1st

enc/cumdelta.go

@@ -0,0 +1,102 @@
+package enc
+
+import (
+	"math"
+
+	"gordenko.dev/dima/qb/bin"
+)
+
+type ReverseCumulativeDeltaDecompressor struct {
+	buf        []byte
+	pos        int
+	bound      int
+	firstValue float64
+	lastValue  float64
+	length     uint16
+	coef       float64
+	idxOf8     uint
+	s8         byte
+}
+
+func NewReverseCumulativeDeltaDecompressor(buf []byte, fracDigits byte) *ReverseCumulativeDeltaDecompressor {
+	var coef float64 = 1
+	if fracDigits > 0 {
+		coef = math.Pow(10, float64(fracDigits))
+	}
+	return &ReverseCumulativeDeltaDecompressor{
+		buf:  buf,
+		coef: coef,
+		pos:  len(buf),
+	}
+}
+
+func (s *ReverseCumulativeDeltaDecompressor) NextValue() (value float64, done bool) {
+	if s.length > 0 {
+		s.length--
+		return s.lastValue, false
+	}
+	if s.pos < s.bound {
+		return 0, true
+	}
+
+	if s.pos == len(s.buf) {
+		u64, n, err := bin.GetVarUint64(s.buf)
+		if err != nil {
+			panic(err)
+		}
+		s.firstValue = float64(u64) / s.coef
+		s.bound = n
+		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--
+		}
+		return s.lastValue, false
+	}
+
+	if s.idxOf8 == 0 {
+		s.s8 = s.buf[s.pos]
+		s.pos--
+	}
+	s.readVar()
+	if s.length > 0 {
+		s.length--
+	}
+	return s.lastValue, false
+}
+
+func (s *ReverseCumulativeDeltaDecompressor) readVar() {
+	u64, n, err := bin.ReverseGetVarUint64(s.buf[:s.pos+1])
+	if err != nil {
+		panic(err)
+	}
+	s.pos -= n
+	s.lastValue = s.firstValue + float64(u64)/s.coef
+
+	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 *ReverseCumulativeDeltaDecompressor) 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
+}