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前往新版Gitcode,体验更适合开发者的 AI 搜索 >>
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fd5d51c9
编写于
5月 05, 2017
作者:
Z
Zsolt Felfoldi
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电子邮件补丁
差异文件
common/bitutil: added data compression algorithm
上级
2ec5cf16
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1
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common/bitutil/compress.go
common/bitutil/compress.go
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common/bitutil/compress.go
0 → 100644
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// Copyright 2017 The go-ethereum Authors
// This file is part of the go-ethereum library.
//
// The go-ethereum library is free software: you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// The go-ethereum library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
package
bitutil
/*
The compression algorithm implemented by CompressBytes and DecompressBytes is
optimized for "sparse" input data which contains a lot of zero bytes. Decompression
requires knowledge of the decompressed data length. Compression works as follows:
if data only contains zeroes,
CompressBytes(data) == nil
otherwise if len(data) <= 1,
CompressBytes(data) == data
otherwise:
CompressBytes(data) == append(CompressBytes(nonZeroBits(data)), nonZeroBytes(data)...)
where
nonZeroBits(data) is a bit vector with len(data) bits (MSB first):
nonZeroBits(data)[i/8] && (1 << (7-i%8)) != 0 if data[i] != 0
len(nonZeroBits(data)) == (len(data)+7)/8
nonZeroBytes(data) contains the non-zero bytes of data in the same order
*/
// CompressBytes compresses the input byte slice
func
CompressBytes
(
data
[]
byte
)
[]
byte
{
if
len
(
data
)
==
0
{
return
nil
}
if
len
(
data
)
==
1
{
if
data
[
0
]
==
0
{
return
nil
}
else
{
return
data
}
}
bitsLen
:=
(
len
(
data
)
+
7
)
/
8
nonZeroBits
:=
make
([]
byte
,
bitsLen
)
nonZeroBytes
:=
make
([]
byte
,
0
,
len
(
data
))
for
i
,
b
:=
range
data
{
if
b
!=
0
{
nonZeroBytes
=
append
(
nonZeroBytes
,
b
)
nonZeroBits
[
i
/
8
]
|=
1
<<
byte
(
7
-
i
%
8
)
}
}
if
len
(
nonZeroBytes
)
==
0
{
return
nil
}
return
append
(
CompressBytes
(
nonZeroBits
),
nonZeroBytes
...
)
}
// DecompressBytes decompresses data with a known target size.
// In addition to the decompressed output, the function returns the length of
// compressed input data corresponding to the output. The input slice may be longer.
// If the input slice is too short, (nil, -1) is returned.
func
DecompressBytes
(
data
[]
byte
,
targetLen
int
)
([]
byte
,
int
)
{
decomp
:=
make
([]
byte
,
targetLen
)
if
len
(
data
)
==
0
{
return
decomp
,
0
}
if
targetLen
==
1
{
return
data
[
0
:
1
],
1
}
bitsLen
:=
(
targetLen
+
7
)
/
8
nonZeroBits
,
ptr
:=
DecompressBytes
(
data
,
bitsLen
)
if
ptr
<
0
{
return
nil
,
-
1
}
for
i
,
_
:=
range
decomp
{
if
nonZeroBits
[
i
/
8
]
&
(
1
<<
byte
(
7
-
i
%
8
))
!=
0
{
if
ptr
==
len
(
data
)
{
return
nil
,
-
1
}
decomp
[
i
]
=
data
[
ptr
]
ptr
++
}
}
return
decomp
,
ptr
}
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