1st

enc/time_delta_delta.go

@@ -0,0 +1,145 @@
+package enc
+
+import (
+	"gordenko.dev/dima/qb/bin"
+)
+
+// REVERSE
+
+const (
+	lastUnixtimeIdx = 0
+	baseDeltaIdx    = 4
+)
+
+type ReverseTimeDeltaOfDeltaDecompressor struct {
+	step             byte
+	buf              []byte
+	pos              int
+	bound            int
+	lastUnixtime     uint32
+	baseDelta        uint32
+	lastDeltaOfDelta int64
+	length           uint16
+	idxOf8           uint
+	s8               byte
+}
+
+func NewReverseTimeDeltaOfDeltaDecompressor(buf []byte) *ReverseTimeDeltaOfDeltaDecompressor {
+	return &ReverseTimeDeltaOfDeltaDecompressor{
+		buf: buf,
+		pos: len(buf),
+	}
+}
+
+func (s *ReverseTimeDeltaOfDeltaDecompressor) NextValue() (value uint32, done bool) {
+	if s.step == 0 {
+		if s.pos == 0 {
+			return 0, true
+		}
+		s.lastUnixtime = bin.GetUint32(s.buf[lastUnixtimeIdx:])
+		s.step = 1
+		return s.lastUnixtime, false
+	}
+
+	if s.step == 1 {
+		if s.pos == baseDeltaIdx {
+			return 0, true
+		}
+		u64, n, err := bin.GetVarUint64(s.buf[baseDeltaIdx:])
+		if err != nil {
+			panic("EOF")
+		}
+		s.bound = baseDeltaIdx + n
+		s.baseDelta = uint32(u64)
+
+		s.pos--
+		s.idxOf8 = uint(8 - s.buf[s.pos])
+		s.pos--
+		s.s8 = s.buf[s.pos]
+		s.pos--
+
+		s.readVar()
+		if s.length > 0 {
+			s.length--
+		}
+		s.step = 2
+		return s.lastUnixtime, false
+	}
+
+	if s.length > 0 {
+		s.length--
+		delta := int64(s.baseDelta) + s.lastDeltaOfDelta
+		s.lastUnixtime = uint32(int64(s.lastUnixtime) - delta)
+		return s.lastUnixtime, false
+	}
+
+	if s.pos < s.bound {
+		return 0, true
+	}
+	if s.idxOf8 == 0 {
+		s.s8 = s.buf[s.pos]
+		s.pos--
+	}
+	s.readVar()
+	if s.length > 0 {
+		s.length--
+	}
+	return s.lastUnixtime, false
+}
+
+func GetTimeRange(timestampsBuf []byte) (since, until uint32) {
+	decompressor := NewReverseTimeDeltaOfDeltaDecompressor(timestampsBuf)
+	value, done := decompressor.NextValue()
+	if done {
+		return
+	}
+
+	since = value
+	until = value
+	for {
+		value, done = decompressor.NextValue()
+		if done {
+			return
+		}
+		since = value
+	}
+}
+
+func (s *ReverseTimeDeltaOfDeltaDecompressor) readVar() {
+	var (
+		n   int
+		err error
+	)
+
+	s.lastDeltaOfDelta, n, err = bin.ReverseGetVarInt64(s.buf[:s.pos+1])
+	if err != nil {
+		panic(err)
+	}
+	s.pos -= n
+
+	delta := int64(s.baseDelta) + s.lastDeltaOfDelta
+	s.lastUnixtime = uint32(int64(s.lastUnixtime) - delta)
+
+	var flag byte = 1 << s.idxOf8
+	if (s.s8 & flag) == flag {
+		s.decodeLength()
+	}
+	if s.idxOf8 == 7 {
+		s.idxOf8 = 0
+	} else {
+		s.idxOf8++
+	}
+}
+
+func (s *ReverseTimeDeltaOfDeltaDecompressor) decodeLength() {
+	b1 := s.buf[s.pos]
+	s.pos--
+	if b1 < 128 {
+		s.length = uint16(b1)
+	} else {
+		b2 := s.buf[s.pos]
+		s.pos--
+		s.length = uint16(b1&127) | (uint16(b2) << 7)
+	}
+	s.length += 2
+}