1 files changed, 284 insertions, 0 deletions
diff --git a/src/pkg/encoding/git85/git.go b/src/pkg/encoding/git85/git.go
new file mode 100644
index 000000000..2dcd4d877
--- /dev/null
+++ b/src/pkg/encoding/git85/git.go
@@ -0,0 +1,284 @@
+// 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 git85 implements the radix 85 data encoding
+// used in the GIT version control system.
+package git85
+
+import (
+	"bytes";
+	"io";
+	"os";
+	"strconv";
+)
+
+type CorruptInputError int64
+
+func (e CorruptInputError) String() string {
+	return "illegal git85 data at input byte" + strconv.Itoa64(int64(e));
+}
+
+const encode = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~"
+
+// The decodings are 1+ the actual value, so that the
+// default zero value can be used to mean "not valid".
+var decode = [256]uint8{
+	'0':	1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
+	'A':	11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
+		24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36,
+	'a':	37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
+		50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62,
+	'!':	63,
+	'#':	64, 65, 66, 67,
+	'(':	68, 69, 70, 71,
+	'-':	72,
+	';':	73,
+	'<':	74, 75, 76, 77,
+	'@':	78,
+	'^':	79, 80, 81,
+	'{':	82, 83, 84, 85
+}
+
+// Encode encodes src into EncodedLen(len(src))
+// bytes of dst.  As a convenience, it returns the number
+// of bytes written to dst, but this value is always EncodedLen(len(src)).
+// Encode implements the radix 85 encoding used in the
+// Git version control tool.
+//
+// The encoding splits src into chunks of at most 52 bytes
+// and encodes each chunk on its own line.
+func Encode(src, dst []byte) int {
+	ndst := 0;
+	for len(src) > 0 {
+		n := len(src);
+		if n > 52 {
+			n = 52;
+		}
+		if n <= 27 {
+			dst[ndst] = byte('A' + n - 1);
+		} else {
+			dst[ndst] = byte('a' + n - 26 - 1);
+		}
+		ndst++;
+		for i := 0; i < n; i += 4 {
+			var v uint32;
+			for j := 0; j < 4 && i+j < n; j++ {
+				v |= uint32(src[i+j]) << uint(24 - j*8);
+			}
+			for j := 4; j >= 0; j-- {
+				dst[ndst+j] = encode[v%85];
+				v /= 85;
+			}
+			ndst += 5;
+		}
+		dst[ndst] = '\n';
+		ndst++;
+		src = src[n:len(src)];
+	}
+	return ndst;
+}
+
+// EncodedLen returns the length of an encoding of n source bytes.
+func EncodedLen(n int) int {
+	if n == 0 {
+		return 0;
+	}
+	// 5 bytes per 4 bytes of input, rounded up.
+	// 2 extra bytes for each line of 52 src bytes, rounded up.
+	return (n+3)/4*5 + (n+51)/52*2;
+}
+
+var newline = []byte{'\n'}
+
+// Decode decodes src into at most MaxDecodedLen(len(src))
+// bytes, returning the actual number of bytes written to dst.
+//
+// If Decode encounters invalid input, it returns a CorruptInputError.
+//
+func Decode(src, dst []byte) (n int, err os.Error) {
+	ndst := 0;
+	nsrc := 0;
+	for nsrc < len(src) {
+		var l int;
+		switch ch := int(src[nsrc]); {
+		case 'A' <= ch && ch <= 'Z':
+			l = ch - 'A' + 1;
+		case 'a' <= ch && ch <= 'z':
+			l = ch - 'a' + 26 + 1;
+		default:
+			return ndst, CorruptInputError(nsrc);
+		}
+		if nsrc+1+l > len(src) {
+			return ndst, CorruptInputError(nsrc);
+		}
+		el := (l+3)/4*5;	// encoded len
+		if nsrc+1+el+1 > len(src) || src[nsrc+1+el] != '\n' {
+			return ndst, CorruptInputError(nsrc);
+		}
+		line := src[nsrc+1:nsrc+1+el];
+		for i := 0; i < el; i += 5 {
+			var v uint32;
+			for j := 0; j < 5; j++ {
+				ch := decode[line[i+j]];
+				if ch == 0 {
+					return ndst, CorruptInputError(nsrc+1+i+j);
+				}
+				v = v*85 + uint32(ch-1);
+			}
+			for j := 0; j < 4; j++ {
+				dst[ndst] = byte(v>>24);
+				v <<= 8;
+				ndst++;
+			}
+		}
+		// Last fragment may have run too far (but there was room in dst).
+		// Back up.
+		if l%4 != 0 {
+			ndst -= 4 - l%4;
+		}
+		nsrc += 1+el+1;
+	}
+	return ndst, nil;
+}
+
+func MaxDecodedLen(n int) int {
+	return n/5*4;
+}
+
+// NewEncoder returns a new Git base85 stream encoder.  Data written to
+// the returned writer will be encoded and then written to w.
+// The Git encoding operates on 52-byte blocks; when finished
+// writing, the caller must Close the returned encoder to flush any
+// partially written blocks.
+func NewEncoder(w io.Writer) io.WriteCloser {
+	return &encoder{w: w};
+}
+
+type encoder struct {
+	w io.Writer;
+	err os.Error;
+	buf [52]byte;
+	nbuf int;
+	out [1024]byte;
+	nout int;
+}
+
+func (e *encoder) Write(p []byte) (n int, err os.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 < 52; i++ {
+			e.buf[e.nbuf] = p[i];
+			e.nbuf++;
+		}
+		n += i;
+		p = p[i:len(p)];
+		if e.nbuf < 52 {
+			return;
+		}
+		nout := Encode(&e.buf, &e.out);
+		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) >= 52 {
+		nn := len(e.out)/(1+52/4*5+1) * 52;
+		if nn > len(p) {
+			nn = len(p)/52 * 52;
+		}
+		if nn > 0 {
+			nout := Encode(p[0:nn], &e.out);
+			if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
+				return n, e.err;
+			}
+		}
+		n += nn;
+		p = p[nn:len(p)];
+	}
+
+	// Trailing fringe.
+	for i := 0; i < len(p); i++ {
+		e.buf[i] = p[i];
+	}
+	e.nbuf = len(p);
+	n += len(p);
+	return;
+}
+
+func (e *encoder) Close() os.Error {
+	// If there's anything left in the buffer, flush it out
+	if e.err == nil && e.nbuf > 0 {
+		nout := Encode(e.buf[0:e.nbuf], &e.out);
+		e.nbuf = 0;
+		_, e.err = e.w.Write(e.out[0:nout]);
+	}
+	return e.err;
+}
+
+// NewDecoder returns a new Git base85 stream decoder.
+func NewDecoder(r io.Reader) io.Reader {
+	return &decoder{r: r};
+}
+
+type decoder struct {
+	r io.Reader;
+	err os.Error;
+	readErr os.Error;
+	buf [1024]byte;
+	nbuf int;
+	out []byte;
+	outbuf [1024]byte;
+	off int64;
+}
+
+func (d *decoder) Read(p []byte) (n int, err os.Error) {
+	if len(p) == 0 {
+		return 0, nil;
+	}
+
+	for {
+		// Copy leftover output from last decode.
+		if len(d.out) > 0 {
+			n = bytes.Copy(p, d.out);
+			d.out = d.out[n:len(d.out)];
+			return;
+		}
+
+		// 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 and decode more input.
+		var nn int;
+		nn, d.readErr = d.r.Read(d.buf[d.nbuf:len(d.buf)]);
+		d.nbuf += nn;
+
+		// Send complete lines to Decode.
+		nl := bytes.LastIndex(d.buf[0:d.nbuf], newline);
+		if nl < 0 {
+			continue;
+		}
+		nn, d.err = Decode(d.buf[0:nl+1], &d.outbuf);
+		if e, ok := d.err.(CorruptInputError); ok {
+			d.err = CorruptInputError(int64(e)+d.off);
+		}
+		d.out = d.outbuf[0:nn];
+		d.nbuf = bytes.Copy(&d.buf, d.buf[nl+1:d.nbuf]);
+		d.off += int64(nl+1);
+	}
+	panic("unreacahable");
+}
+