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989489096e
This commit implements a massive refactor of the repository, and moves the build system over to use Mage (magefile.org) which should allow seamless building across multiple platforms.
111 lines
3.0 KiB
Go
111 lines
3.0 KiB
Go
// Copyright 2015, Joe Tsai. 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.md file.
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// Package bzip2 implements the BZip2 compressed data format.
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//
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// Canonical C implementation:
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// http://bzip.org
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//
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// Unofficial format specification:
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// https://github.com/dsnet/compress/blob/master/doc/bzip2-format.pdf
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package bzip2
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import (
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"fmt"
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"hash/crc32"
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"github.com/dsnet/compress/internal"
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"github.com/dsnet/compress/internal/errors"
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)
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// There does not exist a formal specification of the BZip2 format. As such,
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// much of this work is derived by either reverse engineering the original C
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// source code or using secondary sources.
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//
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// Significant amounts of fuzz testing is done to ensure that outputs from
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// this package is properly decoded by the C library. Furthermore, we test that
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// both this package and the C library agree about what inputs are invalid.
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//
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// Compression stack:
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// Run-length encoding 1 (RLE1)
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// Burrows-Wheeler transform (BWT)
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// Move-to-front transform (MTF)
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// Run-length encoding 2 (RLE2)
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// Prefix encoding (PE)
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//
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// References:
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// http://bzip.org/
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// https://en.wikipedia.org/wiki/Bzip2
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// https://code.google.com/p/jbzip2/
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const (
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BestSpeed = 1
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BestCompression = 9
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DefaultCompression = 6
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)
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const (
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hdrMagic = 0x425a // Hex of "BZ"
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blkMagic = 0x314159265359 // BCD of PI
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endMagic = 0x177245385090 // BCD of sqrt(PI)
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blockSize = 100000
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)
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func errorf(c int, f string, a ...interface{}) error {
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return errors.Error{Code: c, Pkg: "bzip2", Msg: fmt.Sprintf(f, a...)}
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}
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func panicf(c int, f string, a ...interface{}) {
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errors.Panic(errorf(c, f, a...))
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}
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// errWrap converts a lower-level errors.Error to be one from this package.
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// The replaceCode passed in will be used to replace the code for any errors
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// with the errors.Invalid code.
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//
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// For the Reader, set this to errors.Corrupted.
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// For the Writer, set this to errors.Internal.
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func errWrap(err error, replaceCode int) error {
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if cerr, ok := err.(errors.Error); ok {
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if errors.IsInvalid(cerr) {
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cerr.Code = replaceCode
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}
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err = errorf(cerr.Code, "%s", cerr.Msg)
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}
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return err
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}
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var errClosed = errorf(errors.Closed, "")
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// crc computes the CRC-32 used by BZip2.
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//
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// The CRC-32 computation in bzip2 treats bytes as having bits in big-endian
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// order. That is, the MSB is read before the LSB. Thus, we can use the
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// standard library version of CRC-32 IEEE with some minor adjustments.
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//
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// The byte array is used as an intermediate buffer to swap the bits of every
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// byte of the input.
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type crc struct {
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val uint32
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buf [256]byte
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}
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// update computes the CRC-32 of appending buf to c.
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func (c *crc) update(buf []byte) {
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cval := internal.ReverseUint32(c.val)
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for len(buf) > 0 {
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n := len(buf)
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if n > len(c.buf) {
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n = len(c.buf)
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}
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for i, b := range buf[:n] {
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c.buf[i] = internal.ReverseLUT[b]
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}
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cval = crc32.Update(cval, crc32.IEEETable, c.buf[:n])
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buf = buf[n:]
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}
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c.val = internal.ReverseUint32(cval)
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}
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