libgo: Update to weekly.2011-11-02.

From-SVN: r181964

17 files changed, 103 insertions, 112 deletions

diff --git a/libgo/go/image/bmp/reader.go b/libgo/go/image/bmp/reader.go
index 134de5b..ad56865 100644
--- a/libgo/go/image/bmp/reader.go
+++ b/libgo/go/image/bmp/reader.go
@@ -8,15 +8,15 @@
 package bmp
 
 import (
+	"errors"
 	"image/color"
 	"image"
 	"io"
-	"os"
 )
 
 // ErrUnsupported means that the input BMP image uses a valid but unsupported
 // feature.
-var ErrUnsupported = os.NewError("bmp: unsupported BMP image")
+var ErrUnsupported = errors.New("bmp: unsupported BMP image")
 
 func readUint16(b []byte) uint16 {
 	return uint16(b[0]) | uint16(b[1])<<8
@@ -27,7 +27,7 @@ func readUint32(b []byte) uint32 {
 }
 
 // decodePaletted reads an 8 bit-per-pixel BMP image from r.
-func decodePaletted(r io.Reader, c image.Config) (image.Image, os.Error) {
+func decodePaletted(r io.Reader, c image.Config) (image.Image, error) {
 	var tmp [4]byte
 	paletted := image.NewPaletted(image.Rect(0, 0, c.Width, c.Height), c.ColorModel.(color.Palette))
 	// BMP images are stored bottom-up rather than top-down.
@@ -49,7 +49,7 @@ func decodePaletted(r io.Reader, c image.Config) (image.Image, os.Error) {
 }
 
 // decodeRGBA reads a 24 bit-per-pixel BMP image from r.
-func decodeRGBA(r io.Reader, c image.Config) (image.Image, os.Error) {
+func decodeRGBA(r io.Reader, c image.Config) (image.Image, error) {
 	rgba := image.NewRGBA(image.Rect(0, 0, c.Width, c.Height))
 	// There are 3 bytes per pixel, and each row is 4-byte aligned.
 	b := make([]byte, (3*c.Width+3)&^3)
@@ -73,7 +73,7 @@ func decodeRGBA(r io.Reader, c image.Config) (image.Image, os.Error) {
 
 // Decode reads a BMP image from r and returns it as an image.Image.
 // Limitation: The file must be 8 or 24 bits per pixel.
-func Decode(r io.Reader) (image.Image, os.Error) {
+func Decode(r io.Reader) (image.Image, error) {
 	c, err := DecodeConfig(r)
 	if err != nil {
 		return nil, err
@@ -87,7 +87,7 @@ func Decode(r io.Reader) (image.Image, os.Error) {
 // DecodeConfig returns the color model and dimensions of a BMP image without
 // decoding the entire image.
 // Limitation: The file must be 8 or 24 bits per pixel.
-func DecodeConfig(r io.Reader) (config image.Config, err os.Error) {
+func DecodeConfig(r io.Reader) (config image.Config, err error) {
 	// We only support those BMP images that are a BITMAPFILEHEADER
 	// immediately followed by a BITMAPINFOHEADER.
 	const (
@@ -99,7 +99,7 @@ func DecodeConfig(r io.Reader) (config image.Config, err os.Error) {
 		return
 	}
 	if string(b[:2]) != "BM" {
-		err = os.NewError("bmp: invalid format")
+		err = errors.New("bmp: invalid format")
 		return
 	}
 	offset := readUint32(b[10:14])
diff --git a/libgo/go/image/decode_test.go b/libgo/go/image/decode_test.go
index b348c1d..1b7db8b 100644
--- a/libgo/go/image/decode_test.go
+++ b/libgo/go/image/decode_test.go
@@ -41,7 +41,7 @@ var imageTests = []imageTest{
 	{"testdata/video-005.gray.png", "testdata/video-005.gray.png", 0},
 }
 
-func decode(filename string) (image.Image, string, os.Error) {
+func decode(filename string) (image.Image, string, error) {
 	f, err := os.Open(filename)
 	if err != nil {
 		return nil, "", err
@@ -50,7 +50,7 @@ func decode(filename string) (image.Image, string, os.Error) {
 	return image.Decode(bufio.NewReader(f))
 }
 
-func decodeConfig(filename string) (image.Config, string, os.Error) {
+func decodeConfig(filename string) (image.Config, string, error) {
 	f, err := os.Open(filename)
 	if err != nil {
 		return image.Config{}, "", err
@@ -83,7 +83,7 @@ loop:
 	for _, it := range imageTests {
 		g := golden[it.goldenFilename]
 		if g == nil {
-			var err os.Error
+			var err error
 			g, _, err = decode(it.goldenFilename)
 			if err != nil {
 				t.Errorf("%s: %v", it.goldenFilename, err)
diff --git a/libgo/go/image/format.go b/libgo/go/image/format.go
index b485932..78fc3ed 100644
--- a/libgo/go/image/format.go
+++ b/libgo/go/image/format.go
@@ -6,18 +6,18 @@ package image
 
 import (
 	"bufio"
+	"errors"
 	"io"
-	"os"
 )
 
 // An UnknownFormatErr indicates that decoding encountered an unknown format.
-var UnknownFormatErr = os.NewError("image: unknown format")
+var UnknownFormatErr = errors.New("image: unknown format")
 
 // A format holds an image format's name, magic header and how to decode it.
 type format struct {
 	name, magic  string
-	decode       func(io.Reader) (Image, os.Error)
-	decodeConfig func(io.Reader) (Config, os.Error)
+	decode       func(io.Reader) (Image, error)
+	decodeConfig func(io.Reader) (Config, error)
 }
 
 // Formats is the list of registered formats.
@@ -29,14 +29,14 @@ var formats []format
 // string can contain "?" wildcards that each match any one byte.
 // Decode is the function that decodes the encoded image.
 // DecodeConfig is the function that decodes just its configuration.
-func RegisterFormat(name, magic string, decode func(io.Reader) (Image, os.Error), decodeConfig func(io.Reader) (Config, os.Error)) {
+func RegisterFormat(name, magic string, decode func(io.Reader) (Image, error), decodeConfig func(io.Reader) (Config, error)) {
 	formats = append(formats, format{name, magic, decode, decodeConfig})
 }
 
 // A reader is an io.Reader that can also peek ahead.
 type reader interface {
 	io.Reader
-	Peek(int) ([]byte, os.Error)
+	Peek(int) ([]byte, error)
 }
 
 // AsReader converts an io.Reader to a reader.
@@ -75,7 +75,7 @@ func sniff(r reader) format {
 // The string returned is the format name used during format registration.
 // Format registration is typically done by the init method of the codec-
 // specific package.
-func Decode(r io.Reader) (Image, string, os.Error) {
+func Decode(r io.Reader) (Image, string, error) {
 	rr := asReader(r)
 	f := sniff(rr)
 	if f.decode == nil {
@@ -89,7 +89,7 @@ func Decode(r io.Reader) (Image, string, os.Error) {
 // been encoded in a registered format. The string returned is the format name
 // used during format registration. Format registration is typically done by
 // the init method of the codec-specific package.
-func DecodeConfig(r io.Reader) (Config, string, os.Error) {
+func DecodeConfig(r io.Reader) (Config, string, error) {
 	rr := asReader(r)
 	f := sniff(rr)
 	if f.decodeConfig == nil {
diff --git a/libgo/go/image/gif/reader.go b/libgo/go/image/gif/reader.go
index a5a4265..24b53c5 100644
--- a/libgo/go/image/gif/reader.go
+++ b/libgo/go/image/gif/reader.go
@@ -10,11 +10,11 @@ package gif
 import (
 	"bufio"
 	"compress/lzw"
+	"errors"
 	"fmt"
 	"image"
 	"image/color"
 	"io"
-	"os"
 )
 
 // If the io.Reader does not also have ReadByte, then decode will introduce its own buffering.
@@ -97,7 +97,7 @@ type blockReader struct {
 	tmp   [256]byte
 }
 
-func (b *blockReader) Read(p []byte) (int, os.Error) {
+func (b *blockReader) Read(p []byte) (int, error) {
 	if len(p) == 0 {
 		return 0, nil
 	}
@@ -107,7 +107,7 @@ func (b *blockReader) Read(p []byte) (int, os.Error) {
 			return 0, err
 		}
 		if blockLen == 0 {
-			return 0, os.EOF
+			return 0, io.EOF
 		}
 		b.slice = b.tmp[0:blockLen]
 		if _, err = io.ReadFull(b.r, b.slice); err != nil {
@@ -120,7 +120,7 @@ func (b *blockReader) Read(p []byte) (int, os.Error) {
 }
 
 // decode reads a GIF image from r and stores the result in d.
-func (d *decoder) decode(r io.Reader, configOnly bool) os.Error {
+func (d *decoder) decode(r io.Reader, configOnly bool) error {
 	// Add buffering if r does not provide ReadByte.
 	if rr, ok := r.(reader); ok {
 		d.r = rr
@@ -146,7 +146,7 @@ Loop:
 	for err == nil {
 		var c byte
 		c, err = d.r.ReadByte()
-		if err == os.EOF {
+		if err == io.EOF {
 			break
 		}
 		switch c {
@@ -189,7 +189,7 @@ Loop:
 				return err
 			}
 			if c != 0 {
-				return os.NewError("gif: extra data after image")
+				return errors.New("gif: extra data after image")
 			}
 
 			// Undo the interlacing if necessary.
@@ -217,7 +217,7 @@ Loop:
 	return nil
 }
 
-func (d *decoder) readHeaderAndScreenDescriptor() os.Error {
+func (d *decoder) readHeaderAndScreenDescriptor() error {
 	_, err := io.ReadFull(d.r, d.tmp[0:13])
 	if err != nil {
 		return err
@@ -236,7 +236,7 @@ func (d *decoder) readHeaderAndScreenDescriptor() os.Error {
 	return nil
 }
 
-func (d *decoder) readColorMap() (color.Palette, os.Error) {
+func (d *decoder) readColorMap() (color.Palette, error) {
 	if d.pixelSize > 8 {
 		return nil, fmt.Errorf("gif: can't handle %d bits per pixel", d.pixelSize)
 	}
@@ -258,7 +258,7 @@ func (d *decoder) readColorMap() (color.Palette, os.Error) {
 	return colorMap, nil
 }
 
-func (d *decoder) readExtension() os.Error {
+func (d *decoder) readExtension() error {
 	extension, err := d.r.ReadByte()
 	if err != nil {
 		return err
@@ -307,7 +307,7 @@ func (d *decoder) readExtension() os.Error {
 	panic("unreachable")
 }
 
-func (d *decoder) readGraphicControl() os.Error {
+func (d *decoder) readGraphicControl() error {
 	if _, err := io.ReadFull(d.r, d.tmp[0:6]); err != nil {
 		return fmt.Errorf("gif: can't read graphic control: %s", err)
 	}
@@ -326,7 +326,7 @@ func (d *decoder) setTransparency(colorMap color.Palette) {
 	}
 }
 
-func (d *decoder) newImageFromDescriptor() (*image.Paletted, os.Error) {
+func (d *decoder) newImageFromDescriptor() (*image.Paletted, error) {
 	if _, err := io.ReadFull(d.r, d.tmp[0:9]); err != nil {
 		return nil, fmt.Errorf("gif: can't read image descriptor: %s", err)
 	}
@@ -338,7 +338,7 @@ func (d *decoder) newImageFromDescriptor() (*image.Paletted, os.Error) {
 	return image.NewPaletted(image.Rect(left, top, left+width, top+height), nil), nil
 }
 
-func (d *decoder) readBlock() (int, os.Error) {
+func (d *decoder) readBlock() (int, error) {
 	n, err := d.r.ReadByte()
 	if n == 0 || err != nil {
 		return 0, err
@@ -379,7 +379,7 @@ func uninterlace(m *image.Paletted) {
 
 // Decode reads a GIF image from r and returns the first embedded
 // image as an image.Image.
-func Decode(r io.Reader) (image.Image, os.Error) {
+func Decode(r io.Reader) (image.Image, error) {
 	var d decoder
 	if err := d.decode(r, false); err != nil {
 		return nil, err
@@ -396,7 +396,7 @@ type GIF struct {
 
 // DecodeAll reads a GIF image from r and returns the sequential frames
 // and timing information.
-func DecodeAll(r io.Reader) (*GIF, os.Error) {
+func DecodeAll(r io.Reader) (*GIF, error) {
 	var d decoder
 	if err := d.decode(r, false); err != nil {
 		return nil, err
@@ -411,7 +411,7 @@ func DecodeAll(r io.Reader) (*GIF, os.Error) {
 
 // DecodeConfig returns the global color model and dimensions of a GIF image
 // without decoding the entire image.
-func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+func DecodeConfig(r io.Reader) (image.Config, error) {
 	var d decoder
 	if err := d.decode(r, true); err != nil {
 		return image.Config{}, err
diff --git a/libgo/go/image/jpeg/huffman.go b/libgo/go/image/jpeg/huffman.go
index 0d03a73..d238249 100644
--- a/libgo/go/image/jpeg/huffman.go
+++ b/libgo/go/image/jpeg/huffman.go
@@ -4,10 +4,7 @@
 
 package jpeg
 
-import (
-	"io"
-	"os"
-)
+import "io"
 
 // Each code is at most 16 bits long.
 const maxCodeLength = 16
@@ -36,7 +33,7 @@ type huffman struct {
 }
 
 // Reads bytes from the io.Reader to ensure that bits.n is at least n.
-func (d *decoder) ensureNBits(n int) os.Error {
+func (d *decoder) ensureNBits(n int) error {
 	for d.b.n < n {
 		c, err := d.r.ReadByte()
 		if err != nil {
@@ -64,7 +61,7 @@ func (d *decoder) ensureNBits(n int) os.Error {
 }
 
 // The composition of RECEIVE and EXTEND, specified in section F.2.2.1.
-func (d *decoder) receiveExtend(t uint8) (int, os.Error) {
+func (d *decoder) receiveExtend(t uint8) (int, error) {
 	err := d.ensureNBits(int(t))
 	if err != nil {
 		return 0, err
@@ -81,7 +78,7 @@ func (d *decoder) receiveExtend(t uint8) (int, os.Error) {
 
 // Processes a Define Huffman Table marker, and initializes a huffman struct from its contents.
 // Specified in section B.2.4.2.
-func (d *decoder) processDHT(n int) os.Error {
+func (d *decoder) processDHT(n int) error {
 	for n > 0 {
 		if n < 17 {
 			return FormatError("DHT has wrong length")
@@ -167,7 +164,7 @@ func (d *decoder) processDHT(n int) os.Error {
 // Returns the next Huffman-coded value from the bit stream, decoded according to h.
 // TODO(nigeltao): This decoding algorithm is simple, but slow. A lookahead table, instead of always
 // peeling off only 1 bit at at time, ought to be faster.
-func (d *decoder) decodeHuffman(h *huffman) (uint8, os.Error) {
+func (d *decoder) decodeHuffman(h *huffman) (uint8, error) {
 	if h.length == 0 {
 		return 0, FormatError("uninitialized Huffman table")
 	}
diff --git a/libgo/go/image/jpeg/reader.go b/libgo/go/image/jpeg/reader.go
index 450355e..c1fc2d5 100644
--- a/libgo/go/image/jpeg/reader.go
+++ b/libgo/go/image/jpeg/reader.go
@@ -13,7 +13,6 @@ import (
 	"image/color"
 	"image/ycbcr"
 	"io"
-	"os"
 )
 
 // TODO(nigeltao): fix up the doc comment style so that sentences start with
@@ -22,12 +21,12 @@ import (
 // A FormatError reports that the input is not a valid JPEG.
 type FormatError string
 
-func (e FormatError) String() string { return "invalid JPEG format: " + string(e) }
+func (e FormatError) Error() string { return "invalid JPEG format: " + string(e) }
 
 // An UnsupportedError reports that the input uses a valid but unimplemented JPEG feature.
 type UnsupportedError string
 
-func (e UnsupportedError) String() string { return "unsupported JPEG feature: " + string(e) }
+func (e UnsupportedError) Error() string { return "unsupported JPEG feature: " + string(e) }
 
 // Component specification, specified in section B.2.2.
 type component struct {
@@ -91,7 +90,7 @@ var unzig = [blockSize]int{
 // If the passed in io.Reader does not also have ReadByte, then Decode will introduce its own buffering.
 type Reader interface {
 	io.Reader
-	ReadByte() (c byte, err os.Error)
+	ReadByte() (c byte, err error)
 }
 
 type decoder struct {
@@ -109,7 +108,7 @@ type decoder struct {
 }
 
 // Reads and ignores the next n bytes.
-func (d *decoder) ignore(n int) os.Error {
+func (d *decoder) ignore(n int) error {
 	for n > 0 {
 		m := len(d.tmp)
 		if m > n {
@@ -125,7 +124,7 @@ func (d *decoder) ignore(n int) os.Error {
 }
 
 // Specified in section B.2.2.
-func (d *decoder) processSOF(n int) os.Error {
+func (d *decoder) processSOF(n int) error {
 	switch n {
 	case 6 + 3*nGrayComponent:
 		d.nComp = nGrayComponent
@@ -172,7 +171,7 @@ func (d *decoder) processSOF(n int) os.Error {
 }
 
 // Specified in section B.2.4.1.
-func (d *decoder) processDQT(n int) os.Error {
+func (d *decoder) processDQT(n int) error {
 	const qtLength = 1 + blockSize
 	for ; n >= qtLength; n -= qtLength {
 		_, err := io.ReadFull(d.r, d.tmp[0:qtLength])
@@ -229,7 +228,7 @@ func (d *decoder) makeImg(h0, v0, mxx, myy int) {
 }
 
 // Specified in section B.2.3.
-func (d *decoder) processSOS(n int) os.Error {
+func (d *decoder) processSOS(n int) error {
 	if d.nComp == 0 {
 		return FormatError("missing SOF marker")
 	}
@@ -362,7 +361,7 @@ func (d *decoder) processSOS(n int) os.Error {
 }
 
 // Specified in section B.2.4.4.
-func (d *decoder) processDRI(n int) os.Error {
+func (d *decoder) processDRI(n int) error {
 	if n != 2 {
 		return FormatError("DRI has wrong length")
 	}
@@ -375,7 +374,7 @@ func (d *decoder) processDRI(n int) os.Error {
 }
 
 // decode reads a JPEG image from r and returns it as an image.Image.
-func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, os.Error) {
+func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, error) {
 	if rr, ok := r.(Reader); ok {
 		d.r = rr
 	} else {
@@ -451,14 +450,14 @@ func (d *decoder) decode(r io.Reader, configOnly bool) (image.Image, os.Error) {
 }
 
 // Decode reads a JPEG image from r and returns it as an image.Image.
-func Decode(r io.Reader) (image.Image, os.Error) {
+func Decode(r io.Reader) (image.Image, error) {
 	var d decoder
 	return d.decode(r, false)
 }
 
 // DecodeConfig returns the color model and dimensions of a JPEG image without
 // decoding the entire image.
-func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+func DecodeConfig(r io.Reader) (image.Config, error) {
 	var d decoder
 	if _, err := d.decode(r, true); err != nil {
 		return image.Config{}, err
diff --git a/libgo/go/image/jpeg/writer.go b/libgo/go/image/jpeg/writer.go
index 2bb6df5..fab0bd0 100644
--- a/libgo/go/image/jpeg/writer.go
+++ b/libgo/go/image/jpeg/writer.go
@@ -6,10 +6,10 @@ package jpeg
 
 import (
 	"bufio"
+	"errors"
 	"image"
 	"image/ycbcr"
 	"io"
-	"os"
 )
 
 // min returns the minimum of two integers.
@@ -207,9 +207,9 @@ func init() {
 
 // writer is a buffered writer.
 type writer interface {
-	Flush() os.Error
-	Write([]byte) (int, os.Error)
-	WriteByte(byte) os.Error
+	Flush() error
+	Write([]byte) (int, error)
+	WriteByte(byte) error
 }
 
 // encoder encodes an image to the JPEG format.
@@ -217,7 +217,7 @@ type encoder struct {
 	// w is the writer to write to. err is the first error encountered during
 	// writing. All attempted writes after the first error become no-ops.
 	w   writer
-	err os.Error
+	err error
 	// buf is a scratch buffer.
 	buf [16]byte
 	// bits and nBits are accumulated bits to write to w.
@@ -487,10 +487,10 @@ type Options struct {
 
 // Encode writes the Image m to w in JPEG 4:2:0 baseline format with the given
 // options. Default parameters are used if a nil *Options is passed.
-func Encode(w io.Writer, m image.Image, o *Options) os.Error {
+func Encode(w io.Writer, m image.Image, o *Options) error {
 	b := m.Bounds()
 	if b.Dx() >= 1<<16 || b.Dy() >= 1<<16 {
-		return os.NewError("jpeg: image is too large to encode")
+		return errors.New("jpeg: image is too large to encode")
 	}
 	var e encoder
 	if ww, ok := w.(writer); ok {
diff --git a/libgo/go/image/jpeg/writer_test.go b/libgo/go/image/jpeg/writer_test.go
index 0378252..72cec93 100644
--- a/libgo/go/image/jpeg/writer_test.go
+++ b/libgo/go/image/jpeg/writer_test.go
@@ -36,7 +36,7 @@ func delta(u0, u1 uint32) int64 {
 	return d
 }
 
-func readPng(filename string) (image.Image, os.Error) {
+func readPng(filename string) (image.Image, error) {
 	f, err := os.Open(filename)
 	if err != nil {
 		return nil, err
diff --git a/libgo/go/image/png/reader.go b/libgo/go/image/png/reader.go
index 66f1916..7eb8cea 100644
--- a/libgo/go/image/png/reader.go
+++ b/libgo/go/image/png/reader.go
@@ -16,7 +16,6 @@ import (
 	"image"
 	"image/color"
 	"io"
-	"os"
 )
 
 // Color type, as per the PNG spec.
@@ -90,14 +89,14 @@ type decoder struct {
 // A FormatError reports that the input is not a valid PNG.
 type FormatError string
 
-func (e FormatError) String() string { return "png: invalid format: " + string(e) }
+func (e FormatError) Error() string { return "png: invalid format: " + string(e) }
 
 var chunkOrderError = FormatError("chunk out of order")
 
 // An UnsupportedError reports that the input uses a valid but unimplemented PNG feature.
 type UnsupportedError string
 
-func (e UnsupportedError) String() string { return "png: unsupported feature: " + string(e) }
+func (e UnsupportedError) Error() string { return "png: unsupported feature: " + string(e) }
 
 func abs(x int) int {
 	if x < 0 {
@@ -113,7 +112,7 @@ func min(a, b int) int {
 	return b
 }
 
-func (d *decoder) parseIHDR(length uint32) os.Error {
+func (d *decoder) parseIHDR(length uint32) error {
 	if length != 13 {
 		return FormatError("bad IHDR length")
 	}
@@ -189,7 +188,7 @@ func (d *decoder) parseIHDR(length uint32) os.Error {
 	return d.verifyChecksum()
 }
 
-func (d *decoder) parsePLTE(length uint32) os.Error {
+func (d *decoder) parsePLTE(length uint32) error {
 	np := int(length / 3) // The number of palette entries.
 	if length%3 != 0 || np <= 0 || np > 256 || np > 1<<uint(d.depth) {
 		return FormatError("bad PLTE length")
@@ -214,7 +213,7 @@ func (d *decoder) parsePLTE(length uint32) os.Error {
 	return d.verifyChecksum()
 }
 
-func (d *decoder) parsetRNS(length uint32) os.Error {
+func (d *decoder) parsetRNS(length uint32) error {
 	if length > 256 {
 		return FormatError("bad tRNS length")
 	}
@@ -263,7 +262,7 @@ func paeth(a, b, c uint8) uint8 {
 // immediately before the first Read call is that d.r is positioned between the
 // first IDAT and xxx, and the decoder state immediately after the last Read
 // call is that d.r is positioned between yy and crc1.
-func (d *decoder) Read(p []byte) (int, os.Error) {
+func (d *decoder) Read(p []byte) (int, error) {
 	if len(p) == 0 {
 		return 0, nil
 	}
@@ -294,7 +293,7 @@ func (d *decoder) Read(p []byte) (int, os.Error) {
 }
 
 // decode decodes the IDAT data into an image.
-func (d *decoder) decode() (image.Image, os.Error) {
+func (d *decoder) decode() (image.Image, error) {
 	r, err := zlib.NewReader(d)
 	if err != nil {
 		return nil, err
@@ -517,8 +516,8 @@ func (d *decoder) decode() (image.Image, os.Error) {
 
 	// Check for EOF, to verify the zlib checksum.
 	n, err := r.Read(pr[:1])
-	if err != os.EOF {
-		return nil, FormatError(err.String())
+	if err != io.EOF {
+		return nil, FormatError(err.Error())
 	}
 	if n != 0 || d.idatLength != 0 {
 		return nil, FormatError("too much pixel data")
@@ -527,7 +526,7 @@ func (d *decoder) decode() (image.Image, os.Error) {
 	return img, nil
 }
 
-func (d *decoder) parseIDAT(length uint32) (err os.Error) {
+func (d *decoder) parseIDAT(length uint32) (err error) {
 	d.idatLength = length
 	d.img, err = d.decode()
 	if err != nil {
@@ -536,14 +535,14 @@ func (d *decoder) parseIDAT(length uint32) (err os.Error) {
 	return d.verifyChecksum()
 }
 
-func (d *decoder) parseIEND(length uint32) os.Error {
+func (d *decoder) parseIEND(length uint32) error {
 	if length != 0 {
 		return FormatError("bad IEND length")
 	}
 	return d.verifyChecksum()
 }
 
-func (d *decoder) parseChunk() os.Error {
+func (d *decoder) parseChunk() error {
 	// Read the length and chunk type.
 	n, err := io.ReadFull(d.r, d.tmp[:8])
 	if err != nil {
@@ -598,7 +597,7 @@ func (d *decoder) parseChunk() os.Error {
 	return d.verifyChecksum()
 }
 
-func (d *decoder) verifyChecksum() os.Error {
+func (d *decoder) verifyChecksum() error {
 	if _, err := io.ReadFull(d.r, d.tmp[:4]); err != nil {
 		return err
 	}
@@ -608,7 +607,7 @@ func (d *decoder) verifyChecksum() os.Error {
 	return nil
 }
 
-func (d *decoder) checkHeader() os.Error {
+func (d *decoder) checkHeader() error {
 	_, err := io.ReadFull(d.r, d.tmp[:len(pngHeader)])
 	if err != nil {
 		return err
@@ -621,20 +620,20 @@ func (d *decoder) checkHeader() os.Error {
 
 // Decode reads a PNG image from r and returns it as an image.Image.
 // The type of Image returned depends on the PNG contents.
-func Decode(r io.Reader) (image.Image, os.Error) {
+func Decode(r io.Reader) (image.Image, error) {
 	d := &decoder{
 		r:   r,
 		crc: crc32.NewIEEE(),
 	}
 	if err := d.checkHeader(); err != nil {
-		if err == os.EOF {
+		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
 		}
 		return nil, err
 	}
 	for d.stage != dsSeenIEND {
 		if err := d.parseChunk(); err != nil {
-			if err == os.EOF {
+			if err == io.EOF {
 				err = io.ErrUnexpectedEOF
 			}
 			return nil, err
@@ -645,20 +644,20 @@ func Decode(r io.Reader) (image.Image, os.Error) {
 
 // DecodeConfig returns the color model and dimensions of a PNG image without
 // decoding the entire image.
-func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+func DecodeConfig(r io.Reader) (image.Config, error) {
 	d := &decoder{
 		r:   r,
 		crc: crc32.NewIEEE(),
 	}
 	if err := d.checkHeader(); err != nil {
-		if err == os.EOF {
+		if err == io.EOF {
 			err = io.ErrUnexpectedEOF
 		}
 		return image.Config{}, err
 	}
 	for {
 		if err := d.parseChunk(); err != nil {
-			if err == os.EOF {
+			if err == io.EOF {
 				err = io.ErrUnexpectedEOF
 			}
 			return image.Config{}, err
diff --git a/libgo/go/image/png/reader_test.go b/libgo/go/image/png/reader_test.go
index 48d0613..7eb1fc2 100644
--- a/libgo/go/image/png/reader_test.go
+++ b/libgo/go/image/png/reader_test.go
@@ -43,7 +43,7 @@ var filenamesShort = []string{
 	"basn6a16",
 }
 
-func readPNG(filename string) (image.Image, os.Error) {
+func readPNG(filename string) (image.Image, error) {
 	f, err := os.Open(filename)
 	if err != nil {
 		return nil, err
@@ -223,7 +223,7 @@ func TestReader(t *testing.T) {
 		for {
 			ps, perr := pb.ReadString('\n')
 			ss, serr := sb.ReadString('\n')
-			if perr == os.EOF && serr == os.EOF {
+			if perr == io.EOF && serr == io.EOF {
 				break
 			}
 			if perr != nil {
@@ -259,7 +259,7 @@ func TestReaderError(t *testing.T) {
 			t.Errorf("decoding %s: missing error", tt.file)
 			continue
 		}
-		if !strings.Contains(err.String(), tt.err) {
+		if !strings.Contains(err.Error(), tt.err) {
 			t.Errorf("decoding %s: %s, want %s", tt.file, err, tt.err)
 		}
 		if img != nil {
diff --git a/libgo/go/image/png/writer.go b/libgo/go/image/png/writer.go
index b6103c6..48089ff 100644
--- a/libgo/go/image/png/writer.go
+++ b/libgo/go/image/png/writer.go
@@ -11,7 +11,6 @@ import (
 	"image"
 	"image/color"
 	"io"
-	"os"
 	"strconv"
 )
 
@@ -19,7 +18,7 @@ type encoder struct {
 	w      io.Writer
 	m      image.Image
 	cb     int
-	err    os.Error
+	err    error
 	header [8]byte
 	footer [4]byte
 	tmp    [3 * 256]byte
@@ -161,7 +160,7 @@ func (e *encoder) maybeWritetRNS(p color.Palette) {
 //
 // This method should only be called from writeIDATs (via writeImage).
 // No other code should treat an encoder as an io.Writer.
-func (e *encoder) Write(b []byte) (int, os.Error) {
+func (e *encoder) Write(b []byte) (int, error) {
 	e.writeChunk(b, "IDAT")
 	if e.err != nil {
 		return 0, e.err
@@ -263,7 +262,7 @@ func filter(cr *[nFilter][]byte, pr []byte, bpp int) int {
 	return filter
 }
 
-func writeImage(w io.Writer, m image.Image, cb int) os.Error {
+func writeImage(w io.Writer, m image.Image, cb int) error {
 	zw, err := zlib.NewWriter(w)
 	if err != nil {
 		return err
@@ -424,7 +423,7 @@ func (e *encoder) writeIEND() { e.writeChunk(e.tmp[0:0], "IEND") }
 
 // Encode writes the Image m to w in PNG format. Any Image may be encoded, but
 // images that are not image.NRGBA might be encoded lossily.
-func Encode(w io.Writer, m image.Image) os.Error {
+func Encode(w io.Writer, m image.Image) error {
 	// Obviously, negative widths and heights are invalid. Furthermore, the PNG
 	// spec section 11.2.2 says that zero is invalid. Excessively large images are
 	// also rejected.
diff --git a/libgo/go/image/png/writer_test.go b/libgo/go/image/png/writer_test.go
index e517173..1757e14 100644
--- a/libgo/go/image/png/writer_test.go
+++ b/libgo/go/image/png/writer_test.go
@@ -10,11 +10,10 @@ import (
 	"image"
 	"image/color"
 	"io/ioutil"
-	"os"
 	"testing"
 )
 
-func diff(m0, m1 image.Image) os.Error {
+func diff(m0, m1 image.Image) error {
 	b0, b1 := m0.Bounds(), m1.Bounds()
 	if !b0.Size().Eq(b1.Size()) {
 		return fmt.Errorf("dimensions differ: %v vs %v", b0, b1)
@@ -35,7 +34,7 @@ func diff(m0, m1 image.Image) os.Error {
 	return nil
 }
 
-func encodeDecode(m image.Image) (image.Image, os.Error) {
+func encodeDecode(m image.Image) (image.Image, error) {
 	b := bytes.NewBuffer(nil)
 	err := Encode(b, m)
 	if err != nil {
diff --git a/libgo/go/image/tiff/buffer.go b/libgo/go/image/tiff/buffer.go
index 7c07142..ce35073 100644
--- a/libgo/go/image/tiff/buffer.go
+++ b/libgo/go/image/tiff/buffer.go
@@ -15,7 +15,7 @@ type buffer struct {
 	buf []byte
 }
 
-func (b *buffer) ReadAt(p []byte, off int64) (int, os.Error) {
+func (b *buffer) ReadAt(p []byte, off int64) (int, error) {
 	o := int(off)
 	end := o + len(p)
 	if int64(end) != off+int64(len(p)) {
diff --git a/libgo/go/image/tiff/buffer_test.go b/libgo/go/image/tiff/buffer_test.go
index 4f3e68e..e13afb3 100644
--- a/libgo/go/image/tiff/buffer_test.go
+++ b/libgo/go/image/tiff/buffer_test.go
@@ -5,7 +5,7 @@
 package tiff
 
 import (
-	"os"
+	"io"
 	"strings"
 	"testing"
 )
@@ -14,13 +14,13 @@ var readAtTests = []struct {
 	n   int
 	off int64
 	s   string
-	err os.Error
+	err error
 }{
 	{2, 0, "ab", nil},
 	{6, 0, "abcdef", nil},
 	{3, 3, "def", nil},
-	{3, 5, "f", os.EOF},
-	{3, 6, "", os.EOF},
+	{3, 5, "f", io.EOF},
+	{3, 6, "", io.EOF},
 }
 
 func TestReadAt(t *testing.T) {
diff --git a/libgo/go/image/tiff/compress.go b/libgo/go/image/tiff/compress.go
index e89aa6d..40c7fd8 100644
--- a/libgo/go/image/tiff/compress.go
+++ b/libgo/go/image/tiff/compress.go
@@ -7,7 +7,6 @@ package tiff
 import (
 	"bufio"
 	"io"
-	"os"
 )
 
 type byteReader interface {
@@ -20,7 +19,7 @@ type byteReader interface {
 //
 // The PackBits compression format is described in section 9 (p. 42)
 // of the TIFF spec.
-func unpackBits(r io.Reader) ([]byte, os.Error) {
+func unpackBits(r io.Reader) ([]byte, error) {
 	buf := make([]byte, 128)
 	dst := make([]byte, 0, 1024)
 	br, ok := r.(byteReader)
@@ -31,7 +30,7 @@ func unpackBits(r io.Reader) ([]byte, os.Error) {
 	for {
 		b, err := br.ReadByte()
 		if err != nil {
-			if err == os.EOF {
+			if err == io.EOF {
 				return dst, nil
 			}
 			return nil, err
diff --git a/libgo/go/image/tiff/reader.go b/libgo/go/image/tiff/reader.go
index c452f5d..00a51db 100644
--- a/libgo/go/image/tiff/reader.go
+++ b/libgo/go/image/tiff/reader.go
@@ -15,13 +15,12 @@ import (
 	"image/color"
 	"io"
 	"io/ioutil"
-	"os"
 )
 
 // A FormatError reports that the input is not a valid TIFF image.
 type FormatError string
 
-func (e FormatError) String() string {
+func (e FormatError) Error() string {
 	return "tiff: invalid format: " + string(e)
 }
 
@@ -29,14 +28,14 @@ func (e FormatError) String() string {
 // unimplemented feature.
 type UnsupportedError string
 
-func (e UnsupportedError) String() string {
+func (e UnsupportedError) Error() string {
 	return "tiff: unsupported feature: " + string(e)
 }
 
 // An InternalError reports that an internal error was encountered.
 type InternalError string
 
-func (e InternalError) String() string {
+func (e InternalError) Error() string {
 	return "tiff: internal error: " + string(e)
 }
 
@@ -66,7 +65,7 @@ func (d *decoder) firstVal(tag int) uint {
 
 // ifdUint decodes the IFD entry in p, which must be of the Byte, Short
 // or Long type, and returns the decoded uint values.
-func (d *decoder) ifdUint(p []byte) (u []uint, err os.Error) {
+func (d *decoder) ifdUint(p []byte) (u []uint, err error) {
 	var raw []byte
 	datatype := d.byteOrder.Uint16(p[2:4])
 	count := d.byteOrder.Uint32(p[4:8])
@@ -103,7 +102,7 @@ func (d *decoder) ifdUint(p []byte) (u []uint, err os.Error) {
 
 // parseIFD decides whether the the IFD entry in p is "interesting" and
 // stows away the data in the decoder.
-func (d *decoder) parseIFD(p []byte) os.Error {
+func (d *decoder) parseIFD(p []byte) error {
 	tag := d.byteOrder.Uint16(p[0:2])
 	switch tag {
 	case tBitsPerSample,
@@ -180,7 +179,7 @@ func (d *decoder) flushBits() {
 
 // decode decodes the raw data of an image.
 // It reads from d.buf and writes the strip with ymin <= y < ymax into dst.
-func (d *decoder) decode(dst image.Image, ymin, ymax int) os.Error {
+func (d *decoder) decode(dst image.Image, ymin, ymax int) error {
 	d.off = 0
 
 	// Apply horizontal predictor if necessary.
@@ -255,7 +254,7 @@ func (d *decoder) decode(dst image.Image, ymin, ymax int) os.Error {
 	return nil
 }
 
-func newDecoder(r io.Reader) (*decoder, os.Error) {
+func newDecoder(r io.Reader) (*decoder, error) {
 	d := &decoder{
 		r:        newReaderAt(r),
 		features: make(map[int][]uint),
@@ -350,7 +349,7 @@ func newDecoder(r io.Reader) (*decoder, os.Error) {
 
 // DecodeConfig returns the color model and dimensions of a TIFF image without
 // decoding the entire image.
-func DecodeConfig(r io.Reader) (image.Config, os.Error) {
+func DecodeConfig(r io.Reader) (image.Config, error) {
 	d, err := newDecoder(r)
 	if err != nil {
 		return image.Config{}, err
@@ -360,7 +359,7 @@ func DecodeConfig(r io.Reader) (image.Config, os.Error) {
 
 // Decode reads a TIFF image from r and returns it as an image.Image.
 // The type of Image returned depends on the contents of the TIFF.
-func Decode(r io.Reader) (img image.Image, err os.Error) {
+func Decode(r io.Reader) (img image.Image, err error) {
 	d, err := newDecoder(r)
 	if err != nil {
 		return
diff --git a/libgo/go/image/tiff/reader_test.go b/libgo/go/image/tiff/reader_test.go
index 86b7dc3..1a3d23b 100644
--- a/libgo/go/image/tiff/reader_test.go
+++ b/libgo/go/image/tiff/reader_test.go
@@ -13,7 +13,7 @@ import (
 )
 
 // Read makes *buffer implements io.Reader, so that we can pass one to Decode.
-func (*buffer) Read([]byte) (int, os.Error) {
+func (*buffer) Read([]byte) (int, error) {
 	panic("unimplemented")
 }