index/suffixarray: support for serialization

R=r
CC=golang-dev
https://golang.org/cl/5040041

1 files changed, 52 insertions, 4 deletions

diff --git a/src/pkg/index/suffixarray/suffixarray.go b/src/pkg/index/suffixarray/suffixarray.go
index c78de854de..c2a999483b 100644
--- a/src/pkg/index/suffixarray/suffixarray.go
+++ b/src/pkg/index/suffixarray/suffixarray.go
@@ -18,14 +18,17 @@ package suffixarray
 
 import (
 	"bytes"
+	"encoding/binary"
 	"exp/regexp"
+	"io"
+	"os"
 	"sort"
 )
 
 // Index implements a suffix array for fast substring search.
 type Index struct {
 	data []byte
-	sa   []int // suffix array for data
+	sa   []int32 // suffix array for data; len(sa) == len(data)
 }
 
 // New creates a new Index for data.
@@ -34,6 +37,48 @@ func New(data []byte) *Index {
 	return &Index{data, qsufsort(data)}
 }
 
+// Read reads the index from r into x; x must not be nil.
+func (x *Index) Read(r io.Reader) os.Error {
+	var n int32
+	if err := binary.Read(r, binary.LittleEndian, &n); err != nil {
+		return err
+	}
+	if 2*n < int32(cap(x.data)) || int32(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([]int32, n)
+	} else {
+		// re-use existing buffers
+		x.data = x.data[0:n]
+		x.sa = x.sa[0:n]
+	}
+
+	if err := binary.Read(r, binary.LittleEndian, x.data); err != nil {
+		return err
+	}
+	if err := binary.Read(r, binary.LittleEndian, x.sa); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+// Write writes the index x to w.
+func (x *Index) Write(w io.Writer) os.Error {
+	n := int32(len(x.data))
+	if err := binary.Write(w, binary.LittleEndian, n); err != nil {
+		return err
+	}
+	if err := binary.Write(w, binary.LittleEndian, x.data); err != nil {
+		return err
+	}
+	if err := binary.Write(w, binary.LittleEndian, x.sa); err != nil {
+		return err
+	}
+	return nil
+}
+
 // Bytes returns the data over which the index was created.
 // It must not be modified.
 //
@@ -47,7 +92,7 @@ func (x *Index) at(i int) []byte {
 
 // 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 {
+func (x *Index) lookupAll(s []byte) []int32 {
 	// 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 })
@@ -65,12 +110,15 @@ func (x *Index) lookupAll(s []byte) []int {
 func (x *Index) Lookup(s []byte, n int) (result []int) {
 	if len(s) > 0 && n != 0 {
 		matches := x.lookupAll(s)
-		if len(matches) < n || n < 0 {
+		if n < 0 || len(matches) < n {
 			n = len(matches)
 		}
+		// 0 <= n <= len(matches)
 		if n > 0 {
 			result = make([]int, n)
-			copy(result, matches)
+			for i, x := range matches[0:n] {
+				result[i] = int(x)
+			}
 		}
 	}
 	return