Support common initialisms

da.go

@@ -0,0 +1,236 @@
+package stringutil
+
+import (
+	"fmt"
+	"sort"
+	"unicode/utf8"
+)
+
+const (
+	terminationCharacter = '#'
+)
+
+func mustDoubleArray(da *doubleArray, err error) *doubleArray {
+	if err != nil {
+		panic(err)
+	}
+	return da
+}
+
+func (da *doubleArray) Build(keys []string) error {
+	records := makeRecords(keys)
+	if err := da.build(records, 1, 0, make(map[int]struct{})); err != nil {
+		return err
+	}
+	return nil
+}
+
+type doubleArray struct {
+	bc   []baseCheck
+	node []int
+}
+
+func newDoubleArray(keys []string) (*doubleArray, error) {
+	da := &doubleArray{
+		bc:   []baseCheck{0},
+		node: []int{-1}, // A start index is adjusting to 1 because 0 will be used as a mark of non-existent node.
+	}
+	if err := da.Build(keys); err != nil {
+		return nil, err
+	}
+	return da, nil
+}
+
+// baseCheck contains BASE, CHECK and Extra flags.
+// From the top, 22bits of BASE, 2bits of Extra flags and 8bits of CHECK.
+//
+//  BASE (22bit) | Extra flags (2bit) | CHECK (8bit)
+// |----------------------|--|--------|
+// 32                    10  8         0
+type baseCheck uint32
+
+func (bc baseCheck) Base() int {
+	return int(bc >> 10)
+}
+
+func (bc *baseCheck) SetBase(base int) {
+	*bc |= baseCheck(base) << 10
+}
+
+func (bc baseCheck) Check() byte {
+	return byte(bc)
+}
+
+func (bc *baseCheck) SetCheck(check byte) {
+	*bc |= baseCheck(check)
+}
+
+func (bc baseCheck) IsEmpty() bool {
+	return bc&0xfffffcff == 0
+}
+
+func (da *doubleArray) Lookup(path string) (length int) {
+	idx := 1
+	tmpIdx := idx
+	for i := 0; i < len(path); i++ {
+		c := path[i]
+		tmpIdx = da.nextIndex(da.bc[tmpIdx].Base(), c)
+		if tmpIdx >= len(da.bc) || da.bc[tmpIdx].Check() != c {
+			break
+		}
+		idx = tmpIdx
+	}
+	if next := da.nextIndex(da.bc[idx].Base(), terminationCharacter); next < len(da.bc) && da.bc[next].Check() == terminationCharacter {
+		return da.node[da.bc[next].Base()]
+	}
+	return -1
+}
+
+func (da *doubleArray) build(srcs []record, idx, depth int, usedBase map[int]struct{}) error {
+	sort.Stable(recordSlice(srcs))
+	base, siblings, leaf, err := da.arrange(srcs, idx, depth, usedBase)
+	if err != nil {
+		return err
+	}
+	if leaf != nil {
+		da.bc[idx].SetBase(len(da.node))
+		da.node = append(da.node, leaf.value)
+	}
+	for _, sib := range siblings {
+		da.setCheck(da.nextIndex(base, sib.c), sib.c)
+	}
+	for _, sib := range siblings {
+		if err := da.build(srcs[sib.start:sib.end], da.nextIndex(base, sib.c), depth+1, usedBase); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (da *doubleArray) setBase(i, base int) {
+	da.bc[i].SetBase(base)
+}
+
+func (da *doubleArray) setCheck(i int, check byte) {
+	da.bc[i].SetCheck(check)
+}
+
+func (da *doubleArray) findEmptyIndex(start int) int {
+	i := start
+	for ; i < len(da.bc); i++ {
+		if da.bc[i].IsEmpty() {
+			break
+		}
+	}
+	return i
+}
+
+// findBase returns good BASE.
+func (da *doubleArray) findBase(siblings []sibling, start int, usedBase map[int]struct{}) (base int) {
+	for idx, firstChar := start+1, siblings[0].c; ; idx = da.findEmptyIndex(idx + 1) {
+		base = da.nextIndex(idx, firstChar)
+		if _, used := usedBase[base]; used {
+			continue
+		}
+		i := 0
+		for ; i < len(siblings); i++ {
+			next := da.nextIndex(base, siblings[i].c)
+			if len(da.bc) <= next {
+				da.bc = append(da.bc, make([]baseCheck, next-len(da.bc)+1)...)
+			}
+			if !da.bc[next].IsEmpty() {
+				break
+			}
+		}
+		if i == len(siblings) {
+			break
+		}
+	}
+	usedBase[base] = struct{}{}
+	return base
+}
+
+func (da *doubleArray) arrange(records []record, idx, depth int, usedBase map[int]struct{}) (base int, siblings []sibling, leaf *record, err error) {
+	siblings, leaf, err = makeSiblings(records, depth)
+	if err != nil {
+		return -1, nil, nil, err
+	}
+	if len(siblings) < 1 {
+		return -1, nil, leaf, nil
+	}
+	base = da.findBase(siblings, idx, usedBase)
+	da.setBase(idx, base)
+	return base, siblings, leaf, err
+}
+
+type sibling struct {
+	start int
+	end   int
+	c     byte
+}
+
+func (da *doubleArray) nextIndex(base int, c byte) int {
+	return base ^ int(c)
+}
+
+func makeSiblings(records []record, depth int) (sib []sibling, leaf *record, err error) {
+	var (
+		pc byte
+		n  int
+	)
+	for i, r := range records {
+		if len(r.key) <= depth {
+			leaf = &r
+			continue
+		}
+		c := r.key[depth]
+		switch {
+		case pc < c:
+			sib = append(sib, sibling{start: i, c: c})
+		case pc == c:
+			continue
+		default:
+			return nil, nil, fmt.Errorf("stringutil: BUG: records hasn't been sorted")
+		}
+		if n > 0 {
+			sib[n-1].end = i
+		}
+		pc = c
+		n++
+	}
+	if n == 0 {
+		return nil, leaf, nil
+	}
+	sib[n-1].end = len(records)
+	return sib, leaf, nil
+}
+
+type record struct {
+	key   string
+	value int
+}
+
+func makeRecords(srcs []string) (records []record) {
+	termChar := string(terminationCharacter)
+	for _, s := range srcs {
+		records = append(records, record{
+			key:   string(s + termChar),
+			value: utf8.RuneCountInString(s),
+		})
+	}
+	return records
+}
+
+type recordSlice []record
+
+func (rs recordSlice) Len() int {
+	return len(rs)
+}
+
+func (rs recordSlice) Less(i, j int) bool {
+	return rs[i].key < rs[j].key
+}
+
+func (rs recordSlice) Swap(i, j int) {
+	rs[i], rs[j] = rs[j], rs[i]
+}