1 files changed, 310 insertions, 0 deletions
diff --git a/src/encoding/ascii85/ascii85.go b/src/encoding/ascii85/ascii85.go
new file mode 100644
index 000000000..4d7193873
--- /dev/null
+++ b/src/encoding/ascii85/ascii85.go
@@ -0,0 +1,310 @@
+// 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
+	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
+			}
+			if ndst == 0 && d.err == nil {
+				// Special case: input buffer is mostly filled with non-data bytes.
+				// Filter out such bytes to make room for more input.
+				off := 0
+				for i := 0; i < d.nbuf; i++ {
+					if d.buf[i] > ' ' {
+						d.buf[off] = d.buf[i]
+						off++
+					}
+				}
+				d.nbuf = off
+			}
+		}
+
+		// 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
+	}
+}