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path: root/src/pkg/compress/bzip2/bzip2.go
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Diffstat (limited to 'src/pkg/compress/bzip2/bzip2.go')
-rw-r--r--src/pkg/compress/bzip2/bzip2.go484
1 files changed, 0 insertions, 484 deletions
diff --git a/src/pkg/compress/bzip2/bzip2.go b/src/pkg/compress/bzip2/bzip2.go
deleted file mode 100644
index 82e30c7c9..000000000
--- a/src/pkg/compress/bzip2/bzip2.go
+++ /dev/null
@@ -1,484 +0,0 @@
-// Copyright 2011 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 bzip2 implements bzip2 decompression.
-package bzip2
-
-import "io"
-
-// There's no RFC for bzip2. I used the Wikipedia page for reference and a lot
-// of guessing: http://en.wikipedia.org/wiki/Bzip2
-// The source code to pyflate was useful for debugging:
-// http://www.paul.sladen.org/projects/pyflate
-
-// A StructuralError is returned when the bzip2 data is found to be
-// syntactically invalid.
-type StructuralError string
-
-func (s StructuralError) Error() string {
- return "bzip2 data invalid: " + string(s)
-}
-
-// A reader decompresses bzip2 compressed data.
-type reader struct {
- br bitReader
- fileCRC uint32
- blockCRC uint32
- wantBlockCRC uint32
- setupDone bool // true if we have parsed the bzip2 header.
- blockSize int // blockSize in bytes, i.e. 900 * 1024.
- eof bool
- buf []byte // stores Burrows-Wheeler transformed data.
- c [256]uint // the `C' array for the inverse BWT.
- tt []uint32 // mirrors the `tt' array in the bzip2 source and contains the P array in the upper 24 bits.
- tPos uint32 // Index of the next output byte in tt.
-
- preRLE []uint32 // contains the RLE data still to be processed.
- preRLEUsed int // number of entries of preRLE used.
- lastByte int // the last byte value seen.
- byteRepeats uint // the number of repeats of lastByte seen.
- repeats uint // the number of copies of lastByte to output.
-}
-
-// NewReader returns an io.Reader which decompresses bzip2 data from r.
-func NewReader(r io.Reader) io.Reader {
- bz2 := new(reader)
- bz2.br = newBitReader(r)
- return bz2
-}
-
-const bzip2FileMagic = 0x425a // "BZ"
-const bzip2BlockMagic = 0x314159265359
-const bzip2FinalMagic = 0x177245385090
-
-// setup parses the bzip2 header.
-func (bz2 *reader) setup(needMagic bool) error {
- br := &bz2.br
-
- if needMagic {
- magic := br.ReadBits(16)
- if magic != bzip2FileMagic {
- return StructuralError("bad magic value")
- }
- }
-
- t := br.ReadBits(8)
- if t != 'h' {
- return StructuralError("non-Huffman entropy encoding")
- }
-
- level := br.ReadBits(8)
- if level < '1' || level > '9' {
- return StructuralError("invalid compression level")
- }
-
- bz2.fileCRC = 0
- bz2.blockSize = 100 * 1024 * (int(level) - '0')
- if bz2.blockSize > len(bz2.tt) {
- bz2.tt = make([]uint32, bz2.blockSize)
- }
- return nil
-}
-
-func (bz2 *reader) Read(buf []byte) (n int, err error) {
- if bz2.eof {
- return 0, io.EOF
- }
-
- if !bz2.setupDone {
- err = bz2.setup(true)
- brErr := bz2.br.Err()
- if brErr != nil {
- err = brErr
- }
- if err != nil {
- return 0, err
- }
- bz2.setupDone = true
- }
-
- n, err = bz2.read(buf)
- brErr := bz2.br.Err()
- if brErr != nil {
- err = brErr
- }
- return
-}
-
-func (bz2 *reader) readFromBlock(buf []byte) int {
- // bzip2 is a block based compressor, except that it has a run-length
- // preprocessing step. The block based nature means that we can
- // preallocate fixed-size buffers and reuse them. However, the RLE
- // preprocessing would require allocating huge buffers to store the
- // maximum expansion. Thus we process blocks all at once, except for
- // the RLE which we decompress as required.
- n := 0
- for (bz2.repeats > 0 || bz2.preRLEUsed < len(bz2.preRLE)) && n < len(buf) {
- // We have RLE data pending.
-
- // The run-length encoding works like this:
- // Any sequence of four equal bytes is followed by a length
- // byte which contains the number of repeats of that byte to
- // include. (The number of repeats can be zero.) Because we are
- // decompressing on-demand our state is kept in the reader
- // object.
-
- if bz2.repeats > 0 {
- buf[n] = byte(bz2.lastByte)
- n++
- bz2.repeats--
- if bz2.repeats == 0 {
- bz2.lastByte = -1
- }
- continue
- }
-
- bz2.tPos = bz2.preRLE[bz2.tPos]
- b := byte(bz2.tPos)
- bz2.tPos >>= 8
- bz2.preRLEUsed++
-
- if bz2.byteRepeats == 3 {
- bz2.repeats = uint(b)
- bz2.byteRepeats = 0
- continue
- }
-
- if bz2.lastByte == int(b) {
- bz2.byteRepeats++
- } else {
- bz2.byteRepeats = 0
- }
- bz2.lastByte = int(b)
-
- buf[n] = b
- n++
- }
-
- return n
-}
-
-func (bz2 *reader) read(buf []byte) (int, error) {
- for {
- n := bz2.readFromBlock(buf)
- if n > 0 {
- bz2.blockCRC = updateCRC(bz2.blockCRC, buf[:n])
- return n, nil
- }
-
- // End of block. Check CRC.
- if bz2.blockCRC != bz2.wantBlockCRC {
- bz2.br.err = StructuralError("block checksum mismatch")
- return 0, bz2.br.err
- }
-
- // Find next block.
- br := &bz2.br
- switch br.ReadBits64(48) {
- default:
- return 0, StructuralError("bad magic value found")
-
- case bzip2BlockMagic:
- // Start of block.
- err := bz2.readBlock()
- if err != nil {
- return 0, err
- }
-
- case bzip2FinalMagic:
- // Check end-of-file CRC.
- wantFileCRC := uint32(br.ReadBits64(32))
- if br.err != nil {
- return 0, br.err
- }
- if bz2.fileCRC != wantFileCRC {
- br.err = StructuralError("file checksum mismatch")
- return 0, br.err
- }
-
- // Skip ahead to byte boundary.
- // Is there a file concatenated to this one?
- // It would start with BZ.
- if br.bits%8 != 0 {
- br.ReadBits(br.bits % 8)
- }
- b, err := br.r.ReadByte()
- if err == io.EOF {
- br.err = io.EOF
- bz2.eof = true
- return 0, io.EOF
- }
- if err != nil {
- br.err = err
- return 0, err
- }
- z, err := br.r.ReadByte()
- if err != nil {
- if err == io.EOF {
- err = io.ErrUnexpectedEOF
- }
- br.err = err
- return 0, err
- }
- if b != 'B' || z != 'Z' {
- return 0, StructuralError("bad magic value in continuation file")
- }
- if err := bz2.setup(false); err != nil {
- return 0, err
- }
- }
- }
-}
-
-// readBlock reads a bzip2 block. The magic number should already have been consumed.
-func (bz2 *reader) readBlock() (err error) {
- br := &bz2.br
- bz2.wantBlockCRC = uint32(br.ReadBits64(32)) // skip checksum. TODO: check it if we can figure out what it is.
- bz2.blockCRC = 0
- bz2.fileCRC = (bz2.fileCRC<<1 | bz2.fileCRC>>31) ^ bz2.wantBlockCRC
- randomized := br.ReadBits(1)
- if randomized != 0 {
- return StructuralError("deprecated randomized files")
- }
- origPtr := uint(br.ReadBits(24))
-
- // If not every byte value is used in the block (i.e., it's text) then
- // the symbol set is reduced. The symbols used are stored as a
- // two-level, 16x16 bitmap.
- symbolRangeUsedBitmap := br.ReadBits(16)
- symbolPresent := make([]bool, 256)
- numSymbols := 0
- for symRange := uint(0); symRange < 16; symRange++ {
- if symbolRangeUsedBitmap&(1<<(15-symRange)) != 0 {
- bits := br.ReadBits(16)
- for symbol := uint(0); symbol < 16; symbol++ {
- if bits&(1<<(15-symbol)) != 0 {
- symbolPresent[16*symRange+symbol] = true
- numSymbols++
- }
- }
- }
- }
-
- // A block uses between two and six different Huffman trees.
- numHuffmanTrees := br.ReadBits(3)
- if numHuffmanTrees < 2 || numHuffmanTrees > 6 {
- return StructuralError("invalid number of Huffman trees")
- }
-
- // The Huffman tree can switch every 50 symbols so there's a list of
- // tree indexes telling us which tree to use for each 50 symbol block.
- numSelectors := br.ReadBits(15)
- treeIndexes := make([]uint8, numSelectors)
-
- // The tree indexes are move-to-front transformed and stored as unary
- // numbers.
- mtfTreeDecoder := newMTFDecoderWithRange(numHuffmanTrees)
- for i := range treeIndexes {
- c := 0
- for {
- inc := br.ReadBits(1)
- if inc == 0 {
- break
- }
- c++
- }
- if c >= numHuffmanTrees {
- return StructuralError("tree index too large")
- }
- treeIndexes[i] = uint8(mtfTreeDecoder.Decode(c))
- }
-
- // The list of symbols for the move-to-front transform is taken from
- // the previously decoded symbol bitmap.
- symbols := make([]byte, numSymbols)
- nextSymbol := 0
- for i := 0; i < 256; i++ {
- if symbolPresent[i] {
- symbols[nextSymbol] = byte(i)
- nextSymbol++
- }
- }
- mtf := newMTFDecoder(symbols)
-
- numSymbols += 2 // to account for RUNA and RUNB symbols
- huffmanTrees := make([]huffmanTree, numHuffmanTrees)
-
- // Now we decode the arrays of code-lengths for each tree.
- lengths := make([]uint8, numSymbols)
- for i := 0; i < numHuffmanTrees; i++ {
- // The code lengths are delta encoded from a 5-bit base value.
- length := br.ReadBits(5)
- for j := 0; j < numSymbols; j++ {
- for {
- if !br.ReadBit() {
- break
- }
- if br.ReadBit() {
- length--
- } else {
- length++
- }
- }
- if length < 0 || length > 20 {
- return StructuralError("Huffman length out of range")
- }
- lengths[j] = uint8(length)
- }
- huffmanTrees[i], err = newHuffmanTree(lengths)
- if err != nil {
- return err
- }
- }
-
- selectorIndex := 1 // the next tree index to use
- currentHuffmanTree := huffmanTrees[treeIndexes[0]]
- bufIndex := 0 // indexes bz2.buf, the output buffer.
- // The output of the move-to-front transform is run-length encoded and
- // we merge the decoding into the Huffman parsing loop. These two
- // variables accumulate the repeat count. See the Wikipedia page for
- // details.
- repeat := 0
- repeat_power := 0
-
- // The `C' array (used by the inverse BWT) needs to be zero initialized.
- for i := range bz2.c {
- bz2.c[i] = 0
- }
-
- decoded := 0 // counts the number of symbols decoded by the current tree.
- for {
- if decoded == 50 {
- currentHuffmanTree = huffmanTrees[treeIndexes[selectorIndex]]
- selectorIndex++
- decoded = 0
- }
-
- v := currentHuffmanTree.Decode(br)
- decoded++
-
- if v < 2 {
- // This is either the RUNA or RUNB symbol.
- if repeat == 0 {
- repeat_power = 1
- }
- repeat += repeat_power << v
- repeat_power <<= 1
-
- // This limit of 2 million comes from the bzip2 source
- // code. It prevents repeat from overflowing.
- if repeat > 2*1024*1024 {
- return StructuralError("repeat count too large")
- }
- continue
- }
-
- if repeat > 0 {
- // We have decoded a complete run-length so we need to
- // replicate the last output symbol.
- if repeat > bz2.blockSize-bufIndex {
- return StructuralError("repeats past end of block")
- }
- for i := 0; i < repeat; i++ {
- b := byte(mtf.First())
- bz2.tt[bufIndex] = uint32(b)
- bz2.c[b]++
- bufIndex++
- }
- repeat = 0
- }
-
- if int(v) == numSymbols-1 {
- // This is the EOF symbol. Because it's always at the
- // end of the move-to-front list, and never gets moved
- // to the front, it has this unique value.
- break
- }
-
- // Since two metasymbols (RUNA and RUNB) have values 0 and 1,
- // one would expect |v-2| to be passed to the MTF decoder.
- // However, the front of the MTF list is never referenced as 0,
- // it's always referenced with a run-length of 1. Thus 0
- // doesn't need to be encoded and we have |v-1| in the next
- // line.
- b := byte(mtf.Decode(int(v - 1)))
- if bufIndex >= bz2.blockSize {
- return StructuralError("data exceeds block size")
- }
- bz2.tt[bufIndex] = uint32(b)
- bz2.c[b]++
- bufIndex++
- }
-
- if origPtr >= uint(bufIndex) {
- return StructuralError("origPtr out of bounds")
- }
-
- // We have completed the entropy decoding. Now we can perform the
- // inverse BWT and setup the RLE buffer.
- bz2.preRLE = bz2.tt[:bufIndex]
- bz2.preRLEUsed = 0
- bz2.tPos = inverseBWT(bz2.preRLE, origPtr, bz2.c[:])
- bz2.lastByte = -1
- bz2.byteRepeats = 0
- bz2.repeats = 0
-
- return nil
-}
-
-// inverseBWT implements the inverse Burrows-Wheeler transform as described in
-// http://www.hpl.hp.com/techreports/Compaq-DEC/SRC-RR-124.pdf, section 4.2.
-// In that document, origPtr is called `I' and c is the `C' array after the
-// first pass over the data. It's an argument here because we merge the first
-// pass with the Huffman decoding.
-//
-// This also implements the `single array' method from the bzip2 source code
-// which leaves the output, still shuffled, in the bottom 8 bits of tt with the
-// index of the next byte in the top 24-bits. The index of the first byte is
-// returned.
-func inverseBWT(tt []uint32, origPtr uint, c []uint) uint32 {
- sum := uint(0)
- for i := 0; i < 256; i++ {
- sum += c[i]
- c[i] = sum - c[i]
- }
-
- for i := range tt {
- b := tt[i] & 0xff
- tt[c[b]] |= uint32(i) << 8
- c[b]++
- }
-
- return tt[origPtr] >> 8
-}
-
-// This is a standard CRC32 like in hash/crc32 except that all the shifts are reversed,
-// causing the bits in the input to be processed in the reverse of the usual order.
-
-var crctab [256]uint32
-
-func init() {
- const poly = 0x04C11DB7
- for i := range crctab {
- crc := uint32(i) << 24
- for j := 0; j < 8; j++ {
- if crc&0x80000000 != 0 {
- crc = (crc << 1) ^ poly
- } else {
- crc <<= 1
- }
- }
- crctab[i] = crc
- }
-}
-
-// updateCRC updates the crc value to incorporate the data in b.
-// The initial value is 0.
-func updateCRC(val uint32, b []byte) uint32 {
- crc := ^val
- for _, v := range b {
- crc = crctab[byte(crc>>24)^v] ^ (crc << 8)
- }
- return ^crc
-}
generated by cgit v1.2.3 (git 2.39.1) at 2025-04-29 09:25:54 +0000