0 uint32, b []byte) (*IterLong, error) {
return bstreamIteratorLong(t0, newBReader(b))
}
func (it *IterLong) dod() (int32, bool) {
var d byte
for i := 0; i < 5; i++ {
d <<= 1
bit, err := it.br.readBit()
if err != nil {
it.err = err
return 0, false
}
if bit == zero {
break
}
d |= 1
}
var dod int32
var sz uint
switch d {
case 0x00:
// dod == 0
case 0x02: // '10'
sz = 7
case 0x06: // '110'
sz = 9
case 0x0e: // '1110'
sz = 12
case 0x1e: // '11110'
bits, err := it.br.readBits(32)
if err != nil {
it.err = err
return 0, false
}
dod = int32(bits)
case 0x1f: // '11111': end-of-stream
it.finished = true
return 0, false
}
if sz != 0 {
bits, err := it.br.readBits(int(sz))
if err != nil {
it.err = err
return 0, false
}
if bits > (1 << (sz - 1)) {
// or something
bits = bits - (1 << sz)
}
dod = int32(bits)
}
return dod, true
}
// Next iteration of the series iterator
func (it *IterLong) Next() bool {
if it.err != nil || it.finished {
return false
}
var first bool
if it.t == 0 {
it.t = it.T0
first = true
}
// read delta-of-delta
dod, ok := it.dod()
if !ok {
return false
}
it.tDelta += uint32(dod)
it.t = it.t + it.tDelta
if first {
// first point. read the float raw
v, err := it.br.readBits(64)
if err != nil {
it.err = err
return false
}
it.val = math.Float64frombits(v)
return true
}
// read compressed value
bit, err := it.br.readBit()
if err != nil {
it.err = err
return false
}
if bit == zero {
// it.val = it.val
} else {
bit, itErr := it.br.readBit()
if itErr != nil {
it.err = err
return false
}
if bit == zero {
// reuse leading/trailing zero bits
// it.leading, it.trailing = it.leading, it.trailing
} else {
bits, err := it.br.readBits(5)
if err != nil {
it.err = err
return false
}
it.leading = uint8(bits)
bits, err = it.br.readBits(6)
if err != nil {
it.err = err
return false
}
mbits := uint8(bits)
// 0 significant bits here means we overflowed and we actually need 64; see comment in encoder
if mbits == 0 {
mbits = 64
}
it.trailing = 64 - it.leading - mbits
}
mbits := int(64 - it.leading - it.trailing)
bits, err := it.br.readBits(mbits)
if err != nil {
it.err = err
return false
}
vbits := math.Float64bits(it.val)
vbits ^= (bits << it.trailing)
it.val = math.Float64frombits(vbits)
}
return true
}
// Values at the current iterator position
func (it *IterLong) Values() (uint32, float64) {
return it.t, it.val
}
// Err error at the current iterator position
func (it *IterLong) Err() error {
return it.err
}
// MarshalBinary implements the encoding.BinaryMarshaler interface
func (s *SeriesLong) MarshalBinary() ([]byte, error) {
buf := new(bytes.Buffer)
em := &errMarshal{w: buf}
em.write(s.T0)
em.write(s.leading)
em.write(s.T)
em.write(s.tDelta)
em.write(s.trailing)
em.write(s.val)
bStream, err := s.bw.MarshalBinary()
if err != nil {
return nil, err
}
em.write(bStream)
if em.err != nil {
return nil, em.err
}
return buf.Bytes(), nil
}
// UnmarshalBinary implements the encoding.BinaryUnmarshaler interface
func (s *SeriesLong) UnmarshalBinary(b []byte) error {
buf := bytes.NewReader(b)
em := &errMarshal{r: buf}
em.read(&s.T0)
em.read(&s.leading)
em.read(&s.T)
em.read(&s.tDelta)
em.read(&s.trailing)
em.read(&s.val)
outBuf := make([]byte, buf.Len())
em.read(outBuf)
err := s.bw.UnmarshalBinary(outBuf)
if err != nil {
return err
}
if em.err != nil {
return em.err
}
return nil
}