mirror of git://gcc.gnu.org/git/gcc.git
311 lines
6.9 KiB
Go
311 lines
6.9 KiB
Go
// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package ascii85 implements the ascii85 data encoding
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// as used in the btoa tool and Adobe's PostScript and PDF document formats.
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package ascii85
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import (
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"io"
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"strconv"
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)
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/*
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* Encoder
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*/
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// Encode encodes src into at most MaxEncodedLen(len(src))
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// bytes of dst, returning the actual number of bytes written.
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//
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// The encoding handles 4-byte chunks, using a special encoding
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// for the last fragment, so Encode is not appropriate for use on
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// individual blocks of a large data stream. Use NewEncoder() instead.
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//
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// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
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// Encode does not add these.
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func Encode(dst, src []byte) int {
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if len(src) == 0 {
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return 0
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}
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n := 0
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for len(src) > 0 {
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dst[0] = 0
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dst[1] = 0
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dst[2] = 0
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dst[3] = 0
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dst[4] = 0
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// Unpack 4 bytes into uint32 to repack into base 85 5-byte.
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var v uint32
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switch len(src) {
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default:
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v |= uint32(src[3])
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fallthrough
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case 3:
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v |= uint32(src[2]) << 8
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fallthrough
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case 2:
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v |= uint32(src[1]) << 16
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fallthrough
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case 1:
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v |= uint32(src[0]) << 24
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}
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// Special case: zero (!!!!!) shortens to z.
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if v == 0 && len(src) >= 4 {
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dst[0] = 'z'
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dst = dst[1:]
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src = src[4:]
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n++
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continue
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}
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// Otherwise, 5 base 85 digits starting at !.
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for i := 4; i >= 0; i-- {
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dst[i] = '!' + byte(v%85)
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v /= 85
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}
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// If src was short, discard the low destination bytes.
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m := 5
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if len(src) < 4 {
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m -= 4 - len(src)
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src = nil
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} else {
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src = src[4:]
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}
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dst = dst[m:]
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n += m
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}
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return n
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}
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// MaxEncodedLen returns the maximum length of an encoding of n source bytes.
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func MaxEncodedLen(n int) int { return (n + 3) / 4 * 5 }
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// NewEncoder returns a new ascii85 stream encoder. Data written to
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// the returned writer will be encoded and then written to w.
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// Ascii85 encodings operate in 32-bit blocks; when finished
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// writing, the caller must Close the returned encoder to flush any
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// trailing partial block.
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func NewEncoder(w io.Writer) io.WriteCloser { return &encoder{w: w} }
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type encoder struct {
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err error
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w io.Writer
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buf [4]byte // buffered data waiting to be encoded
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nbuf int // number of bytes in buf
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out [1024]byte // output buffer
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}
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func (e *encoder) Write(p []byte) (n int, err error) {
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if e.err != nil {
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return 0, e.err
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}
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// Leading fringe.
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if e.nbuf > 0 {
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var i int
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for i = 0; i < len(p) && e.nbuf < 4; i++ {
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e.buf[e.nbuf] = p[i]
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e.nbuf++
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}
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n += i
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p = p[i:]
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if e.nbuf < 4 {
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return
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}
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nout := Encode(e.out[0:], e.buf[0:])
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if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
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return n, e.err
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}
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e.nbuf = 0
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}
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// Large interior chunks.
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for len(p) >= 4 {
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nn := len(e.out) / 5 * 4
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if nn > len(p) {
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nn = len(p)
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}
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nn -= nn % 4
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if nn > 0 {
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nout := Encode(e.out[0:], p[0:nn])
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if _, e.err = e.w.Write(e.out[0:nout]); e.err != nil {
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return n, e.err
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}
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}
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n += nn
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p = p[nn:]
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}
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// Trailing fringe.
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for i := 0; i < len(p); i++ {
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e.buf[i] = p[i]
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}
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e.nbuf = len(p)
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n += len(p)
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return
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}
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// Close flushes any pending output from the encoder.
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// It is an error to call Write after calling Close.
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func (e *encoder) Close() error {
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// If there's anything left in the buffer, flush it out
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if e.err == nil && e.nbuf > 0 {
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nout := Encode(e.out[0:], e.buf[0:e.nbuf])
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e.nbuf = 0
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_, e.err = e.w.Write(e.out[0:nout])
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}
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return e.err
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}
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/*
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* Decoder
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*/
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type CorruptInputError int64
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func (e CorruptInputError) Error() string {
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return "illegal ascii85 data at input byte " + strconv.FormatInt(int64(e), 10)
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}
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// Decode decodes src into dst, returning both the number
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// of bytes written to dst and the number consumed from src.
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// If src contains invalid ascii85 data, Decode will return the
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// number of bytes successfully written and a CorruptInputError.
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// Decode ignores space and control characters in src.
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// Often, ascii85-encoded data is wrapped in <~ and ~> symbols.
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// Decode expects these to have been stripped by the caller.
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//
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// If flush is true, Decode assumes that src represents the
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// end of the input stream and processes it completely rather
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// than wait for the completion of another 32-bit block.
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//
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// NewDecoder wraps an io.Reader interface around Decode.
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//
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func Decode(dst, src []byte, flush bool) (ndst, nsrc int, err error) {
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var v uint32
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var nb int
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for i, b := range src {
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if len(dst)-ndst < 4 {
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return
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}
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switch {
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case b <= ' ':
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continue
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case b == 'z' && nb == 0:
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nb = 5
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v = 0
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case '!' <= b && b <= 'u':
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v = v*85 + uint32(b-'!')
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nb++
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default:
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return 0, 0, CorruptInputError(i)
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}
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if nb == 5 {
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nsrc = i + 1
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dst[ndst] = byte(v >> 24)
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dst[ndst+1] = byte(v >> 16)
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dst[ndst+2] = byte(v >> 8)
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dst[ndst+3] = byte(v)
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ndst += 4
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nb = 0
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v = 0
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}
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}
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if flush {
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nsrc = len(src)
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if nb > 0 {
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// The number of output bytes in the last fragment
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// is the number of leftover input bytes - 1:
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// the extra byte provides enough bits to cover
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// the inefficiency of the encoding for the block.
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if nb == 1 {
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return 0, 0, CorruptInputError(len(src))
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}
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for i := nb; i < 5; i++ {
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// The short encoding truncated the output value.
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// We have to assume the worst case values (digit 84)
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// in order to ensure that the top bits are correct.
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v = v*85 + 84
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}
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for i := 0; i < nb-1; i++ {
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dst[ndst] = byte(v >> 24)
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v <<= 8
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ndst++
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}
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}
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}
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return
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}
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// NewDecoder constructs a new ascii85 stream decoder.
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func NewDecoder(r io.Reader) io.Reader { return &decoder{r: r} }
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type decoder struct {
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err error
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readErr error
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r io.Reader
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buf [1024]byte // leftover input
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nbuf int
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out []byte // leftover decoded output
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outbuf [1024]byte
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}
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func (d *decoder) Read(p []byte) (n int, err error) {
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if len(p) == 0 {
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return 0, nil
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}
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if d.err != nil {
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return 0, d.err
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}
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for {
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// Copy leftover output from last decode.
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if len(d.out) > 0 {
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n = copy(p, d.out)
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d.out = d.out[n:]
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return
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}
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// Decode leftover input from last read.
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var nn, nsrc, ndst int
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if d.nbuf > 0 {
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ndst, nsrc, d.err = Decode(d.outbuf[0:], d.buf[0:d.nbuf], d.readErr != nil)
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if ndst > 0 {
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d.out = d.outbuf[0:ndst]
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d.nbuf = copy(d.buf[0:], d.buf[nsrc:d.nbuf])
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continue // copy out and return
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}
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if ndst == 0 && d.err == nil {
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// Special case: input buffer is mostly filled with non-data bytes.
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// Filter out such bytes to make room for more input.
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off := 0
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for i := 0; i < d.nbuf; i++ {
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if d.buf[i] > ' ' {
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d.buf[off] = d.buf[i]
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off++
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}
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}
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d.nbuf = off
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}
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}
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// Out of input, out of decoded output. Check errors.
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if d.err != nil {
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return 0, d.err
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}
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if d.readErr != nil {
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d.err = d.readErr
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return 0, d.err
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}
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// Read more data.
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nn, d.readErr = d.r.Read(d.buf[d.nbuf:])
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d.nbuf += nn
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}
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}
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