102 lines
2.5 KiB
Go
102 lines
2.5 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
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import "github.com/dsnet/compress/internal/errors"
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// rleDone is a special "error" to indicate that the RLE stage is done.
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var rleDone = errorf(errors.Unknown, "RLE1 stage is completed")
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// runLengthEncoding implements the first RLE stage of bzip2. Every sequence
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// of 4..255 duplicated bytes is replaced by only the first 4 bytes, and a
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// single byte representing the repeat length. Similar to the C bzip2
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// implementation, the encoder will always terminate repeat sequences with a
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// count (even if it is the end of the buffer), and it will also never produce
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// run lengths of 256..259. The decoder can handle the latter case.
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//
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// For example, if the input was:
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// input: "AAAAAAABBBBCCCD"
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//
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// Then the output will be:
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// output: "AAAA\x03BBBB\x00CCCD"
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type runLengthEncoding struct {
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buf []byte
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idx int
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lastVal byte
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lastCnt int
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}
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func (rle *runLengthEncoding) Init(buf []byte) {
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*rle = runLengthEncoding{buf: buf}
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}
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func (rle *runLengthEncoding) Write(buf []byte) (int, error) {
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for i, b := range buf {
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if rle.lastVal != b {
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rle.lastCnt = 0
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}
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rle.lastCnt++
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switch {
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case rle.lastCnt < 4:
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if rle.idx >= len(rle.buf) {
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return i, rleDone
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}
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rle.buf[rle.idx] = b
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rle.idx++
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case rle.lastCnt == 4:
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if rle.idx+1 >= len(rle.buf) {
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return i, rleDone
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}
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rle.buf[rle.idx] = b
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rle.idx++
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rle.buf[rle.idx] = 0
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rle.idx++
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case rle.lastCnt < 256:
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rle.buf[rle.idx-1]++
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default:
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if rle.idx >= len(rle.buf) {
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return i, rleDone
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}
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rle.lastCnt = 1
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rle.buf[rle.idx] = b
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rle.idx++
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}
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rle.lastVal = b
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}
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return len(buf), nil
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}
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func (rle *runLengthEncoding) Read(buf []byte) (int, error) {
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for i := range buf {
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switch {
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case rle.lastCnt == -4:
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if rle.idx >= len(rle.buf) {
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return i, errorf(errors.Corrupted, "missing terminating run-length repeater")
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}
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rle.lastCnt = int(rle.buf[rle.idx])
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rle.idx++
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if rle.lastCnt > 0 {
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break // Break the switch
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}
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fallthrough // Count was zero, continue the work
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case rle.lastCnt <= 0:
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if rle.idx >= len(rle.buf) {
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return i, rleDone
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}
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b := rle.buf[rle.idx]
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rle.idx++
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if b != rle.lastVal {
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rle.lastCnt = 0
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rle.lastVal = b
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}
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}
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buf[i] = rle.lastVal
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rle.lastCnt--
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}
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return len(buf), nil
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}
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func (rle *runLengthEncoding) Bytes() []byte { return rle.buf[:rle.idx] }
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