(一)简要介绍
去官网下载之http://code.google.com/p/snappy/。在ProjectHome处有这么一段英文,我想许多地方都引用和翻译了这段。我也尝试翻译一下。
Snappyisacompression/decompressionlibrary.
Itdoesnotaimformaximumcompression,
orcompatibilitywithanyothercompressionlibrary;
instead,itaimsforveryhighspeedsandreasonablecompression.
Forinstance,comparedtothefastestmodeofzlib,
Snappyisanorderofmagnitudefasterformostinputs,
buttheresultingcompressedfilesareanywherefrom20%to100%bigger.
OnasinglecoreofaCorei7processorin64-bitmode,
Snappycompressesatabout250MB/secormoreand
decompressesatabout500MB/secormore.
SnappyiswidelyusedinsideGoogle,ineverythingfromBigTable
andMapReducetoourinternalRPCsystems.
译文:Snappy是一个压缩/解压缩库。它不是以最大压缩率,或者与其他压缩库兼容为目标;它旨在获得高速的压缩和合理的压缩率。例如,Snappy对大多数的输入比zlib的最快模式要快几个数量级,但是其压缩过后的文件通常会比zlib大20%到100%。在Corei7的单核64位模式下,Snappy压缩速度大概可以达到250MB/s或者更快,解压缩可以达到大约500MB/s或更快。
Snappy在Google内部广泛使用,从BigTable,MapReduce到公司内部的RPC系统。
(二)安装过程
下面描述安装过程:
下载snappy-1.0.5.tar.gz,snappy的安装过程与传统的安装过程一样。解压后的INSTALL文件有详细的安装说明。
gunzipsnappy-1.0.5.tar.gz
tarxfsnappy-1.0.5.tar
cdsnappy-1.0.5
./configure
make
makeinstall
安装完成后,生成的动态库和静态库位于/usr/local/lib处,编程需要用到的头文件位于/usr/local/include处。注意需要将这些库文件cp至/usr/lib处,不然就算在链接的时候加上-L/usr/local/lib,在运行时也会报错。./main:errorwhileloadingsharedlibraries:libsnappy.so.1:
cannotopensharedobjectfile:Nosuchfileordirectory
当然这是我的LD_LIBRARY_PATH环境变量的设置问题。
(三)使用snappy
解压出来的README文件介绍了一简单的使用方式。snappy是各种库标示符所在的命名空间。C++使用需要包含#include
snappy.h
// Copyright 2005 and onwards Google Inc.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
//
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * Redistributions in binary form must reproduce the above
// copyright notice, this list of conditions and the following disclaimer
// in the documentation and/or other materials provided with the
// distribution.
// * Neither the name of Google Inc. nor the names of its
// contributors may be used to endorse or promote products derived from
// this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//
// A light-weight compression algorithm. It is designed for speed of
// compression and decompression, rather than for the utmost in space
// savings.
//
// For getting better compression ratios when you are compressing data
// with long repeated sequences or compressing data that is similar to
// other data, while still compressing fast, you might look at first
// using BMDiff and then compressing the output of BMDiff with
// Snappy.
#ifndef UTIL_SNAPPY_SNAPPY_H__
#define UTIL_SNAPPY_SNAPPY_H__
#include
#include
#include "snappy-stubs-public.h"
namespace snappy {
class Source;
class Sink;
// ------------------------------------------------------------------------
// Generic compression/decompression routines.
// ------------------------------------------------------------------------
// Compress the bytes read from "*source" and append to "*sink". Return the
// number of bytes written.
size_t Compress(Source* source, Sink* sink);
bool GetUncompressedLength(Source* source, uint32* result);
// ------------------------------------------------------------------------
// Higher-level string based routines (should be sufficient for most users)
// ------------------------------------------------------------------------
// Sets "*output" to the compressed version of "input[0,input_length-1]".
// Original contents of *output are lost.
//
// REQUIRES: "input[]" is not an alias of "*output".
size_t Compress(const char* input, size_t input_length, string* output);
// Decompresses "compressed[0,compressed_length-1]" to "*uncompressed".
// Original contents of "*uncompressed" are lost.
//
// REQUIRES: "compressed[]" is not an alias of "*uncompressed".
//
// returns false if the message is corrupted and could not be decompressed
bool Uncompress(const char* compressed, size_t compressed_length,
string* uncompressed);
// ------------------------------------------------------------------------
// Lower-level character array based routines. May be useful for
// efficiency reasons in certain circumstances.
// ------------------------------------------------------------------------
// REQUIRES: "compressed" must point to an area of memory that is at
// least "MaxCompressedLength(input_length)" bytes in length.
//
// Takes the data stored in "input[0..input_length]" and stores
// it in the array pointed to by "compressed".
//
// "*compressed_length" is set to the length of the compressed output.
//
// Example:
// char* output = new char[snappy::MaxCompressedLength(input_length)];
// size_t output_length;
// RawCompress(input, input_length, output, &output_length);
// ... Process(output, output_length) ...
// delete [] output;
void RawCompress(const char* input,
size_t input_length,
char* compressed,
size_t* compressed_length);
// Given data in "compressed[0..compressed_length-1]" generated by
// calling the Snappy::Compress routine, this routine
// stores the uncompressed data to
// uncompressed[0..GetUncompressedLength(compressed)-1]
// returns false if the message is corrupted and could not be decrypted
bool RawUncompress(const char* compressed, size_t compressed_length,
char* uncompressed);
// Given data from the byte source 'compressed' generated by calling
// the Snappy::Compress routine, this routine stores the uncompressed
// data to
// uncompressed[0..GetUncompressedLength(compressed,compressed_length)-1]
// returns false if the message is corrupted and could not be decrypted
bool RawUncompress(Source* compressed, char* uncompressed);
// Returns the maximal size of the compressed representation of
// input data that is "source_bytes" bytes in length;
size_t MaxCompressedLength(size_t source_bytes);
// REQUIRES: "compressed[]" was produced by RawCompress() or Compress()
// Returns true and stores the length of the uncompressed data in
// *result normally. Returns false on parsing error.
// This operation takes O(1) time.
bool GetUncompressedLength(const char* compressed, size_t compressed_length,
size_t* result);
// Returns true iff the contents of "compressed[]" can be uncompressed
// successfully. Does not return the uncompressed data. Takes
// time proportional to compressed_length, but is usually at least
// a factor of four faster than actual decompression.
bool IsValidCompressedBuffer(const char* compressed,
size_t compressed_length);
// *** DO NOT CHANGE THE VALUE OF kBlockSize ***
//
// New Compression code chops up the input into blocks of at most
// the following size. This ensures that back-references in the
// output never cross kBlockSize block boundaries. This can be
// helpful in implementing blocked decompression. However the
// decompression code should not rely on this guarantee since older
// compression code may not obey it.
static const int kBlockLog = 15;
static const size_t kBlockSize = 1 << kBlockLog;
static const int kMaxHashTableBits = 14;
static const size_t kMaxHashTableSize = 1 << kMaxHashTableBits;
} // end namespace snappy
#endif // UTIL_SNAPPY_SNAPPY_H__
snapp-c.h
/*
* Copyright 2011 Martin Gieseking .
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are
* met:
*
* * Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above
* copyright notice, this list of conditions and the following disclaimer
* in the documentation and/or other materials provided with the
* distribution.
* * Neither the name of Google Inc. nor the names of its
* contributors may be used to endorse or promote products derived from
* this software without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*
* Plain C interface (a wrapper around the C++ implementation).
*/
#ifndef UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_
#define UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_
#ifdef __cplusplus
extern "C" {
#endif
#include
/*
* Return values; see the documentation for each function to know
* what each can return.
*/
typedef enum {
SNAPPY_OK = 0,
SNAPPY_INVALID_INPUT = 1,
SNAPPY_BUFFER_TOO_SMALL = 2,
} snappy_status;
/*
* Takes the data stored in "input[0..input_length-1]" and stores
* it in the array pointed to by "compressed".
*
* signals the space available in "compressed".
* If it is not at least equal to "snappy_max_compressed_length(input_length)",
* SNAPPY_BUFFER_TOO_SMALL is returned. After successful compression,
* contains the true length of the compressed output,
* and SNAPPY_OK is returned.
*
* Example:
* size_t output_length = snappy_max_compressed_length(input_length);
* char* output = (char*)malloc(output_length);
* if (snappy_compress(input, input_length, output, &output_length)
* == SNAPPY_OK) {
* ... Process(output, output_length) ...
* }
* free(output);
*/
snappy_status snappy_compress(const char* input,
size_t input_length,
char* compressed,
size_t* compressed_length);
/*
* Given data in "compressed[0..compressed_length-1]" generated by
* calling the snappy_compress routine, this routine stores
* the uncompressed data to
* uncompressed[0..uncompressed_length-1].
* Returns failure (a value not equal to SNAPPY_OK) if the message
* is corrupted and could not be decrypted.
*
* signals the space available in "uncompressed".
* If it is not at least equal to the value returned by
* snappy_uncompressed_length for this stream, SNAPPY_BUFFER_TOO_SMALL
* is returned. After successful decompression,
* contains the true length of the decompressed output.
*
* Example:
* size_t output_length;
* if (snappy_uncompressed_length(input, input_length, &output_length)
* != SNAPPY_OK) {
* ... fail ...
* }
* char* output = (char*)malloc(output_length);
* if (snappy_uncompress(input, input_length, output, &output_length)
* == SNAPPY_OK) {
* ... Process(output, output_length) ...
* }
* free(output);
*/
snappy_status snappy_uncompress(const char* compressed,
size_t compressed_length,
char* uncompressed,
size_t* uncompressed_length);
/*
* Returns the maximal size of the compressed representation of
* input data that is "source_length" bytes in length.
*/
size_t snappy_max_compressed_length(size_t source_length);
/*
* REQUIRES: "compressed[]" was produced by snappy_compress()
* Returns SNAPPY_OK and stores the length of the uncompressed data in
* *result normally. Returns SNAPPY_INVALID_INPUT on parsing error.
* This operation takes O(1) time.
*/
snappy_status snappy_uncompressed_length(const char* compressed,
size_t compressed_length,
size_t* result);
/*
* Check if the contents of "compressed[]" can be uncompressed successfully.
* Does not return the uncompressed data; if so, returns SNAPPY_OK,
* or if not, returns SNAPPY_INVALID_INPUT.
* Takes time proportional to compressed_length, but is usually at least a
* factor of four faster than actual decompression.
*/
snappy_status snappy_validate_compressed_buffer(const char* compressed,
size_t compressed_length);
#ifdef __cplusplus
} // extern "C"
#endif
#endif /* UTIL_SNAPPY_OPENSOURCE_SNAPPY_C_H_ */