/usr/include/zim/zintstream.h is in libzim-dev 1.2-9.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 | /*
* Copyright (C) 2007 Tommi Maekitalo
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* is provided AS IS, WITHOUT ANY WARRANTY; without even the implied
* warranty of MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, and
* NON-INFRINGEMENT. See the GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*
*/
#ifndef ZIM_ZINTSTREAM_H
#define ZIM_ZINTSTREAM_H
#include <string>
#include <iostream>
#include <zim/zim.h>
/*
ZInt implements a int compressor and decompressor. The algorithm compresses
small values into fewer bytes.
The idea is to add information about used bytes in the first byte. The number
of additional bytes used is specified by the number of set bits counted from
the most significant bit. So the numbers 0-127 are encoded as is, since they
fit into the 7 low order bits and the high order bit specifies, that no
additional bytes are used. The number starting from 128 up to 16383 need more
than 7 bits, so we need to set the highest order bit to 1 and the next bit to
0, leaving 6 bits of actual data, which is used as the low order bits of the
number.
Since the numbers 0-127 are already encoded in one byte, the 127 is
substracted from the actual number, so a 2 byte zero is actually a 128.
The same logic continues on the 3rd, 4th, ... byte. Up to 7 additional bytes
are used, so the first byte must contain at least one 0.
binary range
------------------------------- --------------------------------------------------
0xxx xxxx 0 - 127
10xx xxxx xxxx xxxx 128 - (2^14+128-1 = 16511)
110x xxxx xxxx xxxx xxxx xxxx 16512 - (2^21+16512-1 = 2113663)
1110 xxxx xxxx xxxx xxxx xxxx xxxx xxxx
2113664 - (2^28+2113664-1 = 270549119)
...
*/
namespace zim
{
class ZIntStream
{
std::istream* _istream;
std::ostream* _ostream;
public:
/// prepare ZIntStream for compression or decompression
explicit ZIntStream(std::iostream& iostream)
: _istream(&iostream),
_ostream(&iostream)
{ }
/// prepare ZIntStream for decompression
explicit ZIntStream(std::istream& istream)
: _istream(&istream),
_ostream(0)
{ }
/// prepare ZIntStream for compression
explicit ZIntStream(std::ostream& ostream)
: _istream(0),
_ostream(&ostream)
{ }
/// decompresses one value from input stream and returns it
size_type get();
ZIntStream& get(size_type &value)
{ value = get(); return *this; }
/// compresses one value to output stream
ZIntStream& put(size_type value);
operator bool() const
{ return (_istream == 0 || *_istream)
&& (_ostream == 0 || *_ostream); }
};
}
#endif // ZIM_ZINTSTREAM_H
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