Vendor used libs

vendor/github.com/dsnet/compress/internal/prefix/range.go

@@ -0,0 +1,93 @@
+// Copyright 2015, Joe Tsai. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE.md file.
+
+package prefix
+
+type RangeCode struct {
+	Base uint32 // Starting base offset of the range
+	Len  uint32 // Bit-length of a subsequent integer to add to base offset
+}
+type RangeCodes []RangeCode
+
+type RangeEncoder struct {
+	rcs     RangeCodes
+	lut     [1024]uint32
+	minBase uint
+}
+
+// End reports the non-inclusive ending range.
+func (rc RangeCode) End() uint32 { return rc.Base + (1 << rc.Len) }
+
+// MakeRangeCodes creates a RangeCodes, where each region is assumed to be
+// contiguously stacked, without any gaps, with bit-lengths taken from bits.
+func MakeRangeCodes(minBase uint, bits []uint) (rc RangeCodes) {
+	for _, nb := range bits {
+		rc = append(rc, RangeCode{Base: uint32(minBase), Len: uint32(nb)})
+		minBase += 1 << nb
+	}
+	return rc
+}
+
+// Base reports the inclusive starting range for all ranges.
+func (rcs RangeCodes) Base() uint32 { return rcs[0].Base }
+
+// End reports the non-inclusive ending range for all ranges.
+func (rcs RangeCodes) End() uint32 { return rcs[len(rcs)-1].End() }
+
+// checkValid reports whether the RangeCodes is valid. In order to be valid,
+// the following must hold true:
+//	rcs[i-1].Base <= rcs[i].Base
+//	rcs[i-1].End  <= rcs[i].End
+//	rcs[i-1].End  >= rcs[i].Base
+//
+// Practically speaking, each range must be increasing and must not have any
+// gaps in between. It is okay for ranges to overlap.
+func (rcs RangeCodes) checkValid() bool {
+	if len(rcs) == 0 {
+		return false
+	}
+	pre := rcs[0]
+	for _, cur := range rcs[1:] {
+		preBase, preEnd := pre.Base, pre.End()
+		curBase, curEnd := cur.Base, cur.End()
+		if preBase > curBase || preEnd > curEnd || preEnd < curBase {
+			return false
+		}
+		pre = cur
+	}
+	return true
+}
+
+func (re *RangeEncoder) Init(rcs RangeCodes) {
+	if !rcs.checkValid() {
+		panic("invalid range codes")
+	}
+	*re = RangeEncoder{rcs: rcs, minBase: uint(rcs.Base())}
+	for sym, rc := range rcs {
+		base := int(rc.Base) - int(re.minBase)
+		end := int(rc.End()) - int(re.minBase)
+		if base >= len(re.lut) {
+			break
+		}
+		if end > len(re.lut) {
+			end = len(re.lut)
+		}
+		for i := base; i < end; i++ {
+			re.lut[i] = uint32(sym)
+		}
+	}
+}
+
+func (re *RangeEncoder) Encode(offset uint) (sym uint) {
+	if idx := int(offset - re.minBase); idx < len(re.lut) {
+		return uint(re.lut[idx])
+	}
+	sym = uint(re.lut[len(re.lut)-1])
+retry:
+	if int(sym) >= len(re.rcs) || re.rcs[sym].Base > uint32(offset) {
+		return sym - 1
+	}
+	sym++
+	goto retry // Avoid for-loop so that this function can be inlined
+}