1 files changed, 307 insertions, 0 deletions
diff --git a/src/index/suffixarray/suffixarray.go b/src/index/suffixarray/suffixarray.go
new file mode 100644
index 000000000..c59ae6eef
--- /dev/null
+++ b/src/index/suffixarray/suffixarray.go
@@ -0,0 +1,307 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package suffixarray implements substring search in logarithmic time using
+// an in-memory suffix array.
+//
+// Example use:
+//
+//	// create index for some data
+//	index := suffixarray.New(data)
+//
+//	// lookup byte slice s
+//	offsets1 := index.Lookup(s, -1) // the list of all indices where s occurs in data
+//	offsets2 := index.Lookup(s, 3)  // the list of at most 3 indices where s occurs in data
+//
+package suffixarray
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+	"regexp"
+	"sort"
+)
+
+// Index implements a suffix array for fast substring search.
+type Index struct {
+	data []byte
+	sa   []int // suffix array for data; len(sa) == len(data)
+}
+
+// New creates a new Index for data.
+// Index creation time is O(N*log(N)) for N = len(data).
+func New(data []byte) *Index {
+	return &Index{data, qsufsort(data)}
+}
+
+// writeInt writes an int x to w using buf to buffer the write.
+func writeInt(w io.Writer, buf []byte, x int) error {
+	binary.PutVarint(buf, int64(x))
+	_, err := w.Write(buf[0:binary.MaxVarintLen64])
+	return err
+}
+
+// readInt reads an int x from r using buf to buffer the read and returns x.
+func readInt(r io.Reader, buf []byte) (int, error) {
+	_, err := io.ReadFull(r, buf[0:binary.MaxVarintLen64]) // ok to continue with error
+	x, _ := binary.Varint(buf)
+	return int(x), err
+}
+
+// writeSlice writes data[:n] to w and returns n.
+// It uses buf to buffer the write.
+func writeSlice(w io.Writer, buf []byte, data []int) (n int, err error) {
+	// encode as many elements as fit into buf
+	p := binary.MaxVarintLen64
+	for ; n < len(data) && p+binary.MaxVarintLen64 <= len(buf); n++ {
+		p += binary.PutUvarint(buf[p:], uint64(data[n]))
+	}
+
+	// update buffer size
+	binary.PutVarint(buf, int64(p))
+
+	// write buffer
+	_, err = w.Write(buf[0:p])
+	return
+}
+
+// readSlice reads data[:n] from r and returns n.
+// It uses buf to buffer the read.
+func readSlice(r io.Reader, buf []byte, data []int) (n int, err error) {
+	// read buffer size
+	var size int
+	size, err = readInt(r, buf)
+	if err != nil {
+		return
+	}
+
+	// read buffer w/o the size
+	if _, err = io.ReadFull(r, buf[binary.MaxVarintLen64:size]); err != nil {
+		return
+	}
+
+	// decode as many elements as present in buf
+	for p := binary.MaxVarintLen64; p < size; n++ {
+		x, w := binary.Uvarint(buf[p:])
+		data[n] = int(x)
+		p += w
+	}
+
+	return
+}
+
+const bufSize = 16 << 10 // reasonable for BenchmarkSaveRestore
+
+// Read reads the index from r into x; x must not be nil.
+func (x *Index) Read(r io.Reader) error {
+	// buffer for all reads
+	buf := make([]byte, bufSize)
+
+	// read length
+	n, err := readInt(r, buf)
+	if err != nil {
+		return err
+	}
+
+	// allocate space
+	if 2*n < cap(x.data) || cap(x.data) < n {
+		// new data is significantly smaller or larger then
+		// existing buffers - allocate new ones
+		x.data = make([]byte, n)
+		x.sa = make([]int, n)
+	} else {
+		// re-use existing buffers
+		x.data = x.data[0:n]
+		x.sa = x.sa[0:n]
+	}
+
+	// read data
+	if _, err := io.ReadFull(r, x.data); err != nil {
+		return err
+	}
+
+	// read index
+	for sa := x.sa; len(sa) > 0; {
+		n, err := readSlice(r, buf, sa)
+		if err != nil {
+			return err
+		}
+		sa = sa[n:]
+	}
+	return nil
+}
+
+// Write writes the index x to w.
+func (x *Index) Write(w io.Writer) error {
+	// buffer for all writes
+	buf := make([]byte, bufSize)
+
+	// write length
+	if err := writeInt(w, buf, len(x.data)); err != nil {
+		return err
+	}
+
+	// write data
+	if _, err := w.Write(x.data); err != nil {
+		return err
+	}
+
+	// write index
+	for sa := x.sa; len(sa) > 0; {
+		n, err := writeSlice(w, buf, sa)
+		if err != nil {
+			return err
+		}
+		sa = sa[n:]
+	}
+	return nil
+}
+
+// Bytes returns the data over which the index was created.
+// It must not be modified.
+//
+func (x *Index) Bytes() []byte {
+	return x.data
+}
+
+func (x *Index) at(i int) []byte {
+	return x.data[x.sa[i]:]
+}
+
+// lookupAll returns a slice into the matching region of the index.
+// The runtime is O(log(N)*len(s)).
+func (x *Index) lookupAll(s []byte) []int {
+	// find matching suffix index range [i:j]
+	// find the first index where s would be the prefix
+	i := sort.Search(len(x.sa), func(i int) bool { return bytes.Compare(x.at(i), s) >= 0 })
+	// starting at i, find the first index at which s is not a prefix
+	j := i + sort.Search(len(x.sa)-i, func(j int) bool { return !bytes.HasPrefix(x.at(j+i), s) })
+	return x.sa[i:j]
+}
+
+// Lookup returns an unsorted list of at most n indices where the byte string s
+// occurs in the indexed data. If n < 0, all occurrences are returned.
+// The result is nil if s is empty, s is not found, or n == 0.
+// Lookup time is O(log(N)*len(s) + len(result)) where N is the
+// size of the indexed data.
+//
+func (x *Index) Lookup(s []byte, n int) (result []int) {
+	if len(s) > 0 && n != 0 {
+		matches := x.lookupAll(s)
+		if n < 0 || len(matches) < n {
+			n = len(matches)
+		}
+		// 0 <= n <= len(matches)
+		if n > 0 {
+			result = make([]int, n)
+			copy(result, matches)
+		}
+	}
+	return
+}
+
+// FindAllIndex returns a sorted list of non-overlapping matches of the
+// regular expression r, where a match is a pair of indices specifying
+// the matched slice of x.Bytes(). If n < 0, all matches are returned
+// in successive order. Otherwise, at most n matches are returned and
+// they may not be successive. The result is nil if there are no matches,
+// or if n == 0.
+//
+func (x *Index) FindAllIndex(r *regexp.Regexp, n int) (result [][]int) {
+	// a non-empty literal prefix is used to determine possible
+	// match start indices with Lookup
+	prefix, complete := r.LiteralPrefix()
+	lit := []byte(prefix)
+
+	// worst-case scenario: no literal prefix
+	if prefix == "" {
+		return r.FindAllIndex(x.data, n)
+	}
+
+	// if regexp is a literal just use Lookup and convert its
+	// result into match pairs
+	if complete {
+		// Lookup returns indices that may belong to overlapping matches.
+		// After eliminating them, we may end up with fewer than n matches.
+		// If we don't have enough at the end, redo the search with an
+		// increased value n1, but only if Lookup returned all the requested
+		// indices in the first place (if it returned fewer than that then
+		// there cannot be more).
+		for n1 := n; ; n1 += 2 * (n - len(result)) /* overflow ok */ {
+			indices := x.Lookup(lit, n1)
+			if len(indices) == 0 {
+				return
+			}
+			sort.Ints(indices)
+			pairs := make([]int, 2*len(indices))
+			result = make([][]int, len(indices))
+			count := 0
+			prev := 0
+			for _, i := range indices {
+				if count == n {
+					break
+				}
+				// ignore indices leading to overlapping matches
+				if prev <= i {
+					j := 2 * count
+					pairs[j+0] = i
+					pairs[j+1] = i + len(lit)
+					result[count] = pairs[j : j+2]
+					count++
+					prev = i + len(lit)
+				}
+			}
+			result = result[0:count]
+			if len(result) >= n || len(indices) != n1 {
+				// found all matches or there's no chance to find more
+				// (n and n1 can be negative)
+				break
+			}
+		}
+		if len(result) == 0 {
+			result = nil
+		}
+		return
+	}
+
+	// regexp has a non-empty literal prefix; Lookup(lit) computes
+	// the indices of possible complete matches; use these as starting
+	// points for anchored searches
+	// (regexp "^" matches beginning of input, not beginning of line)
+	r = regexp.MustCompile("^" + r.String()) // compiles because r compiled
+
+	// same comment about Lookup applies here as in the loop above
+	for n1 := n; ; n1 += 2 * (n - len(result)) /* overflow ok */ {
+		indices := x.Lookup(lit, n1)
+		if len(indices) == 0 {
+			return
+		}
+		sort.Ints(indices)
+		result = result[0:0]
+		prev := 0
+		for _, i := range indices {
+			if len(result) == n {
+				break
+			}
+			m := r.FindIndex(x.data[i:]) // anchored search - will not run off
+			// ignore indices leading to overlapping matches
+			if m != nil && prev <= i {
+				m[0] = i // correct m
+				m[1] += i
+				result = append(result, m)
+				prev = m[1]
+			}
+		}
+		if len(result) >= n || len(indices) != n1 {
+			// found all matches or there's no chance to find more
+			// (n and n1 can be negative)
+			break
+		}
+	}
+	if len(result) == 0 {
+		result = nil
+	}
+	return
+}