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/** @file byte_length_strings.h
* @brief Handle decoding lists of strings with byte lengths
*/
/* Copyright (C) 2004,2005,2006,2007,2008,2009,2010 Olly Betts
*
* 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 WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. 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 XAPIAN_INCLUDED_BYTE_LENGTH_STRINGS_H
#define XAPIAN_INCLUDED_BYTE_LENGTH_STRINGS_H
#include <xapian/error.h>
#include <string>
// We XOR the length values with this so that they are more likely to coincide
// with lower case ASCII letters, which are likely to be common. This means
// that zlib should do a better job of compressing tag values - in tests, this
// gave 5% better compression.
#define MAGIC_XOR_VALUE 96
class ByteLengthPrefixedStringItor {
const unsigned char * p;
size_t left;
ByteLengthPrefixedStringItor(const unsigned char * p_, size_t left_)
: p(p_), left(left_) { }
public:
explicit ByteLengthPrefixedStringItor(const std::string & s)
: p(reinterpret_cast<const unsigned char *>(s.data())),
left(s.size()) { }
std::string operator*() const {
size_t len = *p ^ MAGIC_XOR_VALUE;
return std::string(reinterpret_cast<const char *>(p + 1), len);
}
ByteLengthPrefixedStringItor operator++(int) {
const unsigned char * old_p = p;
size_t old_left = left;
operator++();
return ByteLengthPrefixedStringItor(old_p, old_left);
}
ByteLengthPrefixedStringItor & operator++() {
if (!left) {
throw Xapian::DatabaseCorruptError("Bad synonym data (none left)");
}
size_t add = (*p ^ MAGIC_XOR_VALUE) + 1;
if (left < add) {
throw Xapian::DatabaseCorruptError("Bad synonym data (too little left)");
}
p += add;
left -= add;
return *this;
}
bool at_end() const {
return left == 0;
}
};
struct ByteLengthPrefixedStringItorGt {
/// Return true if and only if a's string is strictly greater than b's.
bool operator()(const ByteLengthPrefixedStringItor *a,
const ByteLengthPrefixedStringItor *b) const {
return (**a > **b);
}
};
#endif // XAPIAN_INCLUDED_BYTE_LENGTH_STRINGS_H
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