mirror of
https://github.com/go-gitea/gitea
synced 2025-11-04 05:18:25 +00:00
b6a95a8cb3
* Dropped unused codekit config * Integrated dynamic and static bindata for public * Ignore public bindata * Add a general generate make task * Integrated flexible public assets into web command * Updated vendoring, added all missiong govendor deps * Made the linter happy with the bindata and dynamic code * Moved public bindata definition to modules directory * Ignoring the new bindata path now * Updated to the new public modules import path * Updated public bindata command and drop the new prefix
85 lines
3.1 KiB
Go
85 lines
3.1 KiB
Go
// Copyright 2011 The Snappy-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 snappy implements the snappy block-based compression format.
|
|
// It aims for very high speeds and reasonable compression.
|
|
//
|
|
// The C++ snappy implementation is at https://github.com/google/snappy
|
|
package snappy // import "github.com/golang/snappy"
|
|
|
|
import (
|
|
"hash/crc32"
|
|
)
|
|
|
|
/*
|
|
Each encoded block begins with the varint-encoded length of the decoded data,
|
|
followed by a sequence of chunks. Chunks begin and end on byte boundaries. The
|
|
first byte of each chunk is broken into its 2 least and 6 most significant bits
|
|
called l and m: l ranges in [0, 4) and m ranges in [0, 64). l is the chunk tag.
|
|
Zero means a literal tag. All other values mean a copy tag.
|
|
|
|
For literal tags:
|
|
- If m < 60, the next 1 + m bytes are literal bytes.
|
|
- Otherwise, let n be the little-endian unsigned integer denoted by the next
|
|
m - 59 bytes. The next 1 + n bytes after that are literal bytes.
|
|
|
|
For copy tags, length bytes are copied from offset bytes ago, in the style of
|
|
Lempel-Ziv compression algorithms. In particular:
|
|
- For l == 1, the offset ranges in [0, 1<<11) and the length in [4, 12).
|
|
The length is 4 + the low 3 bits of m. The high 3 bits of m form bits 8-10
|
|
of the offset. The next byte is bits 0-7 of the offset.
|
|
- For l == 2, the offset ranges in [0, 1<<16) and the length in [1, 65).
|
|
The length is 1 + m. The offset is the little-endian unsigned integer
|
|
denoted by the next 2 bytes.
|
|
- For l == 3, this tag is a legacy format that is no longer supported.
|
|
*/
|
|
const (
|
|
tagLiteral = 0x00
|
|
tagCopy1 = 0x01
|
|
tagCopy2 = 0x02
|
|
tagCopy4 = 0x03
|
|
)
|
|
|
|
const (
|
|
checksumSize = 4
|
|
chunkHeaderSize = 4
|
|
magicChunk = "\xff\x06\x00\x00" + magicBody
|
|
magicBody = "sNaPpY"
|
|
|
|
// maxBlockSize is the maximum size of the input to encodeBlock. It is not
|
|
// part of the wire format per se, but some parts of the encoder assume
|
|
// that an offset fits into a uint16.
|
|
//
|
|
// Also, for the framing format (Writer type instead of Encode function),
|
|
// https://github.com/google/snappy/blob/master/framing_format.txt says
|
|
// that "the uncompressed data in a chunk must be no longer than 65536
|
|
// bytes".
|
|
maxBlockSize = 65536
|
|
|
|
// maxEncodedLenOfMaxBlockSize equals MaxEncodedLen(maxBlockSize), but is
|
|
// hard coded to be a const instead of a variable, so that obufLen can also
|
|
// be a const. Their equivalence is confirmed by
|
|
// TestMaxEncodedLenOfMaxBlockSize.
|
|
maxEncodedLenOfMaxBlockSize = 76490
|
|
|
|
obufHeaderLen = len(magicChunk) + checksumSize + chunkHeaderSize
|
|
obufLen = obufHeaderLen + maxEncodedLenOfMaxBlockSize
|
|
)
|
|
|
|
const (
|
|
chunkTypeCompressedData = 0x00
|
|
chunkTypeUncompressedData = 0x01
|
|
chunkTypePadding = 0xfe
|
|
chunkTypeStreamIdentifier = 0xff
|
|
)
|
|
|
|
var crcTable = crc32.MakeTable(crc32.Castagnoli)
|
|
|
|
// crc implements the checksum specified in section 3 of
|
|
// https://github.com/google/snappy/blob/master/framing_format.txt
|
|
func crc(b []byte) uint32 {
|
|
c := crc32.Update(0, crcTable, b)
|
|
return uint32(c>>15|c<<17) + 0xa282ead8
|
|
}
|