added quick hash function

sneakerhash.go

@@ -1,8 +1,7 @@
 package main
 
 import (
-	"database/sql"
-    //"github.com/kalafut/imohash"
+    "database/sql"
     _ "github.com/mattn/go-sqlite3"
     "log"
     "io"
@@ -13,8 +12,26 @@ import (
     "path/filepath"
     "strconv"
     "encoding/hex"
+    "encoding/binary"
+    "hash"
+    "reflect"
 )
 
+const sampleSize = 16 * 1024
+const sampleThreshold = 48 * 1024
+
+func copyHash(src hash.Hash) hash.Hash {
+    typ := reflect.TypeOf(src)
+    val := reflect.ValueOf(src)
+    if typ.Kind() == reflect.Ptr {
+        typ = typ.Elem()
+        val = val.Elem()
+    }
+    elem := reflect.New(typ).Elem()
+    elem.Set(val)
+    return elem.Addr().Interface().(hash.Hash)
+}
+
 func hash_directory (searchDir, database string) {
 	db, dberr := sql.Open("sqlite3", database)
 	if dberr != nil {
@@ -38,10 +55,29 @@ func hash_directory (searchDir, database string) {
 				if _, err := io.Copy(h, f); err != nil {
 					log.Fatal(err)
 				}
+				qh := copyHash(h)
+				if info.Size() > int64(sampleThreshold) {
+						qh.Reset()
+						buffer := make([]byte, sampleSize)
+						f.Read(buffer)
+						qh.Write(buffer)
+						f.Seek(info.Size()/2-sampleSize/2, 0)
+						f.Read(buffer)
+						qh.Write(buffer)
+						f.Seek(int64(-sampleSize), 2)
+						f.Read(buffer)
+						qh.Write(buffer)
+				}
+				buffer := make([]byte, 8)
+				binary.PutVarint(buffer, info.Size())
+				qh.Write(buffer)
+				quickSum := hex.EncodeToString(qh.Sum(nil))
+
 				hashSum := hex.EncodeToString(h.Sum(nil))
-				fmt.Printf("SHA1: %x\n", hashSum)
-				fmt.Printf("Size: %d\n", info.Size())
-				fmt.Printf("Time: %s\n\n", info.ModTime().Format(time.RFC3339))
+				fmt.Printf("SHA1:  %x\n", hashSum)
+				fmt.Printf("qSHA1: %x\n", quickSum)
+				fmt.Printf("Size:  %d\n", info.Size())
+				fmt.Printf("Time:  %s\n\n", info.ModTime().Format(time.RFC3339))
 				sqlStatement := "INSERT INTO hashes (hash_sha1, filename, filesize_bytes, path, changedate )"+
 				"VALUES ('"+hashSum+"','"+info.Name()+"','"+strconv.FormatInt(info.Size(),10)+"','"+path+"','"+info.ModTime().Format(time.RFC3339)+"');"