289b30715d
This commit converts the dependency management from Godeps to the vendor folder, also switching the tool from godep to trash. Since the upstream tool lacks a few features proposed via a few PRs, until those PRs are merged in (if), use github.com/karalabe/trash. You can update dependencies via trash --update. All dependencies have been updated to their latest version. Parts of the build system are reworked to drop old notions of Godeps and invocation of the go vet command so that it doesn't run against the vendor folder, as that will just blow up during vetting. The conversion drops OpenCL (and hence GPU mining support) from ethash and our codebase. The short reasoning is that there's noone to maintain and having opencl libs in our deps messes up builds as go install ./... tries to build them, failing with unsatisfied link errors for the C OpenCL deps. golang.org/x/net/context is not vendored in. We expect it to be fetched by the user (i.e. using go get). To keep ci.go builds reproducible the package is "vendored" in build/_vendor.
88 lines
3.3 KiB
Go
88 lines
3.3 KiB
Go
// Copyright 2011 The Snappy-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 snappy implements the snappy block-based compression format.
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// It aims for very high speeds and reasonable compression.
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//
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// The C++ snappy implementation is at https://github.com/google/snappy
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package snappy // import "github.com/golang/snappy"
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import (
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"hash/crc32"
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)
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/*
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Each encoded block begins with the varint-encoded length of the decoded data,
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followed by a sequence of chunks. Chunks begin and end on byte boundaries. The
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first byte of each chunk is broken into its 2 least and 6 most significant bits
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called l and m: l ranges in [0, 4) and m ranges in [0, 64). l is the chunk tag.
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Zero means a literal tag. All other values mean a copy tag.
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For literal tags:
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- If m < 60, the next 1 + m bytes are literal bytes.
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- Otherwise, let n be the little-endian unsigned integer denoted by the next
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m - 59 bytes. The next 1 + n bytes after that are literal bytes.
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For copy tags, length bytes are copied from offset bytes ago, in the style of
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Lempel-Ziv compression algorithms. In particular:
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- For l == 1, the offset ranges in [0, 1<<11) and the length in [4, 12).
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The length is 4 + the low 3 bits of m. The high 3 bits of m form bits 8-10
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of the offset. The next byte is bits 0-7 of the offset.
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- For l == 2, the offset ranges in [0, 1<<16) and the length in [1, 65).
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The length is 1 + m. The offset is the little-endian unsigned integer
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denoted by the next 2 bytes.
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- For l == 3, this tag is a legacy format that is no longer issued by most
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encoders. Nonetheless, the offset ranges in [0, 1<<32) and the length in
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[1, 65). The length is 1 + m. The offset is the little-endian unsigned
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integer denoted by the next 4 bytes.
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*/
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const (
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tagLiteral = 0x00
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tagCopy1 = 0x01
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tagCopy2 = 0x02
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tagCopy4 = 0x03
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)
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const (
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checksumSize = 4
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chunkHeaderSize = 4
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magicChunk = "\xff\x06\x00\x00" + magicBody
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magicBody = "sNaPpY"
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// maxBlockSize is the maximum size of the input to encodeBlock. It is not
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// part of the wire format per se, but some parts of the encoder assume
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// that an offset fits into a uint16.
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//
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// Also, for the framing format (Writer type instead of Encode function),
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// https://github.com/google/snappy/blob/master/framing_format.txt says
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// that "the uncompressed data in a chunk must be no longer than 65536
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// bytes".
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maxBlockSize = 65536
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// maxEncodedLenOfMaxBlockSize equals MaxEncodedLen(maxBlockSize), but is
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// hard coded to be a const instead of a variable, so that obufLen can also
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// be a const. Their equivalence is confirmed by
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// TestMaxEncodedLenOfMaxBlockSize.
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maxEncodedLenOfMaxBlockSize = 76490
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obufHeaderLen = len(magicChunk) + checksumSize + chunkHeaderSize
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obufLen = obufHeaderLen + maxEncodedLenOfMaxBlockSize
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)
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const (
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chunkTypeCompressedData = 0x00
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chunkTypeUncompressedData = 0x01
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chunkTypePadding = 0xfe
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chunkTypeStreamIdentifier = 0xff
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)
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var crcTable = crc32.MakeTable(crc32.Castagnoli)
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// crc implements the checksum specified in section 3 of
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// https://github.com/google/snappy/blob/master/framing_format.txt
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func crc(b []byte) uint32 {
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c := crc32.Update(0, crcTable, b)
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return uint32(c>>15|c<<17) + 0xa282ead8
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}
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