diff --git a/src/archive/tar/common.go b/src/archive/tar/common.go
index 2a1e432182..38997fe754 100644
--- a/src/archive/tar/common.go
+++ b/src/archive/tar/common.go
@@ -13,7 +13,6 @@
 package tar
 
 import (
-	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -271,28 +270,6 @@ func FileInfoHeader(fi os.FileInfo, link string) (*Header, error) {
 	return h, nil
 }
 
-func isASCII(s string) bool {
-	for _, c := range s {
-		if c >= 0x80 {
-			return false
-		}
-	}
-	return true
-}
-
-func toASCII(s string) string {
-	if isASCII(s) {
-		return s
-	}
-	var buf bytes.Buffer
-	for _, c := range s {
-		if c < 0x80 {
-			buf.WriteByte(byte(c))
-		}
-	}
-	return buf.String()
-}
-
 // isHeaderOnlyType checks if the given type flag is of the type that has no
 // data section even if a size is specified.
 func isHeaderOnlyType(flag byte) bool {
diff --git a/src/archive/tar/reader.go b/src/archive/tar/reader.go
index fa1c48adeb..462fb8d5d4 100644
--- a/src/archive/tar/reader.go
+++ b/src/archive/tar/reader.go
@@ -22,8 +22,6 @@ var (
 	ErrHeader = errors.New("archive/tar: invalid tar header")
 )
 
-const maxNanoSecondIntSize = 9
-
 // A Reader provides sequential access to the contents of a tar archive.
 // A tar archive consists of a sequence of files.
 // The Next method advances to the next file in the archive (including the first),
@@ -40,10 +38,6 @@ type Reader struct {
 	err error
 }
 
-type parser struct {
-	err error // Last error seen
-}
-
 // A numBytesReader is an io.Reader with a numBytes method, returning the number
 // of bytes remaining in the underlying encoded data.
 type numBytesReader interface {
@@ -346,42 +340,6 @@ func mergePAX(hdr *Header, headers map[string]string) (err error) {
 	return nil
 }
 
-// parsePAXTime takes a string of the form %d.%d as described in
-// the PAX specification.
-func parsePAXTime(t string) (time.Time, error) {
-	buf := []byte(t)
-	pos := bytes.IndexByte(buf, '.')
-	var seconds, nanoseconds int64
-	var err error
-	if pos == -1 {
-		seconds, err = strconv.ParseInt(t, 10, 0)
-		if err != nil {
-			return time.Time{}, err
-		}
-	} else {
-		seconds, err = strconv.ParseInt(string(buf[:pos]), 10, 0)
-		if err != nil {
-			return time.Time{}, err
-		}
-		nanoBuf := string(buf[pos+1:])
-		// Pad as needed before converting to a decimal.
-		// For example .030 -> .030000000 -> 30000000 nanoseconds
-		if len(nanoBuf) < maxNanoSecondIntSize {
-			// Right pad
-			nanoBuf += strings.Repeat("0", maxNanoSecondIntSize-len(nanoBuf))
-		} else if len(nanoBuf) > maxNanoSecondIntSize {
-			// Right truncate
-			nanoBuf = nanoBuf[:maxNanoSecondIntSize]
-		}
-		nanoseconds, err = strconv.ParseInt(nanoBuf, 10, 0)
-		if err != nil {
-			return time.Time{}, err
-		}
-	}
-	ts := time.Unix(seconds, nanoseconds)
-	return ts, nil
-}
-
 // parsePAX parses PAX headers.
 // If an extended header (type 'x') is invalid, ErrHeader is returned
 func parsePAX(r io.Reader) (map[string]string, error) {
@@ -423,111 +381,6 @@ func parsePAX(r io.Reader) (map[string]string, error) {
 	return headers, nil
 }
 
-// parsePAXRecord parses the input PAX record string into a key-value pair.
-// If parsing is successful, it will slice off the currently read record and
-// return the remainder as r.
-//
-// A PAX record is of the following form:
-//	"%d %s=%s\n" % (size, key, value)
-func parsePAXRecord(s string) (k, v, r string, err error) {
-	// The size field ends at the first space.
-	sp := strings.IndexByte(s, ' ')
-	if sp == -1 {
-		return "", "", s, ErrHeader
-	}
-
-	// Parse the first token as a decimal integer.
-	n, perr := strconv.ParseInt(s[:sp], 10, 0) // Intentionally parse as native int
-	if perr != nil || n < 5 || int64(len(s)) < n {
-		return "", "", s, ErrHeader
-	}
-
-	// Extract everything between the space and the final newline.
-	rec, nl, rem := s[sp+1:n-1], s[n-1:n], s[n:]
-	if nl != "\n" {
-		return "", "", s, ErrHeader
-	}
-
-	// The first equals separates the key from the value.
-	eq := strings.IndexByte(rec, '=')
-	if eq == -1 {
-		return "", "", s, ErrHeader
-	}
-	return rec[:eq], rec[eq+1:], rem, nil
-}
-
-// parseString parses bytes as a NUL-terminated C-style string.
-// If a NUL byte is not found then the whole slice is returned as a string.
-func (*parser) parseString(b []byte) string {
-	n := 0
-	for n < len(b) && b[n] != 0 {
-		n++
-	}
-	return string(b[0:n])
-}
-
-// parseNumeric parses the input as being encoded in either base-256 or octal.
-// This function may return negative numbers.
-// If parsing fails or an integer overflow occurs, err will be set.
-func (p *parser) parseNumeric(b []byte) int64 {
-	// Check for base-256 (binary) format first.
-	// If the first bit is set, then all following bits constitute a two's
-	// complement encoded number in big-endian byte order.
-	if len(b) > 0 && b[0]&0x80 != 0 {
-		// Handling negative numbers relies on the following identity:
-		//	-a-1 == ^a
-		//
-		// If the number is negative, we use an inversion mask to invert the
-		// data bytes and treat the value as an unsigned number.
-		var inv byte // 0x00 if positive or zero, 0xff if negative
-		if b[0]&0x40 != 0 {
-			inv = 0xff
-		}
-
-		var x uint64
-		for i, c := range b {
-			c ^= inv // Inverts c only if inv is 0xff, otherwise does nothing
-			if i == 0 {
-				c &= 0x7f // Ignore signal bit in first byte
-			}
-			if (x >> 56) > 0 {
-				p.err = ErrHeader // Integer overflow
-				return 0
-			}
-			x = x<<8 | uint64(c)
-		}
-		if (x >> 63) > 0 {
-			p.err = ErrHeader // Integer overflow
-			return 0
-		}
-		if inv == 0xff {
-			return ^int64(x)
-		}
-		return int64(x)
-	}
-
-	// Normal case is base-8 (octal) format.
-	return p.parseOctal(b)
-}
-
-func (p *parser) parseOctal(b []byte) int64 {
-	// Because unused fields are filled with NULs, we need
-	// to skip leading NULs. Fields may also be padded with
-	// spaces or NULs.
-	// So we remove leading and trailing NULs and spaces to
-	// be sure.
-	b = bytes.Trim(b, " \x00")
-
-	if len(b) == 0 {
-		return 0
-	}
-	x, perr := strconv.ParseUint(p.parseString(b), 8, 64)
-	if perr != nil {
-		p.err = ErrHeader
-	}
-	return int64(x)
-}
-
 // skipUnread skips any unread bytes in the existing file entry, as well as any
 // alignment padding. It returns io.ErrUnexpectedEOF if any io.EOF is
 // encountered in the data portion; it is okay to hit io.EOF in the padding.
diff --git a/src/archive/tar/reader_test.go b/src/archive/tar/reader_test.go
index 9ffc8d6459..15b942fafe 100644
--- a/src/archive/tar/reader_test.go
+++ b/src/archive/tar/reader_test.go
@@ -465,81 +465,6 @@ func TestPartialRead(t *testing.T) {
 	}
 }
 
-func TestParsePAXHeader(t *testing.T) {
-	paxTests := [][3]string{
-		{"a", "a=name", "10 a=name\n"}, // Test case involving multiple acceptable lengths
-		{"a", "a=name", "9 a=name\n"},  // Test case involving multiple acceptable length
-		{"mtime", "mtime=1350244992.023960108", "30 mtime=1350244992.023960108\n"}}
-	for _, test := range paxTests {
-		key, expected, raw := test[0], test[1], test[2]
-		reader := bytes.NewReader([]byte(raw))
-		headers, err := parsePAX(reader)
-		if err != nil {
-			t.Errorf("Couldn't parse correctly formatted headers: %v", err)
-			continue
-		}
-		if strings.EqualFold(headers[key], expected) {
-			t.Errorf("mtime header incorrectly parsed: got %s, wanted %s", headers[key], expected)
-			continue
-		}
-		trailer := make([]byte, 100)
-		n, err := reader.Read(trailer)
-		if err != io.EOF || n != 0 {
-			t.Error("Buffer wasn't consumed")
-		}
-	}
-	badHeaderTests := [][]byte{
-		[]byte("3 somelongkey=\n"),
-		[]byte("50 tooshort=\n"),
-	}
-	for _, test := range badHeaderTests {
-		if _, err := parsePAX(bytes.NewReader(test)); err != ErrHeader {
-			t.Fatal("Unexpected success when parsing bad header")
-		}
-	}
-}
-
-func TestParsePAXTime(t *testing.T) {
-	// Some valid PAX time values
-	timestamps := map[string]time.Time{
-		"1350244992.023960108":  time.Unix(1350244992, 23960108), // The common case
-		"1350244992.02396010":   time.Unix(1350244992, 23960100), // Lower precision value
-		"1350244992.0239601089": time.Unix(1350244992, 23960108), // Higher precision value
-		"1350244992":            time.Unix(1350244992, 0),        // Low precision value
-	}
-	for input, expected := range timestamps {
-		ts, err := parsePAXTime(input)
-		if err != nil {
-			t.Fatal(err)
-		}
-		if !ts.Equal(expected) {
-			t.Fatalf("Time parsing failure %s %s", ts, expected)
-		}
-	}
-}
-
-func TestMergePAX(t *testing.T) {
-	hdr := new(Header)
-	// Test a string, integer, and time based value.
-	headers := map[string]string{
-		"path":  "a/b/c",
-		"uid":   "1000",
-		"mtime": "1350244992.023960108",
-	}
-	err := mergePAX(hdr, headers)
-	if err != nil {
-		t.Fatal(err)
-	}
-	want := &Header{
-		Name:    "a/b/c",
-		Uid:     1000,
-		ModTime: time.Unix(1350244992, 23960108),
-	}
-	if !reflect.DeepEqual(hdr, want) {
-		t.Errorf("incorrect merge: got %+v, want %+v", hdr, want)
-	}
-}
-
 func TestSparseFileReader(t *testing.T) {
 	var vectors = []struct {
 		realSize   int64         // Real size of the output file
@@ -1035,116 +960,78 @@ func TestReadHeaderOnly(t *testing.T) {
 	}
 }
 
-func TestParsePAXRecord(t *testing.T) {
-	var medName = strings.Repeat("CD", 50)
-	var longName = strings.Repeat("AB", 100)
+func TestMergePAX(t *testing.T) {
+	vectors := []struct {
+		in   map[string]string
+		want *Header
+		ok   bool
+	}{{
+		in: map[string]string{
+			"path":  "a/b/c",
+			"uid":   "1000",
+			"mtime": "1350244992.023960108",
+		},
+		want: &Header{
+			Name:    "a/b/c",
+			Uid:     1000,
+			ModTime: time.Unix(1350244992, 23960108),
+		},
+		ok: true,
+	}, {
+		in: map[string]string{
+			"gid": "gtgergergersagersgers",
+		},
+	}, {
+		in: map[string]string{
+			"missing":          "missing",
+			"SCHILY.xattr.key": "value",
+		},
+		want: &Header{
+			Xattrs: map[string]string{"key": "value"},
+		},
+		ok: true,
+	}}
 
-	var vectors = []struct {
-		input     string
-		residual  string
-		outputKey string
-		outputVal string
-		ok        bool
-	}{
-		{"6 k=v\n\n", "\n", "k", "v", true},
-		{"19 path=/etc/hosts\n", "", "path", "/etc/hosts", true},
-		{"210 path=" + longName + "\nabc", "abc", "path", longName, true},
-		{"110 path=" + medName + "\n", "", "path", medName, true},
-		{"9 foo=ba\n", "", "foo", "ba", true},
-		{"11 foo=bar\n\x00", "\x00", "foo", "bar", true},
-		{"18 foo=b=\nar=\n==\x00\n", "", "foo", "b=\nar=\n==\x00", true},
-		{"27 foo=hello9 foo=ba\nworld\n", "", "foo", "hello9 foo=ba\nworld", true},
-		{"27 ☺☻☹=日a本b語ç\nmeow mix", "meow mix", "☺☻☹", "日a本b語ç", true},
-		{"17 \x00hello=\x00world\n", "", "\x00hello", "\x00world", true},
-		{"1 k=1\n", "1 k=1\n", "", "", false},
-		{"6 k~1\n", "6 k~1\n", "", "", false},
-		{"6_k=1\n", "6_k=1\n", "", "", false},
-		{"6 k=1 ", "6 k=1 ", "", "", false},
-		{"632 k=1\n", "632 k=1\n", "", "", false},
-		{"16 longkeyname=hahaha\n", "16 longkeyname=hahaha\n", "", "", false},
-		{"3 somelongkey=\n", "3 somelongkey=\n", "", "", false},
-		{"50 tooshort=\n", "50 tooshort=\n", "", "", false},
-	}
-
-	for _, v := range vectors {
-		key, val, res, err := parsePAXRecord(v.input)
-		ok := (err == nil)
-		if v.ok != ok {
-			if v.ok {
-				t.Errorf("parsePAXRecord(%q): got parsing failure, want success", v.input)
-			} else {
-				t.Errorf("parsePAXRecord(%q): got parsing success, want failure", v.input)
-			}
+	for i, v := range vectors {
+		got := new(Header)
+		err := mergePAX(got, v.in)
+		if v.ok && !reflect.DeepEqual(*got, *v.want) {
+			t.Errorf("test %d, mergePAX(...):\ngot  %+v\nwant %+v", i, *got, *v.want)
 		}
-		if ok && (key != v.outputKey || val != v.outputVal) {
-			t.Errorf("parsePAXRecord(%q): got (%q: %q), want (%q: %q)",
-				v.input, key, val, v.outputKey, v.outputVal)
-		}
-		if res != v.residual {
-			t.Errorf("parsePAXRecord(%q): got residual %q, want residual %q",
-				v.input, res, v.residual)
+		if ok := err == nil; ok != v.ok {
+			t.Errorf("test %d, mergePAX(...): got %v, want %v", i, ok, v.ok)
 		}
 	}
 }
 
-func TestParseNumeric(t *testing.T) {
-	var vectors = []struct {
-		input  string
-		output int64
-		ok     bool
+func TestParsePAX(t *testing.T) {
+	vectors := []struct {
+		in   string
+		want map[string]string
+		ok   bool
 	}{
-		// Test base-256 (binary) encoded values.
-		{"", 0, true},
-		{"\x80", 0, true},
-		{"\x80\x00", 0, true},
-		{"\x80\x00\x00", 0, true},
-		{"\xbf", (1 << 6) - 1, true},
-		{"\xbf\xff", (1 << 14) - 1, true},
-		{"\xbf\xff\xff", (1 << 22) - 1, true},
-		{"\xff", -1, true},
-		{"\xff\xff", -1, true},
-		{"\xff\xff\xff", -1, true},
-		{"\xc0", -1 * (1 << 6), true},
-		{"\xc0\x00", -1 * (1 << 14), true},
-		{"\xc0\x00\x00", -1 * (1 << 22), true},
-		{"\x87\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
-		{"\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
-		{"\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
-		{"\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
-		{"\x80\x7f\xff\xff\xff\xff\xff\xff\xff", math.MaxInt64, true},
-		{"\x80\x80\x00\x00\x00\x00\x00\x00\x00", 0, false},
-		{"\xff\x80\x00\x00\x00\x00\x00\x00\x00", math.MinInt64, true},
-		{"\xff\x7f\xff\xff\xff\xff\xff\xff\xff", 0, false},
-		{"\xf5\xec\xd1\xc7\x7e\x5f\x26\x48\x81\x9f\x8f\x9b", 0, false},
-
-		// Test base-8 (octal) encoded values.
-		{"0000000\x00", 0, true},
-		{" \x0000000\x00", 0, true},
-		{" \x0000003\x00", 3, true},
-		{"00000000227\x00", 0227, true},
-		{"032033\x00 ", 032033, true},
-		{"320330\x00 ", 0320330, true},
-		{"0000660\x00 ", 0660, true},
-		{"\x00 0000660\x00 ", 0660, true},
-		{"0123456789abcdef", 0, false},
-		{"0123456789\x00abcdef", 0, false},
-		{"01234567\x0089abcdef", 342391, true},
-		{"0123\x7e\x5f\x264123", 0, false},
+		{"", nil, true},
+		{"6 k=1\n", map[string]string{"k": "1"}, true},
+		{"10 a=name\n", map[string]string{"a": "name"}, true},
+		{"9 a=name\n", map[string]string{"a": "name"}, true},
+		{"30 mtime=1350244992.023960108\n", map[string]string{"mtime": "1350244992.023960108"}, true},
+		{"3 somelongkey=\n", nil, false},
+		{"50 tooshort=\n", nil, false},
+		{"23 GNU.sparse.offset=0\n25 GNU.sparse.numbytes=1\n" +
+			"23 GNU.sparse.offset=2\n25 GNU.sparse.numbytes=3\n",
+			map[string]string{"GNU.sparse.map": "0,1,2,3"}, true},
+		{"13 key1=haha\n13 key2=nana\n13 key3=kaka\n",
+			map[string]string{"key1": "haha", "key2": "nana", "key3": "kaka"}, true},
 	}
 
-	for _, v := range vectors {
-		var p parser
-		num := p.parseNumeric([]byte(v.input))
-		ok := (p.err == nil)
-		if v.ok != ok {
-			if v.ok {
-				t.Errorf("parseNumeric(%q): got parsing failure, want success", v.input)
-			} else {
-				t.Errorf("parseNumeric(%q): got parsing success, want failure", v.input)
-			}
+	for i, v := range vectors {
+		r := strings.NewReader(v.in)
+		got, err := parsePAX(r)
+		if !reflect.DeepEqual(got, v.want) && !(len(got) == 0 && len(v.want) == 0) {
+			t.Errorf("test %d, parsePAX(...):\ngot  %v\nwant %v", i, got, v.want)
 		}
-		if ok && num != v.output {
-			t.Errorf("parseNumeric(%q): got %d, want %d", v.input, num, v.output)
+		if ok := err == nil; ok != v.ok {
+			t.Errorf("test %d, parsePAX(...): got %v, want %v", i, ok, v.ok)
 		}
 	}
 }
diff --git a/src/archive/tar/strconv.go b/src/archive/tar/strconv.go
new file mode 100644
index 0000000000..2619bcdde4
--- /dev/null
+++ b/src/archive/tar/strconv.go
@@ -0,0 +1,254 @@
+// Copyright 2016 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 tar
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const maxNanoSecondIntSize = 9
+
+func isASCII(s string) bool {
+	for _, c := range s {
+		if c >= 0x80 {
+			return false
+		}
+	}
+	return true
+}
+
+func toASCII(s string) string {
+	if isASCII(s) {
+		return s
+	}
+	var buf bytes.Buffer
+	for _, c := range s {
+		if c < 0x80 {
+			buf.WriteByte(byte(c))
+		}
+	}
+	return buf.String()
+}
+
+type parser struct {
+	err error // Last error seen
+}
+
+type formatter struct {
+	err error // Last error seen
+}
+
+// parseString parses bytes as a NUL-terminated C-style string.
+// If a NUL byte is not found then the whole slice is returned as a string.
+func (*parser) parseString(b []byte) string {
+	n := 0
+	for n < len(b) && b[n] != 0 {
+		n++
+	}
+	return string(b[0:n])
+}
+
+// Write s into b, terminating it with a NUL if there is room.
+func (f *formatter) formatString(b []byte, s string) {
+	if len(s) > len(b) {
+		f.err = ErrFieldTooLong
+		return
+	}
+	ascii := toASCII(s)
+	copy(b, ascii)
+	if len(ascii) < len(b) {
+		b[len(ascii)] = 0
+	}
+}
+
+// fitsInBase256 reports whether x can be encoded into n bytes using base-256
+// encoding. Unlike octal encoding, base-256 encoding does not require that the
+// string ends with a NUL character. Thus, all n bytes are available for output.
+//
+// If operating in binary mode, this assumes strict GNU binary mode; which means
+// that the first byte can only be either 0x80 or 0xff. Thus, the first byte is
+// equivalent to the sign bit in two's complement form.
+func fitsInBase256(n int, x int64) bool {
+	var binBits = uint(n-1) * 8
+	return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
+}
+
+// parseNumeric parses the input as being encoded in either base-256 or octal.
+// This function may return negative numbers.
+// If parsing fails or an integer overflow occurs, err will be set.
+func (p *parser) parseNumeric(b []byte) int64 {
+	// Check for base-256 (binary) format first.
+	// If the first bit is set, then all following bits constitute a two's
+	// complement encoded number in big-endian byte order.
+	if len(b) > 0 && b[0]&0x80 != 0 {
+		// Handling negative numbers relies on the following identity:
+		//	-a-1 == ^a
+		//
+		// If the number is negative, we use an inversion mask to invert the
+		// data bytes and treat the value as an unsigned number.
+		var inv byte // 0x00 if positive or zero, 0xff if negative
+		if b[0]&0x40 != 0 {
+			inv = 0xff
+		}
+
+		var x uint64
+		for i, c := range b {
+			c ^= inv // Inverts c only if inv is 0xff, otherwise does nothing
+			if i == 0 {
+				c &= 0x7f // Ignore signal bit in first byte
+			}
+			if (x >> 56) > 0 {
+				p.err = ErrHeader // Integer overflow
+				return 0
+			}
+			x = x<<8 | uint64(c)
+		}
+		if (x >> 63) > 0 {
+			p.err = ErrHeader // Integer overflow
+			return 0
+		}
+		if inv == 0xff {
+			return ^int64(x)
+		}
+		return int64(x)
+	}
+
+	// Normal case is base-8 (octal) format.
+	return p.parseOctal(b)
+}
+
+// Write x into b, as binary (GNUtar/star extension).
+func (f *formatter) formatNumeric(b []byte, x int64) {
+	if fitsInBase256(len(b), x) {
+		for i := len(b) - 1; i >= 0; i-- {
+			b[i] = byte(x)
+			x >>= 8
+		}
+		b[0] |= 0x80 // Highest bit indicates binary format
+		return
+	}
+
+	f.formatOctal(b, 0) // Last resort, just write zero
+	f.err = ErrFieldTooLong
+}
+
+func (p *parser) parseOctal(b []byte) int64 {
+	// Because unused fields are filled with NULs, we need
+	// to skip leading NULs. Fields may also be padded with
+	// spaces or NULs.
+	// So we remove leading and trailing NULs and spaces to
+	// be sure.
+	b = bytes.Trim(b, " \x00")
+
+	if len(b) == 0 {
+		return 0
+	}
+	x, perr := strconv.ParseUint(p.parseString(b), 8, 64)
+	if perr != nil {
+		p.err = ErrHeader
+	}
+	return int64(x)
+}
+
+// Encode x as an octal ASCII string and write it into b with leading zeros.
+func (f *formatter) formatOctal(b []byte, x int64) {
+	s := strconv.FormatInt(x, 8)
+	// leading zeros, but leave room for a NUL.
+	for len(s)+1 < len(b) {
+		s = "0" + s
+	}
+	f.formatString(b, s)
+}
+
+// parsePAXTime takes a string of the form %d.%d as described in
+// the PAX specification.
+func parsePAXTime(t string) (time.Time, error) {
+	buf := []byte(t)
+	pos := bytes.IndexByte(buf, '.')
+	var seconds, nanoseconds int64
+	var err error
+	if pos == -1 {
+		seconds, err = strconv.ParseInt(t, 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+	} else {
+		seconds, err = strconv.ParseInt(string(buf[:pos]), 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+		nanoBuf := string(buf[pos+1:])
+		// Pad as needed before converting to a decimal.
+		// For example .030 -> .030000000 -> 30000000 nanoseconds
+		if len(nanoBuf) < maxNanoSecondIntSize {
+			// Right pad
+			nanoBuf += strings.Repeat("0", maxNanoSecondIntSize-len(nanoBuf))
+		} else if len(nanoBuf) > maxNanoSecondIntSize {
+			// Right truncate
+			nanoBuf = nanoBuf[:maxNanoSecondIntSize]
+		}
+		nanoseconds, err = strconv.ParseInt(nanoBuf, 10, 0)
+		if err != nil {
+			return time.Time{}, err
+		}
+	}
+	ts := time.Unix(seconds, nanoseconds)
+	return ts, nil
+}
+
+// TODO(dsnet): Implement formatPAXTime.
+
+// parsePAXRecord parses the input PAX record string into a key-value pair.
+// If parsing is successful, it will slice off the currently read record and
+// return the remainder as r.
+//
+// A PAX record is of the following form:
+//	"%d %s=%s\n" % (size, key, value)
+func parsePAXRecord(s string) (k, v, r string, err error) {
+	// The size field ends at the first space.
+	sp := strings.IndexByte(s, ' ')
+	if sp == -1 {
+		return "", "", s, ErrHeader
+	}
+
+	// Parse the first token as a decimal integer.
+	n, perr := strconv.ParseInt(s[:sp], 10, 0) // Intentionally parse as native int
+	if perr != nil || n < 5 || int64(len(s)) < n {
+		return "", "", s, ErrHeader
+	}
+
+	// Extract everything between the space and the final newline.
+	rec, nl, rem := s[sp+1:n-1], s[n-1:n], s[n:]
+	if nl != "\n" {
+		return "", "", s, ErrHeader
+	}
+
+	// The first equals separates the key from the value.
+	eq := strings.IndexByte(rec, '=')
+	if eq == -1 {
+		return "", "", s, ErrHeader
+	}
+	return rec[:eq], rec[eq+1:], rem, nil
+}
+
+// formatPAXRecord formats a single PAX record, prefixing it with the
+// appropriate length.
+func formatPAXRecord(k, v string) string {
+	const padding = 3 // Extra padding for ' ', '=', and '\n'
+	size := len(k) + len(v) + padding
+	size += len(strconv.Itoa(size))
+	record := fmt.Sprintf("%d %s=%s\n", size, k, v)
+
+	// Final adjustment if adding size field increased the record size.
+	if len(record) != size {
+		size = len(record)
+		record = fmt.Sprintf("%d %s=%s\n", size, k, v)
+	}
+	return record
+}
diff --git a/src/archive/tar/strconv_test.go b/src/archive/tar/strconv_test.go
new file mode 100644
index 0000000000..7caecb5196
--- /dev/null
+++ b/src/archive/tar/strconv_test.go
@@ -0,0 +1,257 @@
+// Copyright 2016 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 tar
+
+import (
+	"math"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestFitsInBase256(t *testing.T) {
+	vectors := []struct {
+		in    int64
+		width int
+		ok    bool
+	}{
+		{+1, 8, true},
+		{0, 8, true},
+		{-1, 8, true},
+		{1 << 56, 8, false},
+		{(1 << 56) - 1, 8, true},
+		{-1 << 56, 8, true},
+		{(-1 << 56) - 1, 8, false},
+		{121654, 8, true},
+		{-9849849, 8, true},
+		{math.MaxInt64, 9, true},
+		{0, 9, true},
+		{math.MinInt64, 9, true},
+		{math.MaxInt64, 12, true},
+		{0, 12, true},
+		{math.MinInt64, 12, true},
+	}
+
+	for _, v := range vectors {
+		ok := fitsInBase256(v.width, v.in)
+		if ok != v.ok {
+			t.Errorf("fitsInBase256(%d, %d): got %v, want %v", v.in, v.width, ok, v.ok)
+		}
+	}
+}
+
+func TestParseNumeric(t *testing.T) {
+	vectors := []struct {
+		in   string
+		want int64
+		ok   bool
+	}{
+		// Test base-256 (binary) encoded values.
+		{"", 0, true},
+		{"\x80", 0, true},
+		{"\x80\x00", 0, true},
+		{"\x80\x00\x00", 0, true},
+		{"\xbf", (1 << 6) - 1, true},
+		{"\xbf\xff", (1 << 14) - 1, true},
+		{"\xbf\xff\xff", (1 << 22) - 1, true},
+		{"\xff", -1, true},
+		{"\xff\xff", -1, true},
+		{"\xff\xff\xff", -1, true},
+		{"\xc0", -1 * (1 << 6), true},
+		{"\xc0\x00", -1 * (1 << 14), true},
+		{"\xc0\x00\x00", -1 * (1 << 22), true},
+		{"\x87\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
+		{"\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", 537795476381659745, true},
+		{"\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
+		{"\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", -615126028225187231, true},
+		{"\x80\x7f\xff\xff\xff\xff\xff\xff\xff", math.MaxInt64, true},
+		{"\x80\x80\x00\x00\x00\x00\x00\x00\x00", 0, false},
+		{"\xff\x80\x00\x00\x00\x00\x00\x00\x00", math.MinInt64, true},
+		{"\xff\x7f\xff\xff\xff\xff\xff\xff\xff", 0, false},
+		{"\xf5\xec\xd1\xc7\x7e\x5f\x26\x48\x81\x9f\x8f\x9b", 0, false},
+
+		// Test base-8 (octal) encoded values.
+		{"0000000\x00", 0, true},
+		{" \x0000000\x00", 0, true},
+		{" \x0000003\x00", 3, true},
+		{"00000000227\x00", 0227, true},
+		{"032033\x00 ", 032033, true},
+		{"320330\x00 ", 0320330, true},
+		{"0000660\x00 ", 0660, true},
+		{"\x00 0000660\x00 ", 0660, true},
+		{"0123456789abcdef", 0, false},
+		{"0123456789\x00abcdef", 0, false},
+		{"01234567\x0089abcdef", 342391, true},
+		{"0123\x7e\x5f\x264123", 0, false},
+	}
+
+	for _, v := range vectors {
+		var p parser
+		got := p.parseNumeric([]byte(v.in))
+		ok := (p.err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("parseNumeric(%q): got parsing failure, want success", v.in)
+			} else {
+				t.Errorf("parseNumeric(%q): got parsing success, want failure", v.in)
+			}
+		}
+		if ok && got != v.want {
+			t.Errorf("parseNumeric(%q): got %d, want %d", v.in, got, v.want)
+		}
+	}
+}
+
+func TestFormatNumeric(t *testing.T) {
+	vectors := []struct {
+		in   int64
+		want string
+		ok   bool
+	}{
+		// Test base-256 (binary) encoded values.
+		{-1, "\xff", true},
+		{-1, "\xff\xff", true},
+		{-1, "\xff\xff\xff", true},
+		{(1 << 0), "0", false},
+		{(1 << 8) - 1, "\x80\xff", true},
+		{(1 << 8), "0\x00", false},
+		{(1 << 16) - 1, "\x80\xff\xff", true},
+		{(1 << 16), "00\x00", false},
+		{-1 * (1 << 0), "\xff", true},
+		{-1*(1<<0) - 1, "0", false},
+		{-1 * (1 << 8), "\xff\x00", true},
+		{-1*(1<<8) - 1, "0\x00", false},
+		{-1 * (1 << 16), "\xff\x00\x00", true},
+		{-1*(1<<16) - 1, "00\x00", false},
+		{537795476381659745, "0000000\x00", false},
+		{537795476381659745, "\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", true},
+		{-615126028225187231, "0000000\x00", false},
+		{-615126028225187231, "\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", true},
+		{math.MaxInt64, "0000000\x00", false},
+		{math.MaxInt64, "\x80\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff", true},
+		{math.MinInt64, "0000000\x00", false},
+		{math.MinInt64, "\xff\xff\xff\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
+		{math.MaxInt64, "\x80\x7f\xff\xff\xff\xff\xff\xff\xff", true},
+		{math.MinInt64, "\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
+	}
+
+	for _, v := range vectors {
+		var f formatter
+		got := make([]byte, len(v.want))
+		f.formatNumeric(got, v.in)
+		ok := (f.err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("formatNumeric(%d): got formatting failure, want success", v.in)
+			} else {
+				t.Errorf("formatNumeric(%d): got formatting success, want failure", v.in)
+			}
+		}
+		if string(got) != v.want {
+			t.Errorf("formatNumeric(%d): got %q, want %q", v.in, got, v.want)
+		}
+	}
+}
+
+func TestParsePAXTime(t *testing.T) {
+	timestamps := map[string]time.Time{
+		"1350244992.023960108":  time.Unix(1350244992, 23960108), // The common case
+		"1350244992.02396010":   time.Unix(1350244992, 23960100), // Lower precision value
+		"1350244992.0239601089": time.Unix(1350244992, 23960108), // Higher precision value
+		"1350244992":            time.Unix(1350244992, 0),        // Low precision value
+	}
+
+	for input, expected := range timestamps {
+		ts, err := parsePAXTime(input)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !ts.Equal(expected) {
+			t.Fatalf("Time parsing failure %s %s", ts, expected)
+		}
+	}
+}
+
+func TestParsePAXRecord(t *testing.T) {
+	medName := strings.Repeat("CD", 50)
+	longName := strings.Repeat("AB", 100)
+
+	vectors := []struct {
+		in      string
+		wantRes string
+		wantKey string
+		wantVal string
+		ok      bool
+	}{
+		{"6 k=v\n\n", "\n", "k", "v", true},
+		{"19 path=/etc/hosts\n", "", "path", "/etc/hosts", true},
+		{"210 path=" + longName + "\nabc", "abc", "path", longName, true},
+		{"110 path=" + medName + "\n", "", "path", medName, true},
+		{"9 foo=ba\n", "", "foo", "ba", true},
+		{"11 foo=bar\n\x00", "\x00", "foo", "bar", true},
+		{"18 foo=b=\nar=\n==\x00\n", "", "foo", "b=\nar=\n==\x00", true},
+		{"27 foo=hello9 foo=ba\nworld\n", "", "foo", "hello9 foo=ba\nworld", true},
+		{"27 ☺☻☹=日a本b語ç\nmeow mix", "meow mix", "☺☻☹", "日a本b語ç", true},
+		{"17 \x00hello=\x00world\n", "", "\x00hello", "\x00world", true},
+		{"1 k=1\n", "1 k=1\n", "", "", false},
+		{"6 k~1\n", "6 k~1\n", "", "", false},
+		{"6_k=1\n", "6_k=1\n", "", "", false},
+		{"6 k=1 ", "6 k=1 ", "", "", false},
+		{"632 k=1\n", "632 k=1\n", "", "", false},
+		{"16 longkeyname=hahaha\n", "16 longkeyname=hahaha\n", "", "", false},
+		{"3 somelongkey=\n", "3 somelongkey=\n", "", "", false},
+		{"50 tooshort=\n", "50 tooshort=\n", "", "", false},
+	}
+
+	for _, v := range vectors {
+		key, val, res, err := parsePAXRecord(v.in)
+		ok := (err == nil)
+		if ok != v.ok {
+			if v.ok {
+				t.Errorf("parsePAXRecord(%q): got parsing failure, want success", v.in)
+			} else {
+				t.Errorf("parsePAXRecord(%q): got parsing success, want failure", v.in)
+			}
+		}
+		if v.ok && (key != v.wantKey || val != v.wantVal) {
+			t.Errorf("parsePAXRecord(%q): got (%q: %q), want (%q: %q)",
+				v.in, key, val, v.wantKey, v.wantVal)
+		}
+		if res != v.wantRes {
+			t.Errorf("parsePAXRecord(%q): got residual %q, want residual %q",
+				v.in, res, v.wantRes)
+		}
+	}
+}
+
+func TestFormatPAXRecord(t *testing.T) {
+	medName := strings.Repeat("CD", 50)
+	longName := strings.Repeat("AB", 100)
+
+	vectors := []struct {
+		inKey string
+		inVal string
+		want  string
+	}{
+		{"k", "v", "6 k=v\n"},
+		{"path", "/etc/hosts", "19 path=/etc/hosts\n"},
+		{"path", longName, "210 path=" + longName + "\n"},
+		{"path", medName, "110 path=" + medName + "\n"},
+		{"foo", "ba", "9 foo=ba\n"},
+		{"foo", "bar", "11 foo=bar\n"},
+		{"foo", "b=\nar=\n==\x00", "18 foo=b=\nar=\n==\x00\n"},
+		{"foo", "hello9 foo=ba\nworld", "27 foo=hello9 foo=ba\nworld\n"},
+		{"☺☻☹", "日a本b語ç", "27 ☺☻☹=日a本b語ç\n"},
+		{"\x00hello", "\x00world", "17 \x00hello=\x00world\n"},
+	}
+
+	for _, v := range vectors {
+		got := formatPAXRecord(v.inKey, v.inVal)
+		if got != v.want {
+			t.Errorf("formatPAXRecord(%q, %q): got %q, want %q",
+				v.inKey, v.inVal, got, v.want)
+		}
+	}
+}
diff --git a/src/archive/tar/writer.go b/src/archive/tar/writer.go
index 6acc055ca4..bd6e7e5b58 100644
--- a/src/archive/tar/writer.go
+++ b/src/archive/tar/writer.go
@@ -42,10 +42,6 @@ type Writer struct {
 	paxHdrBuff block // buffer to use in writeHeader when writing a PAX header
 }
 
-type formatter struct {
-	err error // Last error seen
-}
-
 // NewWriter creates a new Writer writing to w.
 func NewWriter(w io.Writer) *Writer { return &Writer{w: w} }
 
@@ -71,56 +67,6 @@ func (tw *Writer) Flush() error {
 	return tw.err
 }
 
-// Write s into b, terminating it with a NUL if there is room.
-func (f *formatter) formatString(b []byte, s string) {
-	if len(s) > len(b) {
-		f.err = ErrFieldTooLong
-		return
-	}
-	ascii := toASCII(s)
-	copy(b, ascii)
-	if len(ascii) < len(b) {
-		b[len(ascii)] = 0
-	}
-}
-
-// Encode x as an octal ASCII string and write it into b with leading zeros.
-func (f *formatter) formatOctal(b []byte, x int64) {
-	s := strconv.FormatInt(x, 8)
-	// leading zeros, but leave room for a NUL.
-	for len(s)+1 < len(b) {
-		s = "0" + s
-	}
-	f.formatString(b, s)
-}
-
-// fitsInBase256 reports whether x can be encoded into n bytes using base-256
-// encoding. Unlike octal encoding, base-256 encoding does not require that the
-// string ends with a NUL character. Thus, all n bytes are available for output.
-//
-// If operating in binary mode, this assumes strict GNU binary mode; which means
-// that the first byte can only be either 0x80 or 0xff. Thus, the first byte is
-// equivalent to the sign bit in two's complement form.
-func fitsInBase256(n int, x int64) bool {
-	var binBits = uint(n-1) * 8
-	return n >= 9 || (x >= -1<<binBits && x < 1<<binBits)
-}
-
-// Write x into b, as binary (GNUtar/star extension).
-func (f *formatter) formatNumeric(b []byte, x int64) {
-	if fitsInBase256(len(b), x) {
-		for i := len(b) - 1; i >= 0; i-- {
-			b[i] = byte(x)
-			x >>= 8
-		}
-		b[0] |= 0x80 // Highest bit indicates binary format
-		return
-	}
-
-	f.formatOctal(b, 0) // Last resort, just write zero
-	f.err = ErrFieldTooLong
-}
-
 var (
 	minTime = time.Unix(0, 0)
 	// There is room for 11 octal digits (33 bits) of mtime.
@@ -340,22 +286,6 @@ func (tw *Writer) writePAXHeader(hdr *Header, paxHeaders map[string]string) erro
 	return nil
 }
 
-// formatPAXRecord formats a single PAX record, prefixing it with the
-// appropriate length.
-func formatPAXRecord(k, v string) string {
-	const padding = 3 // Extra padding for ' ', '=', and '\n'
-	size := len(k) + len(v) + padding
-	size += len(strconv.Itoa(size))
-	record := fmt.Sprintf("%d %s=%s\n", size, k, v)
-
-	// Final adjustment if adding size field increased the record size.
-	if len(record) != size {
-		size = len(record)
-		record = fmt.Sprintf("%d %s=%s\n", size, k, v)
-	}
-	return record
-}
-
 // Write writes to the current entry in the tar archive.
 // Write returns the error ErrWriteTooLong if more than
 // hdr.Size bytes are written after WriteHeader.
diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
index 27aa8e5dab..a4f3f4e43d 100644
--- a/src/archive/tar/writer_test.go
+++ b/src/archive/tar/writer_test.go
@@ -9,7 +9,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"math"
 	"os"
 	"reflect"
 	"sort"
@@ -608,115 +607,3 @@ func TestSplitUSTARPath(t *testing.T) {
 		}
 	}
 }
-
-func TestFormatPAXRecord(t *testing.T) {
-	var medName = strings.Repeat("CD", 50)
-	var longName = strings.Repeat("AB", 100)
-
-	var vectors = []struct {
-		inputKey string
-		inputVal string
-		output   string
-	}{
-		{"k", "v", "6 k=v\n"},
-		{"path", "/etc/hosts", "19 path=/etc/hosts\n"},
-		{"path", longName, "210 path=" + longName + "\n"},
-		{"path", medName, "110 path=" + medName + "\n"},
-		{"foo", "ba", "9 foo=ba\n"},
-		{"foo", "bar", "11 foo=bar\n"},
-		{"foo", "b=\nar=\n==\x00", "18 foo=b=\nar=\n==\x00\n"},
-		{"foo", "hello9 foo=ba\nworld", "27 foo=hello9 foo=ba\nworld\n"},
-		{"☺☻☹", "日a本b語ç", "27 ☺☻☹=日a本b語ç\n"},
-		{"\x00hello", "\x00world", "17 \x00hello=\x00world\n"},
-	}
-
-	for _, v := range vectors {
-		output := formatPAXRecord(v.inputKey, v.inputVal)
-		if output != v.output {
-			t.Errorf("formatPAXRecord(%q, %q): got %q, want %q",
-				v.inputKey, v.inputVal, output, v.output)
-		}
-	}
-}
-
-func TestFitsInBase256(t *testing.T) {
-	var vectors = []struct {
-		input int64
-		width int
-		ok    bool
-	}{
-		{+1, 8, true},
-		{0, 8, true},
-		{-1, 8, true},
-		{1 << 56, 8, false},
-		{(1 << 56) - 1, 8, true},
-		{-1 << 56, 8, true},
-		{(-1 << 56) - 1, 8, false},
-		{121654, 8, true},
-		{-9849849, 8, true},
-		{math.MaxInt64, 9, true},
-		{0, 9, true},
-		{math.MinInt64, 9, true},
-		{math.MaxInt64, 12, true},
-		{0, 12, true},
-		{math.MinInt64, 12, true},
-	}
-
-	for _, v := range vectors {
-		ok := fitsInBase256(v.width, v.input)
-		if ok != v.ok {
-			t.Errorf("checkNumeric(%d, %d): got %v, want %v", v.input, v.width, ok, v.ok)
-		}
-	}
-}
-
-func TestFormatNumeric(t *testing.T) {
-	var vectors = []struct {
-		input  int64
-		output string
-		ok     bool
-	}{
-		// Test base-256 (binary) encoded values.
-		{-1, "\xff", true},
-		{-1, "\xff\xff", true},
-		{-1, "\xff\xff\xff", true},
-		{(1 << 0), "0", false},
-		{(1 << 8) - 1, "\x80\xff", true},
-		{(1 << 8), "0\x00", false},
-		{(1 << 16) - 1, "\x80\xff\xff", true},
-		{(1 << 16), "00\x00", false},
-		{-1 * (1 << 0), "\xff", true},
-		{-1*(1<<0) - 1, "0", false},
-		{-1 * (1 << 8), "\xff\x00", true},
-		{-1*(1<<8) - 1, "0\x00", false},
-		{-1 * (1 << 16), "\xff\x00\x00", true},
-		{-1*(1<<16) - 1, "00\x00", false},
-		{537795476381659745, "0000000\x00", false},
-		{537795476381659745, "\x80\x00\x00\x00\x07\x76\xa2\x22\xeb\x8a\x72\x61", true},
-		{-615126028225187231, "0000000\x00", false},
-		{-615126028225187231, "\xff\xff\xff\xff\xf7\x76\xa2\x22\xeb\x8a\x72\x61", true},
-		{math.MaxInt64, "0000000\x00", false},
-		{math.MaxInt64, "\x80\x00\x00\x00\x7f\xff\xff\xff\xff\xff\xff\xff", true},
-		{math.MinInt64, "0000000\x00", false},
-		{math.MinInt64, "\xff\xff\xff\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
-		{math.MaxInt64, "\x80\x7f\xff\xff\xff\xff\xff\xff\xff", true},
-		{math.MinInt64, "\xff\x80\x00\x00\x00\x00\x00\x00\x00", true},
-	}
-
-	for _, v := range vectors {
-		var f formatter
-		output := make([]byte, len(v.output))
-		f.formatNumeric(output, v.input)
-		ok := (f.err == nil)
-		if ok != v.ok {
-			if v.ok {
-				t.Errorf("formatNumeric(%d): got formatting failure, want success", v.input)
-			} else {
-				t.Errorf("formatNumeric(%d): got formatting success, want failure", v.input)
-			}
-		}
-		if string(output) != v.output {
-			t.Errorf("formatNumeric(%d): got %q, want %q", v.input, output, v.output)
-		}
-	}
-}