diff --git a/.github/workflows/go.yml b/.github/workflows/go.yml
index e61af21..99b495e 100644
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -12,7 +12,10 @@ on:
 jobs:
 
   build:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, windows-latest, macos-latest]
     steps:
     - name: Checkout
       uses: actions/checkout@v4
@@ -20,7 +23,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v5
       with:
-        go-version: '1.20'
+        go-version: '1.20.x'
 
     - name: Build utilities
       run: |
diff --git a/cmd/build/build.go b/cmd/build/build.go
index d97d46c..2f6f3b0 100644
--- a/cmd/build/build.go
+++ b/cmd/build/build.go
@@ -4,13 +4,13 @@ import (
 	"log"
 	"os"
 
-	"github.com/schwarzlichtbezirk/wpk"
 	lw "github.com/schwarzlichtbezirk/wpk/luawpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 func main() {
 	for _, fpath := range os.Args[1:] {
-		if err := lw.RunLuaVM(wpk.Envfmt(fpath, nil)); err != nil {
+		if err := lw.RunLuaVM(util.Envfmt(fpath, nil)); err != nil {
 			log.Println(err.Error())
 			return
 		}
diff --git a/cmd/extract/extract.go b/cmd/extract/extract.go
index 2b9d85b..84d5519 100644
--- a/cmd/extract/extract.go
+++ b/cmd/extract/extract.go
@@ -13,6 +13,7 @@ import (
 	"github.com/schwarzlichtbezirk/wpk/bulk"
 	"github.com/schwarzlichtbezirk/wpk/fsys"
 	"github.com/schwarzlichtbezirk/wpk/mmap"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // command line settings
@@ -49,7 +50,7 @@ func checkargs() int {
 		if fpath == "" {
 			continue
 		}
-		fpath = wpk.ToSlash(wpk.Envfmt(fpath, nil))
+		fpath = util.ToSlash(util.Envfmt(fpath, nil))
 		if ok, _ := wpk.FileExists(fpath); !ok {
 			log.Printf("source file #%d '%s' does not exist", i+1, fpath)
 			ec++
@@ -62,7 +63,7 @@ func checkargs() int {
 		ec++
 	}
 
-	DstPath = wpk.ToSlash(wpk.Envfmt(DstPath, nil))
+	DstPath = util.ToSlash(util.Envfmt(DstPath, nil))
 	if DstPath == "" {
 		log.Println("destination path does not specified")
 		ec++
@@ -133,7 +134,7 @@ func readpackage() (err error) {
 					next = err == nil
 				}()
 
-				var fullpath = wpk.JoinPath(DstPath, fkey)
+				var fullpath = util.JoinPath(DstPath, fkey)
 				if err = os.MkdirAll(path.Dir(fullpath), os.ModePerm); err != nil {
 					return
 				}
diff --git a/cmd/pack/pack.go b/cmd/pack/pack.go
index da51446..ed3d4c2 100644
--- a/cmd/pack/pack.go
+++ b/cmd/pack/pack.go
@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	"github.com/schwarzlichtbezirk/wpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // command line settings
@@ -41,7 +42,7 @@ func checkargs() (ec int) { // returns error counter
 		if fpath == "" {
 			continue
 		}
-		fpath = wpk.ToSlash(wpk.Envfmt(fpath, nil))
+		fpath = util.ToSlash(util.Envfmt(fpath, nil))
 		if !strings.HasSuffix(fpath, "/") {
 			fpath += "/"
 		}
@@ -57,7 +58,7 @@ func checkargs() (ec int) { // returns error counter
 		ec++
 	}
 
-	DstFile = wpk.ToSlash(wpk.Envfmt(DstFile, nil))
+	DstFile = util.ToSlash(util.Envfmt(DstFile, nil))
 	if DstFile == "" {
 		log.Println("destination file does not specified")
 		ec++
@@ -118,7 +119,7 @@ func writepackage() (err error) {
 				return nil // file is directory
 			}
 
-			var fpath = wpk.JoinPath(srcpath, fkey)
+			var fpath = util.JoinPath(srcpath, fkey)
 			var file wpk.RFile
 			var ts wpk.TagsetRaw
 			if file, err = os.Open(fpath); err != nil {
diff --git a/dir.go b/dir.go
index 26538a9..bb0c918 100644
--- a/dir.go
+++ b/dir.go
@@ -7,6 +7,8 @@ import (
 	"os"
 	"path"
 	"strings"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // MakeTagsPath receives file path and returns it with ".wpt" extension.
@@ -76,13 +78,13 @@ func FileExists(fpath string) (bool, error) {
 
 // TempPath returns filename located at temporary directory.
 func TempPath(fname string) string {
-	return JoinPath(ToSlash(os.TempDir()), fname)
+	return util.JoinPath(util.ToSlash(os.TempDir()), fname)
 }
 
 // ReadDirN returns fs.DirEntry array with nested into given package directory presentation.
 // It's core function for ReadDirFile and ReadDirFS structures.
 func (ftt *FTT) ReadDirN(fulldir string, n int) (list []fs.DirEntry, err error) {
-	fulldir = ToSlash(fulldir)
+	fulldir = util.ToSlash(fulldir)
 	var found = map[string]fs.DirEntry{}
 	var prefix string
 	if fulldir != "." && fulldir != "" {
@@ -97,7 +99,7 @@ func (ftt *FTT) ReadDirN(fulldir string, n int) (list []fs.DirEntry, err error)
 				found[suffix] = ts
 				n--
 			} else { // dir detected
-				var subdir = JoinPath(prefix, suffix[:sp])
+				var subdir = util.JoinPath(prefix, suffix[:sp])
 				if _, ok := found[subdir]; !ok {
 					var dts = TagsetRaw{}.
 						Put(TIDpath, StrTag(subdir))
@@ -128,7 +130,7 @@ func (ftt *FTT) ReadDirN(fulldir string, n int) (list []fs.DirEntry, err error)
 // OpenDir returns PackDirFile structure associated with group of files in package
 // pooled with common directory prefix. Usable to implement fs.FileSystem interface.
 func (ftt *FTT) OpenDir(fulldir string) (fs.ReadDirFile, error) {
-	fulldir = ToSlash(fulldir)
+	fulldir = util.ToSlash(fulldir)
 	var prefix string
 	if fulldir != "." && fulldir != "" {
 		prefix = fulldir + "/" // set terminated slash
diff --git a/go.mod b/go.mod
index 5072a1c..475cdbf 100644
--- a/go.mod
+++ b/go.mod
@@ -3,7 +3,7 @@ module github.com/schwarzlichtbezirk/wpk
 go 1.20
 
 require (
-	github.com/edsrzf/mmap-go v1.1.0
+	github.com/edsrzf/mmap-go v1.2.0
 	github.com/h2non/filetype v1.1.3
 	github.com/yuin/gopher-lua v1.1.1
 	gopkg.in/djherbis/times.v1 v1.3.0
diff --git a/go.sum b/go.sum
index a4f45cb..7e16fe2 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,5 @@
-github.com/edsrzf/mmap-go v1.1.0 h1:6EUwBLQ/Mcr1EYLE4Tn1VdW1A4ckqCQWZBw8Hr0kjpQ=
-github.com/edsrzf/mmap-go v1.1.0/go.mod h1:19H/e8pUPLicwkyNgOykDXkJ9F0MHE+Z52B8EIth78Q=
+github.com/edsrzf/mmap-go v1.2.0 h1:hXLYlkbaPzt1SaQk+anYwKSRNhufIDCchSPkUD6dD84=
+github.com/edsrzf/mmap-go v1.2.0/go.mod h1:19H/e8pUPLicwkyNgOykDXkJ9F0MHE+Z52B8EIth78Q=
 github.com/h2non/filetype v1.1.3 h1:FKkx9QbD7HR/zjK1Ia5XiBsq9zdLi5Kf3zGyFTAFkGg=
 github.com/h2non/filetype v1.1.3/go.mod h1:319b3zT68BvV+WRj7cwy856M2ehB3HqNOt6sy1HndBY=
 github.com/yuin/gopher-lua v1.1.1 h1:kYKnWBjvbNP4XLT3+bPEwAXJx262OhaHDWDVOPjL46M=
diff --git a/luawpk/adjusttags.go b/luawpk/adjusttags.go
index 8067ab7..e716808 100644
--- a/luawpk/adjusttags.go
+++ b/luawpk/adjusttags.go
@@ -13,7 +13,9 @@ import (
 	"path"
 
 	"github.com/h2non/filetype"
+
 	"github.com/schwarzlichtbezirk/wpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 func adjustmime(ts wpk.TagsetRaw, r io.ReadSeeker, skip bool) (wpk.TagsetRaw, error) {
@@ -22,7 +24,7 @@ func adjustmime(ts wpk.TagsetRaw, r io.ReadSeeker, skip bool) (wpk.TagsetRaw, er
 	if skip || ts.Has(wpk.TIDmime) {
 		return ts, err
 	}
-	var ext = wpk.ToLower(path.Ext(ts.Path()))
+	var ext = util.ToLower(path.Ext(ts.Path()))
 	var ctype string
 	if ctype = mime.TypeByExtension(ext); ctype == "" {
 		if ctype, ok = MimeExt[ext]; !ok {
diff --git a/luawpk/luapath.go b/luawpk/luapath.go
index 238bed1..ae9f989 100644
--- a/luawpk/luapath.go
+++ b/luawpk/luapath.go
@@ -5,8 +5,9 @@ import (
 	"path"
 	"path/filepath"
 
-	"github.com/schwarzlichtbezirk/wpk"
 	lua "github.com/yuin/gopher-lua"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // RegPath registers "path" namespace into Lua virtual machine.
@@ -34,7 +35,7 @@ var pathfuncs = map[string]lua.LGFunction{
 func pathtoslash(ls *lua.LState) int {
 	var fpath = ls.CheckString(1)
 
-	ls.Push(lua.LString(wpk.ToSlash(fpath)))
+	ls.Push(lua.LString(util.ToSlash(fpath)))
 	return 1
 }
 
@@ -73,7 +74,7 @@ func pathbase(ls *lua.LState) int {
 func pathname(ls *lua.LState) int {
 	var fpath = ls.CheckString(1)
 
-	var name = wpk.PathName(fpath)
+	var name = util.PathName(fpath)
 	ls.Push(lua.LString(name))
 	return 1
 }
@@ -128,7 +129,7 @@ func pathglob(ls *lua.LState) int {
 		return 0
 	}
 	for _, dir := range matches {
-		ls.Push(lua.LString(wpk.ToSlash(dir)))
+		ls.Push(lua.LString(util.ToSlash(dir)))
 	}
 	return len(matches)
 }
@@ -160,7 +161,7 @@ func pathenum(ls *lua.LState) int {
 
 func pathenvfmt(ls *lua.LState) int {
 	var fpath = ls.CheckString(1)
-	ls.Push(lua.LString(wpk.Envfmt(fpath, nil)))
+	ls.Push(lua.LString(util.Envfmt(fpath, nil)))
 	return 1
 }
 
diff --git a/luawpk/luawpk.go b/luawpk/luawpk.go
index 94d4ac8..7ed474b 100644
--- a/luawpk/luawpk.go
+++ b/luawpk/luawpk.go
@@ -8,8 +8,9 @@ import (
 	"path"
 	"strings"
 
-	"github.com/schwarzlichtbezirk/wpk"
 	lua "github.com/yuin/gopher-lua"
+
+	"github.com/schwarzlichtbezirk/wpk"
 )
 
 // Package writer errors.
diff --git a/luawpk/nametid.go b/luawpk/nametid.go
index 55cf9fa..07a38b0 100644
--- a/luawpk/nametid.go
+++ b/luawpk/nametid.go
@@ -7,8 +7,9 @@ import (
 	"strconv"
 	"time"
 
-	"github.com/schwarzlichtbezirk/wpk"
 	lua "github.com/yuin/gopher-lua"
+
+	"github.com/schwarzlichtbezirk/wpk"
 )
 
 const (
diff --git a/luawpk/runlvm.go b/luawpk/runlvm.go
index 871baf6..12ab265 100644
--- a/luawpk/runlvm.go
+++ b/luawpk/runlvm.go
@@ -9,8 +9,9 @@ import (
 	"path"
 	"time"
 
-	"github.com/schwarzlichtbezirk/wpk"
 	lua "github.com/yuin/gopher-lua"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 var (
@@ -51,7 +52,7 @@ func luacheckfile(ls *lua.LState) int {
 
 func luabin2hex(ls *lua.LState) int {
 	var arg = ls.CheckString(1)
-	ls.Push(lua.LString(hex.EncodeToString(wpk.S2B(arg))))
+	ls.Push(lua.LString(hex.EncodeToString(util.S2B(arg))))
 	return 1
 }
 
@@ -67,7 +68,7 @@ func luahex2bin(ls *lua.LState) int {
 	if b, err = hex.DecodeString(arg); err != nil {
 		return 0
 	}
-	ls.Push(lua.LString(wpk.B2S(b)))
+	ls.Push(lua.LString(util.B2S(b)))
 	return 1
 }
 
@@ -106,9 +107,9 @@ func InitLuaVM(ls *lua.LState) {
 
 	var bindir = func() string {
 		if str, err := os.Executable(); err == nil {
-			return path.Dir(wpk.ToSlash(str))
+			return path.Dir(util.ToSlash(str))
 		} else {
-			return path.Dir(wpk.ToSlash(os.Args[0]))
+			return path.Dir(util.ToSlash(os.Args[0]))
 		}
 	}()
 
@@ -116,7 +117,7 @@ func InitLuaVM(ls *lua.LState) {
 	ls.SetGlobal("buildvers", lua.LString(BuildVers))
 	ls.SetGlobal("buildtime", lua.LString(BuildTime))
 	ls.SetGlobal("bindir", lua.LString(bindir))
-	ls.SetGlobal("tmpdir", lua.LString(wpk.ToSlash(os.TempDir())))
+	ls.SetGlobal("tmpdir", lua.LString(util.ToSlash(os.TempDir())))
 	// global functions
 	ls.SetGlobal("log", ls.NewFunction(lualog))
 	ls.SetGlobal("checkfile", ls.NewFunction(luacheckfile))
@@ -132,7 +133,7 @@ func RunLuaVM(fpath string) (err error) {
 	defer ls.Close()
 	InitLuaVM(ls)
 
-	var scrdir = path.Dir(wpk.ToSlash(fpath))
+	var scrdir = path.Dir(util.ToSlash(fpath))
 	ls.SetGlobal("scrdir", lua.LString(scrdir))
 
 	if err = ls.DoFile(fpath); err != nil {
diff --git a/tagset.go b/tagset.go
index d44a329..115386f 100644
--- a/tagset.go
+++ b/tagset.go
@@ -5,6 +5,8 @@ import (
 	"io/fs"
 	"path"
 	"time"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 var (
@@ -17,12 +19,12 @@ type TagRaw []byte
 
 // TagStr tag converter.
 func (t TagRaw) TagStr() (string, bool) {
-	return B2S(t), true
+	return util.B2S(t), true
 }
 
 // StrTag is string tag constructor.
 func StrTag(val string) TagRaw {
-	return S2B(val)
+	return util.S2B(val)
 }
 
 // TagBool is boolean tag converter.
@@ -59,7 +61,7 @@ func ByteTag(val byte) TagRaw {
 // TagUint16 is 16-bit unsigned int tag converter.
 func (t TagRaw) TagUint16() (uint16, bool) {
 	if len(t) == 2 {
-		return GetU16(t), true
+		return util.GetU16(t), true
 	}
 	return 0, false
 }
@@ -67,14 +69,14 @@ func (t TagRaw) TagUint16() (uint16, bool) {
 // Uint16Tag is 16-bit unsigned int tag constructor.
 func Uint16Tag(val uint16) TagRaw {
 	var buf [2]byte
-	SetU16(buf[:], val)
+	util.SetU16(buf[:], val)
 	return buf[:]
 }
 
 // TagUint32 is 32-bit unsigned int tag converter.
 func (t TagRaw) TagUint32() (uint32, bool) {
 	if len(t) == 4 {
-		return GetU32(t), true
+		return util.GetU32(t), true
 	}
 	return 0, false
 }
@@ -82,14 +84,14 @@ func (t TagRaw) TagUint32() (uint32, bool) {
 // Uint32Tag is 32-bit unsigned int tag constructor.
 func Uint32Tag(val uint32) TagRaw {
 	var buf [4]byte
-	SetU32(buf[:], val)
+	util.SetU32(buf[:], val)
 	return buf[:]
 }
 
 // TagUint64 is 64-bit unsigned int tag converter.
 func (t TagRaw) TagUint64() (uint64, bool) {
 	if len(t) == 8 {
-		return GetU64(t), true
+		return util.GetU64(t), true
 	}
 	return 0, false
 }
@@ -97,7 +99,7 @@ func (t TagRaw) TagUint64() (uint64, bool) {
 // Uint64Tag is 64-bit unsigned int tag constructor.
 func Uint64Tag(val uint64) TagRaw {
 	var buf [8]byte
-	SetU64(buf[:], val)
+	util.SetU64(buf[:], val)
 	return buf[:]
 }
 
@@ -105,11 +107,11 @@ func Uint64Tag(val uint64) TagRaw {
 func (t TagRaw) TagUint() (uint, bool) {
 	switch len(t) {
 	case 8:
-		return uint(GetU64(t)), true
+		return uint(util.GetU64(t)), true
 	case 4:
-		return uint(GetU32(t)), true
+		return uint(util.GetU32(t)), true
 	case 2:
-		return uint(GetU16(t)), true
+		return uint(util.GetU16(t)), true
 	case 1:
 		return uint(t[0]), true
 	}
@@ -121,15 +123,15 @@ func UintTag(val uint) TagRaw {
 	switch {
 	case val > 0xffffffff:
 		var buf [8]byte
-		SetU64(buf[:], uint64(val))
+		util.SetU64(buf[:], uint64(val))
 		return buf[:]
 	case val > 0xffff:
 		var buf [4]byte
-		SetU32(buf[:], uint32(val))
+		util.SetU32(buf[:], uint32(val))
 		return buf[:]
 	case val > 0xff:
 		var buf [2]byte
-		SetU16(buf[:], uint16(val))
+		util.SetU16(buf[:], uint16(val))
 		return buf[:]
 	default:
 		var buf [1]byte
@@ -143,15 +145,15 @@ func UintLenTag(val uint, l int) TagRaw {
 	switch l {
 	case 8:
 		var buf [8]byte
-		SetU64(buf[:], uint64(val))
+		util.SetU64(buf[:], uint64(val))
 		return buf[:]
 	case 4:
 		var buf [4]byte
-		SetU32(buf[:], uint32(val))
+		util.SetU32(buf[:], uint32(val))
 		return buf[:]
 	case 2:
 		var buf [2]byte
-		SetU16(buf[:], uint16(val))
+		util.SetU16(buf[:], uint16(val))
 		return buf[:]
 	case 1:
 		var buf [1]byte
@@ -165,7 +167,7 @@ func UintLenTag(val uint, l int) TagRaw {
 // TagNumber is 64-bit float tag converter.
 func (t TagRaw) TagNumber() (float64, bool) {
 	if len(t) == 8 {
-		return GetF64(t), true
+		return util.GetF64(t), true
 	}
 	return 0, false
 }
@@ -173,7 +175,7 @@ func (t TagRaw) TagNumber() (float64, bool) {
 // NumberTag is 64-bit float tag constructor.
 func NumberTag(val float64) TagRaw {
 	var buf [8]byte
-	SetF64(buf[:], val)
+	util.SetF64(buf[:], val)
 	return buf[:]
 }
 
@@ -181,11 +183,11 @@ func NumberTag(val float64) TagRaw {
 func (t TagRaw) TagTime() (time.Time, bool) {
 	switch len(t) {
 	case 8:
-		var milli = int64(GetU64(t))
+		var milli = int64(util.GetU64(t))
 		return time.Unix(milli/1000, (milli%1000)*1000000), true
 	case 12:
-		var sec = int64(GetU64(t[:8]))
-		var nsec = int64(GetU32(t[8:]))
+		var sec = int64(util.GetU64(t[:8]))
+		var nsec = int64(util.GetU32(t[8:]))
 		return time.Unix(sec, nsec), true
 	}
 	return time.Time{}, false
@@ -195,10 +197,10 @@ func (t TagRaw) TagTime() (time.Time, bool) {
 func (t TagRaw) TagUnixms() (int64, bool) {
 	switch len(t) {
 	case 8:
-		return int64(GetU64(t)), true
+		return int64(util.GetU64(t)), true
 	case 12:
-		var sec = int64(GetU64(t[:8]))
-		var nsec = int64(GetU32(t[8:]))
+		var sec = int64(util.GetU64(t[:8]))
+		var nsec = int64(util.GetU32(t[8:]))
 		return time.Unix(sec, nsec).UnixMilli(), true
 	}
 	return 0, false
@@ -207,15 +209,15 @@ func (t TagRaw) TagUnixms() (int64, bool) {
 // UnixmsTag is 8-bytes UNIX time in milliseconds tag constructor.
 func UnixmsTag(val time.Time) TagRaw {
 	var buf [8]byte
-	SetU64(buf[:], uint64(val.UnixMilli()))
+	util.SetU64(buf[:], uint64(val.UnixMilli()))
 	return buf[:]
 }
 
 // TimeTag is 12-bytes UNIX time tag constructor.
 func TimeTag(val time.Time) TagRaw {
 	var buf [12]byte
-	SetU64(buf[:8], uint64(val.Unix()))
-	SetU32(buf[8:], uint32(val.Nanosecond()))
+	util.SetU64(buf[:8], uint64(val.Unix()))
+	util.SetU32(buf[8:], uint32(val.Nanosecond()))
 	return buf[:]
 }
 
@@ -268,8 +270,8 @@ const taghdrsz = PTStidsz + PTStagsz
 // Can be used in chain calls at initialization.
 func (ts TagsetRaw) Put(tid TID, tag TagRaw) TagsetRaw {
 	var buf = make([]byte, taghdrsz+len(tag))
-	SetU16(buf, tid)
-	SetU16(buf[PTStidsz:], uint16(len(tag)))
+	util.SetU16(buf, tid)
+	util.SetU16(buf[PTStidsz:], uint16(len(tag)))
 	copy(buf[taghdrsz:], tag)
 	ts = append(ts, buf...)
 	return ts
@@ -315,7 +317,7 @@ func (ts TagsetRaw) SetOk(tid TID, tag TagRaw) (TagsetRaw, bool) {
 	if tl == uint16(tsi.pos-tsi.tag) {
 		copy(ts[tsi.tag:tsi.pos], tag)
 	} else {
-		SetU16(ts[tsi.tag-PTStagsz:tsi.tag], tl) // set tag length
+		util.SetU16(ts[tsi.tag-PTStagsz:tsi.tag], tl) // set tag length
 		var suff = ts[tsi.pos:]
 		ts = append(ts[:tsi.tag], tag...)
 		ts = append(ts, suff...)
@@ -602,13 +604,13 @@ func (tsi *TagsetIterator) Next() (ok bool) {
 	if tsi.pos += PTStidsz; tsi.pos > tsl {
 		return
 	}
-	var tid = GetU16(tsi.TagsetRaw[tsi.pos-PTStidsz : tsi.pos])
+	var tid = util.GetU16(tsi.TagsetRaw[tsi.pos-PTStidsz : tsi.pos])
 
 	// get tag length
 	if tsi.pos += PTStagsz; tsi.pos > tsl {
 		return
 	}
-	var len = GetU16(tsi.TagsetRaw[tsi.pos-PTStagsz : tsi.pos])
+	var len = util.GetU16(tsi.TagsetRaw[tsi.pos-PTStagsz : tsi.pos])
 	// store tag content position
 	var tag = tsi.pos
 
diff --git a/tagset_test.go b/tagset_test.go
index 7332928..3ff8bb9 100644
--- a/tagset_test.go
+++ b/tagset_test.go
@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/schwarzlichtbezirk/wpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 func TestTagset(t *testing.T) {
@@ -22,7 +23,7 @@ func TestTagset(t *testing.T) {
 	var ts = wpk.TagsetRaw{}.
 		Put(wpk.TIDoffset, wpk.UintTag(offset)).
 		Put(wpk.TIDsize, wpk.UintTag(size)).
-		Put(wpk.TIDpath, wpk.StrTag(wpk.ToSlash(fkey1))).
+		Put(wpk.TIDpath, wpk.StrTag(util.ToSlash(fkey1))).
 		Put(wpk.TIDfid, wpk.UintTag(fid))
 	var tsi = ts.Iterator()
 
@@ -41,8 +42,8 @@ func TestTagset(t *testing.T) {
 		}
 	}
 
-	assert(wpk.ToSlash(fkey1) == fkey, "toslash test failed")
-	assert(wpk.ToSlash(fkey2) == fkey, "toslash test failed")
+	assert(util.ToSlash(fkey1) == fkey, "toslash test failed")
+	assert(util.ToSlash(fkey2) == fkey, "toslash test failed")
 	assert(tsi.TID() == wpk.TIDnone, "tag ID in created iterator should be 'none'")
 	assert(ts.Num() == 4, "wrong number of tags")
 
@@ -108,7 +109,7 @@ func TestTagset(t *testing.T) {
 	ts, ok = ts.SetOk(wpk.TIDpath, wpk.StrTag(fkey))
 	assert(!ok, "content of 'path' tag should be replaced by 'Set'")
 	assert(ts.Num() == 4, "number of tags after replace 'path' must not be changed")
-	assert(ts.Path() == wpk.ToSlash(fkey2), "'Set' function does not work correctly")
+	assert(ts.Path() == util.ToSlash(fkey2), "'Set' function does not work correctly")
 	ts, ok = ts.SetOk(wpk.TIDmime, wpk.StrTag(mime))
 	assert(ok, "content of 'mime' tag should be added by 'Set'")
 	assert(ts.Num() == 4+1, "number of tags after add 'mime' must be added by one")
diff --git a/testdata/api.lua b/testdata/api.lua
index cd7e370..2dbae48 100644
--- a/testdata/api.lua
+++ b/testdata/api.lua
@@ -244,7 +244,7 @@ function wpk.create(fpath)-- additional wpk-constructor
 	pkg.autofid = true -- put auto generated file ID for each file
 	pkg.automime = true -- put MIME type for each file if it is not given explicit
 	pkg.crc32 = true -- generate CRC32 Castagnoli code for each file
-	pkg:begin(path.toslash(fpath)) -- open wpk-file for write
+	pkg:begin(fpath) -- open wpk-file for write
 	log("starts: "..pkg.pkgpath)
 	return pkg
 end
@@ -271,7 +271,7 @@ logfmt("script dir: %s", scrdir)
 logfmt("temporary dir: %s", tmpdir)
 
 -- starts new package at golang binary directory
-local pkg = wpk.create(path.envfmt"${GOPATH}/bin/api.wpk")
+local pkg = wpk.create(path.toslash(path.envfmt"${GOPATH}/bin/api.wpk"))
 pkg.label = "api-sample" -- image label
 pkg.secret = "package-private-key" -- private key to sign cryptographic hashes for each file
 pkg.sha224 = true -- generate SHA224 hash for each file
diff --git a/union.go b/union.go
index 24a5b50..9984f15 100644
--- a/union.go
+++ b/union.go
@@ -6,6 +6,8 @@ import (
 	"path"
 	"strconv"
 	"strings"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // Void is empty structure to release of the set of keys.
@@ -109,7 +111,7 @@ func (u *Union) Stat(fpath string) (fs.FileInfo, error) {
 // Glob returns the names of all files in union matching pattern or nil
 // if there is no matching file.
 func (u *Union) Glob(pattern string) (res []string, err error) {
-	pattern = ToSlash(pattern)
+	pattern = util.ToSlash(pattern)
 	if _, err = path.Match(pattern, ""); err != nil {
 		return
 	}
@@ -152,7 +154,7 @@ func (u *Union) ReadFile(fpath string) ([]byte, error) {
 // ReadDir reads the named directory
 // and returns a list of directory entries sorted by filename.
 func (u *Union) ReadDirN(dir string, n int) (list []fs.DirEntry, err error) {
-	dir = ToSlash(dir)
+	dir = util.ToSlash(dir)
 	var found = map[string]fs.DirEntry{}
 	var ni = n
 	for _, pkg := range u.List {
@@ -170,7 +172,7 @@ func (u *Union) ReadDirN(dir string, n int) (list []fs.DirEntry, err error) {
 					found[suffix] = ts
 					ni--
 				} else { // dir detected
-					var subdir = JoinPath(prefix, suffix[:sp])
+					var subdir = util.JoinPath(prefix, suffix[:sp])
 					if _, ok := found[subdir]; !ok {
 						var dts = TagsetRaw{}.
 							Put(TIDpath, StrTag(subdir))
@@ -214,7 +216,7 @@ func (u *Union) ReadDir(dir string) ([]fs.DirEntry, error) {
 // If union have more than one file with the same name, first will be returned.
 // fs.FS implementation.
 func (u *Union) Open(dir string) (fs.File, error) {
-	dir = ToSlash(dir)
+	dir = util.ToSlash(dir)
 	if len(u.List) == 0 {
 		return nil, &fs.PathError{Op: "open", Path: dir, Err: fs.ErrNotExist}
 	}
diff --git a/union_test.go b/union_test.go
index 87b7955..5028414 100644
--- a/union_test.go
+++ b/union_test.go
@@ -9,6 +9,7 @@ import (
 	"github.com/schwarzlichtbezirk/wpk"
 	"github.com/schwarzlichtbezirk/wpk/bulk"
 	"github.com/schwarzlichtbezirk/wpk/mmap"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 var testpack1 = wpk.TempPath("testpack1.wpk")
@@ -123,7 +124,7 @@ func TestUnion(t *testing.T) {
 				var delist, _ = df.ReadDir(-1)
 				list = make([]string, len(delist))
 				for i, de := range delist {
-					list[i] = wpk.JoinPath(fpath, de.Name())
+					list[i] = util.JoinPath(fpath, de.Name())
 				}
 			} else {
 				t.Fatalf("cannot cast '%s' directory property to fs.ReadDirFile", fpath)
@@ -218,7 +219,7 @@ func TestUnion(t *testing.T) {
 	// ReadFile test
 	//
 
-	var imgfpath = wpk.JoinPath(mediadir, "img1/Qarataşlar.jpg")
+	var imgfpath = util.JoinPath(mediadir, "img1/Qarataşlar.jpg")
 	var imgb, pkgb []byte
 	if imgb, err = os.ReadFile(imgfpath); err != nil {
 		t.Fatal(err)
diff --git a/seqmap.go b/util/seqmap.go
similarity index 99%
rename from seqmap.go
rename to util/seqmap.go
index ff4ba43..4479db5 100644
--- a/seqmap.go
+++ b/util/seqmap.go
@@ -1,4 +1,4 @@
-package wpk
+package util
 
 import (
 	"sync"
diff --git a/strutil.go b/util/strutil.go
similarity index 99%
rename from strutil.go
rename to util/strutil.go
index f972881..8f3985e 100644
--- a/strutil.go
+++ b/util/strutil.go
@@ -1,4 +1,4 @@
-package wpk
+package util
 
 import (
 	"os"
diff --git a/strutil_test.go b/util/strutil_test.go
similarity index 53%
rename from strutil_test.go
rename to util/strutil_test.go
index e09f193..39c5efe 100644
--- a/strutil_test.go
+++ b/util/strutil_test.go
@@ -1,4 +1,4 @@
-package wpk_test
+package util_test
 
 import (
 	"fmt"
@@ -6,7 +6,7 @@ import (
 	"testing"
 	"unsafe"
 
-	"github.com/schwarzlichtbezirk/wpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 func TestS2B(t *testing.T) {
@@ -17,7 +17,7 @@ func TestS2B(t *testing.T) {
 	if ps == pb {
 		t.Error("string pointer is equal to pointer on new allocated bytes slice")
 	}*/
-	var b = wpk.S2B(s)
+	var b = util.S2B(s)
 	var pb = unsafe.Pointer(unsafe.SliceData(b))
 	if ps != pb {
 		t.Error("string pointer is not equal to pointer on same bytes slice")
@@ -32,7 +32,7 @@ func TestB2S(t *testing.T) {
 	if pb == ps {
 		t.Error("bytes slice pointer is equal to pointer on new allocated string")
 	}
-	s = wpk.B2S(b)
+	s = util.B2S(b)
 	ps = unsafe.Pointer(unsafe.StringData(s))
 	if pb != ps {
 		t.Error("bytes slice pointer is not equal to pointer on same string")
@@ -40,30 +40,30 @@ func TestB2S(t *testing.T) {
 }
 
 func ExampleToSlash() {
-	fmt.Println(wpk.ToSlash("C:\\Windows\\Temp"))
+	fmt.Println(util.ToSlash("C:\\Windows\\Temp"))
 	// Output: C:/Windows/Temp
 }
 
 func ExampleToLower() {
-	fmt.Println(wpk.ToLower("C:\\Windows\\Temp"))
+	fmt.Println(util.ToLower("C:\\Windows\\Temp"))
 	// Output: c:\windows\temp
 }
 
 func ExampleToUpper() {
-	fmt.Println(wpk.ToUpper("C:\\Windows\\Temp"))
+	fmt.Println(util.ToUpper("C:\\Windows\\Temp"))
 	// Output: C:\WINDOWS\TEMP
 }
 
 func ExampleToKey() {
-	fmt.Println(wpk.ToKey("C:\\Windows\\Temp"))
+	fmt.Println(util.ToKey("C:\\Windows\\Temp"))
 	// Output: c:/windows/temp
 }
 
 func ExampleJoinPath() {
-	fmt.Println(wpk.JoinPath("dir", "base.ext"))
-	fmt.Println(wpk.JoinPath("dir/", "base.ext"))
-	fmt.Println(wpk.JoinPath("dir", "/base.ext"))
-	fmt.Println(wpk.JoinPath("dir/", "/base.ext"))
+	fmt.Println(util.JoinPath("dir", "base.ext"))
+	fmt.Println(util.JoinPath("dir/", "base.ext"))
+	fmt.Println(util.JoinPath("dir", "/base.ext"))
+	fmt.Println(util.JoinPath("dir/", "/base.ext"))
 	// Output:
 	// dir/base.ext
 	// dir/base.ext
@@ -72,9 +72,9 @@ func ExampleJoinPath() {
 }
 
 func ExampleJoinFilePath() {
-	fmt.Println(wpk.JoinFilePath("dir/", "base.ext"))
-	fmt.Println(wpk.JoinFilePath("dir", "/base.ext"))
-	fmt.Println(wpk.JoinFilePath("dir/", "/base.ext"))
+	fmt.Println(util.JoinFilePath("dir/", "base.ext"))
+	fmt.Println(util.JoinFilePath("dir", "/base.ext"))
+	fmt.Println(util.JoinFilePath("dir/", "/base.ext"))
 	// Output:
 	// dir/base.ext
 	// dir/base.ext
@@ -82,12 +82,12 @@ func ExampleJoinFilePath() {
 }
 
 func ExamplePathName() {
-	fmt.Println(wpk.PathName("C:\\Windows\\system.ini"))
-	fmt.Println(wpk.PathName("/go/bin/wpkbuild_win_x64.exe"))
-	fmt.Println(wpk.PathName("wpkbuild_win_x64.exe"))
-	fmt.Println(wpk.PathName("/go/bin/wpkbuild_linux_x64"))
-	fmt.Println(wpk.PathName("wpkbuild_linux_x64"))
-	fmt.Printf("'%s'\n", wpk.PathName("/go/bin/"))
+	fmt.Println(util.PathName("C:\\Windows\\system.ini"))
+	fmt.Println(util.PathName("/go/bin/wpkbuild_win_x64.exe"))
+	fmt.Println(util.PathName("wpkbuild_win_x64.exe"))
+	fmt.Println(util.PathName("/go/bin/wpkbuild_linux_x64"))
+	fmt.Println(util.PathName("wpkbuild_linux_x64"))
+	fmt.Printf("'%s'\n", util.PathName("/go/bin/"))
 	// Output:
 	// system
 	// wpkbuild_win_x64
@@ -100,20 +100,20 @@ func ExamplePathName() {
 func ExampleEnvfmt() {
 	os.Setenv("VAR", "/go")
 	// successful patterns
-	fmt.Println(wpk.Envfmt("$VAR/bin/", nil))
-	fmt.Println(wpk.Envfmt("${VAR}/bin/", nil))
-	fmt.Println(wpk.Envfmt("%VAR%/bin/", nil))
-	fmt.Println(wpk.Envfmt("/home$VAR", nil))
-	fmt.Println(wpk.Envfmt("/home%VAR%", map[string]string{"VAR": "/any/path"}))
-	fmt.Println(wpk.Envfmt("$VAR%VAR%${VAR}", nil))
+	fmt.Println(util.Envfmt("$VAR/bin/", nil))
+	fmt.Println(util.Envfmt("${VAR}/bin/", nil))
+	fmt.Println(util.Envfmt("%VAR%/bin/", nil))
+	fmt.Println(util.Envfmt("/home$VAR", nil))
+	fmt.Println(util.Envfmt("/home%VAR%", map[string]string{"VAR": "/any/path"}))
+	fmt.Println(util.Envfmt("$VAR%VAR%${VAR}", nil))
 	// patterns with unknown variable
-	fmt.Println(wpk.Envfmt("$VYR/bin/", nil))
-	fmt.Println(wpk.Envfmt("${VAR}/${_foo_}", nil))
+	fmt.Println(util.Envfmt("$VYR/bin/", nil))
+	fmt.Println(util.Envfmt("${VAR}/${_foo_}", nil))
 	// patterns with errors
-	fmt.Println(wpk.Envfmt("$VAR$/bin/", nil))
-	fmt.Println(wpk.Envfmt("${VAR/bin/", nil))
-	fmt.Println(wpk.Envfmt("%VAR/bin/", nil))
-	fmt.Println(wpk.Envfmt("/home${VAR", nil))
+	fmt.Println(util.Envfmt("$VAR$/bin/", nil))
+	fmt.Println(util.Envfmt("${VAR/bin/", nil))
+	fmt.Println(util.Envfmt("%VAR/bin/", nil))
+	fmt.Println(util.Envfmt("/home${VAR", nil))
 	// Output:
 	// /go/bin/
 	// /go/bin/
diff --git a/uintio.go b/util/uintio.go
similarity index 99%
rename from uintio.go
rename to util/uintio.go
index 1aa6292..31112b3 100644
--- a/uintio.go
+++ b/util/uintio.go
@@ -1,4 +1,4 @@
-package wpk
+package util
 
 import (
 	"io"
diff --git a/wpk.go b/wpk.go
index 0f94b3c..a5cb640 100644
--- a/wpk.go
+++ b/wpk.go
@@ -9,6 +9,8 @@ import (
 	"path"
 	"strings"
 	"sync"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 const (
@@ -157,14 +159,14 @@ func (hdr *Header) DataSize() uint {
 // IsReady determines that package is ready for read the data.
 func (hdr *Header) IsReady() error {
 	// can not read file tags table for opened on write single-file package.
-	if B2S(hdr.signature[:]) == SignBuild {
+	if util.B2S(hdr.signature[:]) == SignBuild {
 		if hdr.datoffset != 0 {
 			return ErrSignPre
 		}
 		return nil
 	}
 	// can not read file tags table on any incorrect signature
-	if B2S(hdr.signature[:]) != SignReady {
+	if util.B2S(hdr.signature[:]) != SignReady {
 		return ErrSignBad
 	}
 	return nil
@@ -179,15 +181,15 @@ func (hdr *Header) Parse(buf []byte) (n int64, err error) {
 	}
 	copy(hdr.signature[:], buf)
 	n += SignSize
-	hdr.fttcount = GetU64(buf[n:])
+	hdr.fttcount = util.GetU64(buf[n:])
 	n += 8
-	hdr.fttoffset = GetU64(buf[n:])
+	hdr.fttoffset = util.GetU64(buf[n:])
 	n += 8
-	hdr.fttsize = GetU64(buf[n:])
+	hdr.fttsize = util.GetU64(buf[n:])
 	n += 8
-	hdr.datoffset = GetU64(buf[n:])
+	hdr.datoffset = util.GetU64(buf[n:])
 	n += 8
-	hdr.datsize = GetU64(buf[n:])
+	hdr.datsize = util.GetU64(buf[n:])
 	n += 8
 	return
 }
@@ -198,23 +200,23 @@ func (hdr *Header) ReadFrom(r io.Reader) (n int64, err error) {
 		return
 	}
 	n += SignSize
-	if hdr.fttcount, err = ReadU64(r); err != nil {
+	if hdr.fttcount, err = util.ReadU64(r); err != nil {
 		return
 	}
 	n += 8
-	if hdr.fttoffset, err = ReadU64(r); err != nil {
+	if hdr.fttoffset, err = util.ReadU64(r); err != nil {
 		return
 	}
 	n += 8
-	if hdr.fttsize, err = ReadU64(r); err != nil {
+	if hdr.fttsize, err = util.ReadU64(r); err != nil {
 		return
 	}
 	n += 8
-	if hdr.datoffset, err = ReadU64(r); err != nil {
+	if hdr.datoffset, err = util.ReadU64(r); err != nil {
 		return
 	}
 	n += 8
-	if hdr.datsize, err = ReadU64(r); err != nil {
+	if hdr.datsize, err = util.ReadU64(r); err != nil {
 		return
 	}
 	n += 8
@@ -227,23 +229,23 @@ func (hdr *Header) WriteTo(w io.Writer) (n int64, err error) {
 		return
 	}
 	n += SignSize
-	if err = WriteU64(w, hdr.fttcount); err != nil {
+	if err = util.WriteU64(w, hdr.fttcount); err != nil {
 		return
 	}
 	n += 8
-	if err = WriteU64(w, hdr.fttoffset); err != nil {
+	if err = util.WriteU64(w, hdr.fttoffset); err != nil {
 		return
 	}
 	n += 8
-	if err = WriteU64(w, hdr.fttsize); err != nil {
+	if err = util.WriteU64(w, hdr.fttsize); err != nil {
 		return
 	}
 	n += 8
-	if err = WriteU64(w, hdr.datoffset); err != nil {
+	if err = util.WriteU64(w, hdr.datoffset); err != nil {
 		return
 	}
 	n += 8
-	if err = WriteU64(w, hdr.datsize); err != nil {
+	if err = util.WriteU64(w, hdr.datsize); err != nil {
 		return
 	}
 	n += 8
@@ -255,8 +257,8 @@ const PackName = "@pack"
 
 // File tags table.
 type FTT struct {
-	info TagsetRaw                 // special tagset with package tags
-	tsm  SeqMap[string, TagsetRaw] // keys - package filenames (case sensitive), values - tagset slices.
+	info TagsetRaw                      // special tagset with package tags
+	tsm  util.SeqMap[string, TagsetRaw] // keys - package filenames (case sensitive), values - tagset slices.
 
 	datoffset uint64 // files data offset
 	datsize   uint64 // files data total size
@@ -358,7 +360,7 @@ func (ftt *FTT) CheckTagset(ts TagsetRaw) (fkey string, err error) {
 // It's high performance method without extra allocations calls.
 func (ftt *FTT) Parse(buf []byte) (n int64, err error) {
 	{
-		var tsl = GetU16(buf[n : n+PTStssize])
+		var tsl = util.GetU16(buf[n : n+PTStssize])
 		n += PTStssize
 
 		var ts = TagsetRaw(buf[n : n+int64(tsl)])
@@ -376,7 +378,7 @@ func (ftt *FTT) Parse(buf []byte) (n int64, err error) {
 	}
 
 	for {
-		var tsl = GetU16(buf[n : n+PTStssize])
+		var tsl = util.GetU16(buf[n : n+PTStssize])
 		n += PTStssize
 
 		if tsl == 0 {
@@ -391,7 +393,7 @@ func (ftt *FTT) Parse(buf []byte) (n int64, err error) {
 			return
 		}
 
-		ftt.tsm.Poke(ToSlash(fkey), ts)
+		ftt.tsm.Poke(util.ToSlash(fkey), ts)
 	}
 	return
 }
@@ -401,7 +403,7 @@ func (ftt *FTT) ReadFrom(r io.Reader) (n int64, err error) {
 	// read tagset with package info at first, can be empty
 	{
 		var tsl uint16
-		if tsl, err = ReadU16(r); err != nil {
+		if tsl, err = util.ReadU16(r); err != nil {
 			return
 		}
 		n += PTStssize
@@ -425,7 +427,7 @@ func (ftt *FTT) ReadFrom(r io.Reader) (n int64, err error) {
 
 	for {
 		var tsl uint16
-		if tsl, err = ReadU16(r); err != nil {
+		if tsl, err = util.ReadU16(r); err != nil {
 			return
 		}
 		n += PTStssize
@@ -445,7 +447,7 @@ func (ftt *FTT) ReadFrom(r io.Reader) (n int64, err error) {
 			return
 		}
 
-		ftt.tsm.Poke(ToSlash(fkey), ts)
+		ftt.tsm.Poke(util.ToSlash(fkey), ts)
 	}
 	return
 }
@@ -461,7 +463,7 @@ func (ftt *FTT) WriteTo(w io.Writer) (n int64, err error) {
 		}
 
 		// write tagset length
-		if err = WriteU16(w, uint16(tsl)); err != nil {
+		if err = util.WriteU16(w, uint16(tsl)); err != nil {
 			return
 		}
 		n += PTStssize
@@ -482,7 +484,7 @@ func (ftt *FTT) WriteTo(w io.Writer) (n int64, err error) {
 		}
 
 		// write tagset length
-		if err = WriteU16(w, uint16(tsl)); err != nil {
+		if err = util.WriteU16(w, uint16(tsl)); err != nil {
 			return false
 		}
 		n += PTStssize
@@ -498,7 +500,7 @@ func (ftt *FTT) WriteTo(w io.Writer) (n int64, err error) {
 		return
 	}
 	// write tags table end marker
-	if err = WriteU16(w, 0); err != nil {
+	if err = util.WriteU16(w, 0); err != nil {
 		return
 	}
 	n += PTStssize
@@ -583,7 +585,7 @@ func NewPackage() *Package {
 
 // FullPath returns concatenation of workspace and relative path.
 func (pkg *Package) FullPath(fkey string) string {
-	return JoinPath(pkg.Workspace, fkey)
+	return util.JoinPath(pkg.Workspace, fkey)
 }
 
 // TrimPath returns trimmed path without workspace prefix.
@@ -610,22 +612,22 @@ func (pkg *Package) BaseTagset(offset, size uint, fkey string) TagsetRaw {
 	return TagsetRaw{}.
 		Put(TIDoffset, UintTag(offset)).
 		Put(TIDsize, UintTag(size)).
-		Put(TIDpath, StrTag(pkg.FullPath(ToSlash(fkey))))
+		Put(TIDpath, StrTag(pkg.FullPath(util.ToSlash(fkey))))
 }
 
 // HasTagset check up that tagset with given filename key is present.
 func (pkg *Package) HasTagset(fkey string) bool {
-	return pkg.tsm.Has(pkg.FullPath(ToSlash(fkey)))
+	return pkg.tsm.Has(pkg.FullPath(util.ToSlash(fkey)))
 }
 
 // GetTagset returns tagset with given filename key, if it found.
 func (pkg *Package) GetTagset(fkey string) (TagsetRaw, bool) {
-	return pkg.tsm.Peek(pkg.FullPath(ToSlash(fkey)))
+	return pkg.tsm.Peek(pkg.FullPath(util.ToSlash(fkey)))
 }
 
 // SetTagset puts tagset with given filename key.
 func (pkg *Package) SetTagset(fkey string, ts TagsetRaw) {
-	pkg.tsm.Poke(pkg.FullPath(ToSlash(fkey)), ts)
+	pkg.tsm.Poke(pkg.FullPath(util.ToSlash(fkey)), ts)
 }
 
 // SetupTagset puts tagset with filename key stored at tagset.
@@ -635,7 +637,7 @@ func (pkg *Package) SetupTagset(ts TagsetRaw) {
 
 // GetDelTagset deletes the tagset for a key, returning the previous tagset if any.
 func (pkg *Package) DelTagset(fkey string) (TagsetRaw, bool) {
-	return pkg.tsm.Delete(pkg.FullPath(ToSlash(fkey)))
+	return pkg.tsm.Delete(pkg.FullPath(util.ToSlash(fkey)))
 }
 
 // Enum calls given closure for each tagset in package. Skips package info.
@@ -654,14 +656,14 @@ func (pkg *Package) Enum(f func(string, TagsetRaw) bool) {
 func (pkg *Package) Sub(dir string) (sub fs.FS, err error) {
 	var prefix string
 	if dir != "." && dir != "" {
-		prefix = ToSlash(dir) + "/" // make prefix slash-terminated
+		prefix = util.ToSlash(dir) + "/" // make prefix slash-terminated
 	}
 	pkg.Enum(func(fkey string, ts TagsetRaw) bool {
 		if strings.HasPrefix(fkey, prefix) {
 			sub = &Package{
 				FTT:       pkg.FTT,
 				Tagger:    pkg.Tagger,
-				Workspace: pkg.FullPath(ToSlash(dir)),
+				Workspace: pkg.FullPath(util.ToSlash(dir)),
 			}
 			return false
 		}
@@ -686,7 +688,7 @@ func (pkg *Package) Stat(fkey string) (fs.FileInfo, error) {
 // if there is no matching file.
 // fs.GlobFS interface implementation.
 func (pkg *Package) Glob(pattern string) (res []string, err error) {
-	pattern = ToSlash(pattern)
+	pattern = util.ToSlash(pattern)
 	if _, err = path.Match(pattern, ""); err != nil {
 		return
 	}
@@ -763,7 +765,7 @@ func GetPackageInfo(r io.ReadSeeker) (hdr Header, ts TagsetRaw, err error) {
 
 	// read first tagset that should be package info
 	var tsl uint16
-	if tsl, err = ReadU16(r); err != nil {
+	if tsl, err = util.ReadU16(r); err != nil {
 		return
 	}
 
diff --git a/wpk_test.go b/wpk_test.go
index 6db702b..7bf2bc2 100644
--- a/wpk_test.go
+++ b/wpk_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 
 	"github.com/schwarzlichtbezirk/wpk"
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 const mediadir = "testdata/media/"
@@ -16,7 +17,7 @@ var testpkgt = wpk.TempPath("testpack.wpt")
 var testpkgf = wpk.TempPath("testpack.wpf")
 
 var memdata = map[string][]byte{
-	"sample.txt": wpk.S2B("The quick brown fox jumps over the lazy dog"),
+	"sample.txt": util.S2B("The quick brown fox jumps over the lazy dog"),
 	"array.dat": {
 		0, 1, 2, 3, 4, 5, 6, 7, 8, 9,
 		100, 101, 102, 103, 104, 105, 106, 107, 108, 109,
@@ -182,7 +183,7 @@ func TestPackDir(t *testing.T) {
 			return nil // file is directory
 		}
 
-		var fpath = wpk.JoinPath(mediadir, fkey)
+		var fpath = util.JoinPath(mediadir, fkey)
 		var file fs.File
 		var ts wpk.TagsetRaw
 		if file, err = os.Open(fpath); err != nil {
@@ -304,7 +305,7 @@ func TestPackDirSplit(t *testing.T) {
 			return nil // file is directory
 		}
 
-		var fpath = wpk.JoinPath(mediadir, fkey)
+		var fpath = util.JoinPath(mediadir, fkey)
 		var file fs.File
 		var ts wpk.TagsetRaw
 		if file, err = os.Open(fpath); err != nil {
diff --git a/writer.go b/writer.go
index 8a87cf2..25a043f 100644
--- a/writer.go
+++ b/writer.go
@@ -7,6 +7,8 @@ import (
 	"strings"
 
 	"gopkg.in/djherbis/times.v1"
+
+	"github.com/schwarzlichtbezirk/wpk/util"
 )
 
 // WriteSeekCloser is typical useful interface for package writing.
@@ -27,7 +29,7 @@ func (ftt *FTT) Begin(wpt, wpf io.WriteSeeker) (err error) {
 		offset = HeaderSize
 	}
 	var hdr = Header{
-		signature: [SignSize]byte(S2B(SignBuild)),
+		signature: [SignSize]byte(util.S2B(SignBuild)),
 		fttcount:  0,
 		fttoffset: offset,
 		fttsize:   0,
@@ -55,7 +57,7 @@ func (ftt *FTT) Append(wpt, wpf io.WriteSeeker) (err error) {
 		return
 	}
 	// rewrite prebuild signature
-	if _, err = wpt.Write(S2B(SignBuild)); err != nil {
+	if _, err = wpt.Write(util.S2B(SignBuild)); err != nil {
 		return
 	}
 	// go to tags table start to replace it by new data
@@ -117,7 +119,7 @@ func (ftt *FTT) Sync(wpt, wpf io.WriteSeeker) (err error) {
 
 	// rewrite true header
 	var hdr = Header{
-		signature: [SignSize]byte(S2B(SignReady)),
+		signature: [SignSize]byte(util.S2B(SignReady)),
 		fttcount:  uint64(ftt.tsm.Len()),
 		fttoffset: uint64(fftpos),
 		fttsize:   uint64(fftend - fftpos),
@@ -202,7 +204,7 @@ func (pkg *Package) Rename(fkey1, fkey2 string) error {
 		return &fs.PathError{Op: "rename", Path: fkey2, Err: fs.ErrExist}
 	}
 
-	ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(ToSlash(fkey2))))
+	ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(util.ToSlash(fkey2))))
 	pkg.DelTagset(fkey1)
 	pkg.SetTagset(fkey2, ts)
 	return nil
@@ -223,7 +225,7 @@ func (pkg *Package) RenameDir(olddir, newdir string, skipexist bool) (count int,
 				err = &fs.PathError{Op: "renamedir", Path: newkey, Err: fs.ErrExist}
 				return skipexist
 			}
-			ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(ToSlash(newkey))))
+			ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(util.ToSlash(newkey))))
 			pkg.DelTagset(fkey)
 			pkg.SetTagset(newkey, ts)
 			count++
@@ -247,7 +249,7 @@ func (pkg *Package) PutAlias(fkey1, fkey2 string) error {
 		return &fs.PathError{Op: "putalias", Path: fkey2, Err: fs.ErrExist}
 	}
 
-	ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(ToSlash(fkey2))))
+	ts = CopyTagset(ts).Set(TIDpath, StrTag(pkg.FullPath(util.ToSlash(fkey2))))
 	pkg.SetTagset(fkey2, ts)
 	return nil
 }