src/pkg/encoding/ascii85/ascii85.go - go - Git at Google

 // Copyright 2009 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 ascii85 implements the ascii85 data encoding
 // as used in the btoa tool and Adobe's PostScript and PDF document formats.
 package ascii85

 import (
 	"io"
 	"strconv"
 )

 /*
  * Encoder
  */

 // Encode encodes src into at most MaxEncodedLen(len(src))
 // bytes of dst, returning the actual number of bytes written.
 //
 // The encoding handles 4-byte chunks, using a special encoding
 // for the last fragment, so Encode is not appropriate for use on
 // individual blocks of a large data stream.  Use NewEncoder() instead.
 //
 // Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
 // Encode does not add these.
 func Encode(dst, src []byte) int {
 	if len(src) == 0 {
 		return 0
 	}

 	n := 0
 	for len(src) > 0 {
 		dst[0] = 0
 		dst[1] = 0
 		dst[2] = 0
 		dst[3] = 0
 		dst[4] = 0

 		// Unpack 4 bytes into uint32 to repack into base 85 5-byte.
 		var v uint32
 		switch len(src) {
 		default:
 			v |= uint32(src[3])
 			fallthrough
 		case 3:
 			v |= uint32(src[2]) << 8
 			fallthrough
 		case 2:
 			v |= uint32(src[1]) << 16
 			fallthrough
 		case 1:
 			v |= uint32(src[0]) << 24
 		}

 		// Special case: zero (!!!!!) shortens to z.
 		if v == 0 && len(src) >= 4 {
 			dst[0] = 'z'
 			dst = dst[1:]
 			src = src[4:]
 			n++
 			continue
 		}

 		// Otherwise, 5 base 85 digits starting at !.
 		for i := 4; i >= 0; i-- {
 			dst[i] = '!' + byte(v%85)
 			v /= 85
 		}

 		// If src was short, discard the low destination bytes.
 		m := 5
 		if len(src) < 4 {
 			m -= 4 - len(src)
 			src = nil
 		} else {
 			src = src[4:]
 		}
 		dst = dst[m:]
 		n += m
 	}
 	return n
 }

 // MaxEncodedLen returns the maximum length of an encoding of n source bytes.
 func MaxEncodedLen(n int) int { return (n + 3) / 4 * 5 }

 // NewEncoder returns a new ascii85 stream encoder.  Data written to
 // the returned writer will be encoded and then written to w.
 // Ascii85 encodings operate in 32-bit blocks; when finished
 // writing, the caller must Close the returned encoder to flush any
 // trailing partial block.
 func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} }

 type encoder struct {
 	err  error
 	w    io.Writer
 	buf  [4]byte    // buffered data waiting to be encoded
 	nbuf int        // number of bytes in buf
 	out  [1024]byte // output buffer
 }

 func (e *encoder) Write(p []byte) (n int, err error) {
 	if e.err != nil {
 		return 0, e.err
 	}

 	// Leading fringe.
 	if e.nbuf > 0 {
 		var i int
 		for i = 0; i < len(p) && e.nbuf < 4; i++ {
 			e.buf[e.nbuf] = p[i]
 			e.nbuf++
 		}
 		n += i
 		p = p[i:]
 		if e.nbuf < 4 {
 			return
 		}
 		nout := Encode(e.out[0:], e.buf[0:])
 		if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
 			return n, e.err
 		}
 		e.nbuf = 0
 	}

 	// Large interior chunks.
 	for len(p) >= 4 {
 		nn := len(e.out) / 5 * 4
 		if nn > len(p) {
 			nn = len(p)
 		}
 		nn -= nn % 4
 		if nn > 0 {
 			nout := Encode(e.out[0:], p[0:nn])
 			if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
 				return n, e.err
 			}
 		}
 		n += nn
 		p = p[nn:]
 	}

 	// Trailing fringe.
 	for i := 0; i < len(p); i++ {
 		e.buf[i] = p[i]
 	}
 	e.nbuf = len(p)
 	n += len(p)
 	return
 }

 // Close flushes any pending output from the encoder.
 // It is an error to call Write after calling Close.
 func (e *encoder) Close() error {
 	// If there's anything left in the buffer, flush it out
 	if e.err == nil && e.nbuf > 0 {
 		nout := Encode(e.out[0:], e.buf[0:e.nbuf])
 		e.nbuf = 0
 		_, e.err = e.w.Write(e.out[0:nout])
 	}
 	return e.err
 }

 /*
  * Decoder
  */

 type CorruptInputError int64

 func (e CorruptInputError) Error() string {
 	return "illegal ascii85 data at input byte " + strconv.FormatInt(int64(e), 10)
 }

 // Decode decodes src into dst, returning both the number
 // of bytes written to dst and the number consumed from src.
 // If src contains invalid ascii85 data, Decode will return the
 // number of bytes successfully written and a CorruptInputError.
 // Decode ignores space and control characters in src.
 // Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
 // Decode expects these to have been stripped by the caller.
 //
 // If flush is true, Decode assumes that src represents the
 // end of the input stream and processes it completely rather
 // than wait for the completion of another 32-bit block.
 //
 // NewDecoder wraps an io.Reader interface around Decode.
 //
 func Decode(dst, src []byte, flush bool) (ndst, nsrc int, err error) {
 	var v uint32
 	var nb int
 	for i, b := range src {
 		if len(dst)-ndst < 4 {
 			return
 		}
 		switch {
 		case b <= ' ':
 			continue
 		case b == 'z' && nb == 0:
 			nb = 5
 			v = 0
 		case '!' <= b && b <= 'u':
 			v = v*85 + uint32(b-'!')
 			nb++
 		default:
 			return 0, 0, CorruptInputError(i)
 		}
 		if nb == 5 {
 			nsrc = i + 1
 			dst[ndst] = byte(v >> 24)
 			dst[ndst+1] = byte(v >> 16)
 			dst[ndst+2] = byte(v >> 8)
 			dst[ndst+3] = byte(v)
 			ndst += 4
 			nb = 0
 			v = 0
 		}
 	}
 	if flush {
 		nsrc = len(src)
 		if nb > 0 {
 			// The number of output bytes in the last fragment
 			// is the number of leftover input bytes - 1:
 			// the extra byte provides enough bits to cover
 			// the inefficiency of the encoding for the block.
 			if nb == 1 {
 				return 0, 0, CorruptInputError(len(src))
 			}
 			for i := nb; i < 5; i++ {
 				// The short encoding truncated the output value.
 				// We have to assume the worst case values (digit 84)
 				// in order to ensure that the top bits are correct.
 				v = v*85 + 84
 			}
 			for i := 0; i < nb-1; i++ {
 				dst[ndst] = byte(v >> 24)
 				v <<= 8
 				ndst++
 			}
 		}
 	}
 	return
 }

 // NewDecoder constructs a new ascii85 stream decoder.
 func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} }

 type decoder struct {
 	err     error
 	readErr error
 	r       io.Reader
 	end     bool       // saw end of message
 	buf     [1024]byte // leftover input
 	nbuf    int
 	out     []byte // leftover decoded output
 	outbuf  [1024]byte
 }

 func (d *decoder) Read(p []byte) (n int, err error) {
 	if len(p) == 0 {
 		return 0, nil
 	}
 	if d.err != nil {
 		return 0, d.err
 	}

 	for {
 		// Copy leftover output from last decode.
 		if len(d.out) > 0 {
 			n = copy(p, d.out)
 			d.out = d.out[n:]
 			return
 		}

 		// Decode leftover input from last read.
 		var nn, nsrc, ndst int
 		if d.nbuf > 0 {
 			ndst, nsrc, d.err = Decode(d.outbuf[0:], d.buf[0:d.nbuf], d.readErr != nil)
 			if ndst > 0 {
 				d.out = d.outbuf[0:ndst]
 				d.nbuf = copy(d.buf[0:], d.buf[nsrc:d.nbuf])
 				continue // copy out and return
 			}
 		}

 		// Out of input, out of decoded output.  Check errors.
 		if d.err != nil {
 			return 0, d.err
 		}
 		if d.readErr != nil {
 			d.err = d.readErr
 			return 0, d.err
 		}

 		// Read more data.
 		nn, d.readErr = d.r.Read(d.buf[d.nbuf:])
 		d.nbuf += nn
 	}
 	panic("unreachable")
 }
	// Copyright 2009 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 ascii85 implements the ascii85 data encoding
	// as used in the btoa tool and Adobe's PostScript and PDF document formats.
	package ascii85

	import (
	"io"
	"strconv"
	)

	/*
	* Encoder
	*/

	// Encode encodes src into at most MaxEncodedLen(len(src))
	// bytes of dst, returning the actual number of bytes written.
	//
	// The encoding handles 4-byte chunks, using a special encoding
	// for the last fragment, so Encode is not appropriate for use on
	// individual blocks of a large data stream. Use NewEncoder() instead.
	//
	// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
	// Encode does not add these.
	func Encode(dst, src []byte) int {
	if len(src) == 0 {
	return 0
	}

	n := 0
	for len(src) > 0 {
	dst[0] = 0
	dst[1] = 0
	dst[2] = 0
	dst[3] = 0
	dst[4] = 0

	// Unpack 4 bytes into uint32 to repack into base 85 5-byte.
	var v uint32
	switch len(src) {
	default:
	v \|= uint32(src[3])
	fallthrough
	case 3:
	v \|= uint32(src[2]) << 8
	fallthrough
	case 2:
	v \|= uint32(src[1]) << 16
	fallthrough
	case 1:
	v \|= uint32(src[0]) << 24
	}

	// Special case: zero (!!!!!) shortens to z.
	if v == 0 && len(src) >= 4 {
	dst[0] = 'z'
	dst = dst[1:]
	src = src[4:]
	n++
	continue
	}

	// Otherwise, 5 base 85 digits starting at !.
	for i := 4; i >= 0; i-- {
	dst[i] = '!' + byte(v%85)
	v /= 85
	}

	// If src was short, discard the low destination bytes.
	m := 5
	if len(src) < 4 {
	m -= 4 - len(src)
	src = nil
	} else {
	src = src[4:]
	}
	dst = dst[m:]
	n += m
	}
	return n
	}

	// MaxEncodedLen returns the maximum length of an encoding of n source bytes.
	func MaxEncodedLen(n int) int { return (n + 3) / 4 * 5 }

	// NewEncoder returns a new ascii85 stream encoder. Data written to
	// the returned writer will be encoded and then written to w.
	// Ascii85 encodings operate in 32-bit blocks; when finished
	// writing, the caller must Close the returned encoder to flush any
	// trailing partial block.
	func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} }

	type encoder struct {
	err error
	w io.Writer
	buf [4]byte // buffered data waiting to be encoded
	nbuf int // number of bytes in buf
	out [1024]byte // output buffer
	}

	func (e *encoder) Write(p []byte) (n int, err error) {
	if e.err != nil {
	return 0, e.err
	}

	// Leading fringe.
	if e.nbuf > 0 {
	var i int
	for i = 0; i < len(p) && e.nbuf < 4; i++ {
	e.buf[e.nbuf] = p[i]
	e.nbuf++
	}
	n += i
	p = p[i:]
	if e.nbuf < 4 {
	return
	}
	nout := Encode(e.out[0:], e.buf[0:])
	if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
	return n, e.err
	}
	e.nbuf = 0
	}

	// Large interior chunks.
	for len(p) >= 4 {
	nn := len(e.out) / 5 * 4
	if nn > len(p) {
	nn = len(p)
	}
	nn -= nn % 4
	if nn > 0 {
	nout := Encode(e.out[0:], p[0:nn])
	if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
	return n, e.err
	}
	}
	n += nn
	p = p[nn:]
	}

	// Trailing fringe.
	for i := 0; i < len(p); i++ {
	e.buf[i] = p[i]
	}
	e.nbuf = len(p)
	n += len(p)
	return
	}

	// Close flushes any pending output from the encoder.
	// It is an error to call Write after calling Close.
	func (e *encoder) Close() error {
	// If there's anything left in the buffer, flush it out
	if e.err == nil && e.nbuf > 0 {
	nout := Encode(e.out[0:], e.buf[0:e.nbuf])
	e.nbuf = 0
	_, e.err = e.w.Write(e.out[0:nout])
	}
	return e.err
	}

	/*
	* Decoder
	*/

	type CorruptInputError int64

	func (e CorruptInputError) Error() string {
	return "illegal ascii85 data at input byte " + strconv.FormatInt(int64(e), 10)
	}

	// Decode decodes src into dst, returning both the number
	// of bytes written to dst and the number consumed from src.
	// If src contains invalid ascii85 data, Decode will return the
	// number of bytes successfully written and a CorruptInputError.
	// Decode ignores space and control characters in src.
	// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
	// Decode expects these to have been stripped by the caller.
	//
	// If flush is true, Decode assumes that src represents the
	// end of the input stream and processes it completely rather
	// than wait for the completion of another 32-bit block.
	//
	// NewDecoder wraps an io.Reader interface around Decode.
	//
	func Decode(dst, src []byte, flush bool) (ndst, nsrc int, err error) {
	var v uint32
	var nb int
	for i, b := range src {
	if len(dst)-ndst < 4 {
	return
	}
	switch {
	case b <= ' ':
	continue
	case b == 'z' && nb == 0:
	nb = 5
	v = 0
	case '!' <= b && b <= 'u':
	v = v*85 + uint32(b-'!')
	nb++
	default:
	return 0, 0, CorruptInputError(i)
	}
	if nb == 5 {
	nsrc = i + 1
	dst[ndst] = byte(v >> 24)
	dst[ndst+1] = byte(v >> 16)
	dst[ndst+2] = byte(v >> 8)
	dst[ndst+3] = byte(v)
	ndst += 4
	nb = 0
	v = 0
	}
	}
	if flush {
	nsrc = len(src)
	if nb > 0 {
	// The number of output bytes in the last fragment
	// is the number of leftover input bytes - 1:
	// the extra byte provides enough bits to cover
	// the inefficiency of the encoding for the block.
	if nb == 1 {
	return 0, 0, CorruptInputError(len(src))
	}
	for i := nb; i < 5; i++ {
	// The short encoding truncated the output value.
	// We have to assume the worst case values (digit 84)
	// in order to ensure that the top bits are correct.
	v = v*85 + 84
	}
	for i := 0; i < nb-1; i++ {
	dst[ndst] = byte(v >> 24)
	v <<= 8
	ndst++
	}
	}
	}
	return
	}

	// NewDecoder constructs a new ascii85 stream decoder.
	func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} }

	type decoder struct {
	err error
	readErr error
	r io.Reader
	end bool // saw end of message
	buf [1024]byte // leftover input
	nbuf int
	out []byte // leftover decoded output
	outbuf [1024]byte
	}

	func (d *decoder) Read(p []byte) (n int, err error) {
	if len(p) == 0 {
	return 0, nil
	}
	if d.err != nil {
	return 0, d.err
	}

	for {
	// Copy leftover output from last decode.
	if len(d.out) > 0 {
	n = copy(p, d.out)
	d.out = d.out[n:]
	return
	}

	// Decode leftover input from last read.
	var nn, nsrc, ndst int
	if d.nbuf > 0 {
	ndst, nsrc, d.err = Decode(d.outbuf[0:], d.buf[0:d.nbuf], d.readErr != nil)
	if ndst > 0 {
	d.out = d.outbuf[0:ndst]
	d.nbuf = copy(d.buf[0:], d.buf[nsrc:d.nbuf])
	continue // copy out and return
	}
	}

	// Out of input, out of decoded output. Check errors.
	if d.err != nil {
	return 0, d.err
	}
	if d.readErr != nil {
	d.err = d.readErr
	return 0, d.err
	}

	// Read more data.
	nn, d.readErr = d.r.Read(d.buf[d.nbuf:])
	d.nbuf += nn
	}
	panic("unreachable")
	}