add findSimilarChunks method to test sketches

Still missing a real test...

1 files changed, 12 insertions, 4 deletions

diff --git a/sketch.go b/sketch.go
index c5f0838..f226661 100644
--- a/sketch.go
+++ b/sketch.go
@@ -3,18 +3,23 @@ package main
 import (
 	"encoding/binary"
 	"io"
+	"log"
 
 	"github.com/chmduquesne/rollinghash/rabinkarp64"
 )
 
+type Sketch []uint64
+
+const fBytes = 8
+
 // SketchChunk produces a sketch for a chunk based on wSize: the window size,
 // sfCount: the number of super-features, and fCount: the number of feature
 // per super-feature
-func SketchChunk(chunk Chunk, wSize int, sfCount int, fCount int) ([]uint64, error) {
+func SketchChunk(chunk Chunk, wSize int, sfCount int, fCount int) (Sketch, error) {
 	var fSize = chunkSize / (sfCount * fCount)
 	superfeatures := make([]uint64, 0, sfCount)
 	features := make([]uint64, 0, fCount)
-	buff := make([]byte, 8*fCount)
+	buff := make([]byte, fBytes*fCount)
 	r, err := chunk.Reader()
 	if err != nil {
 		return nil, err
@@ -24,7 +29,10 @@ func SketchChunk(chunk Chunk, wSize int, sfCount int, fCount int) ([]uint64, err
 		features = features[:0]
 		for f := 0; f < fCount; f++ {
 			hasher.Reset()
-			io.CopyN(hasher, r, int64(wSize))
+			n, err := io.CopyN(hasher, r, int64(wSize))
+			if err != nil {
+				log.Println(n, err)
+			}
 			max := hasher.Sum64()
 			for w := 0; w < fSize-wSize; w++ {
 				b, _ := r.ReadByte()
@@ -37,7 +45,7 @@ func SketchChunk(chunk Chunk, wSize int, sfCount int, fCount int) ([]uint64, err
 			features = append(features, max)
 		}
 		for i, f := range features {
-			binary.LittleEndian.PutUint64(buff[i*8:i*8+8], f)
+			binary.LittleEndian.PutUint64(buff[i*fBytes:(i+1)*fBytes], f)
 		}
 		hasher.Reset()
 		hasher.Write(buff)