forked from gitea/gitea
94 lines
2.5 KiB
Go
94 lines
2.5 KiB
Go
|
// 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
|
||
|
}
|