mpw/bin/intern.cpp

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#include "intern.h"
#include <unordered_map>
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#include <cstring>
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namespace {
std::unordered_multimap<unsigned, std::string *> InternTable;
std::string EmptyString;
unsigned int DJBHash(const char* begin, size_t length)
{
unsigned int hash = 5381;
for(size_t i = 0; i < length; ++i)
{
hash = ((hash << 5) + hash) + (begin[i]);
}
return hash;
}
}
namespace Intern {
const std::string *String(std::string &&str)
{
size_t size = str.size();
if (!size) return &EmptyString;
unsigned hash = DJBHash(str.data(), size);
auto range = InternTable.equal_range(hash);
auto iter = range.first;
auto endit = range.second;
for( ; iter != endit; ++iter)
{
// hash matches, make sure the string does.
const std::string *s = iter->second;
if (s->size() == size && std::memcmp(s->data(), str.data(), size) == 0)
return s;
}
// insert it. I suppose this could throw, in which case a string would leak.
std::string *s = new std::string(std::move(str));
InternTable.emplace(std::make_pair(hash, s));
return s;
}
const std::string *String(const char *begin, size_t size)
{
if (!size) return &EmptyString;
unsigned hash = DJBHash(begin, size);
auto range = InternTable.equal_range(hash);
auto iter = range.first;
auto endit = range.second;
for( ; iter != endit; ++iter)
{
// hash matches, make sure the string does.
const std::string *s = iter->second;
if (s->size() == size && std::memcmp(s->data(), begin, size) == 0)
return s;
}
// insert it. I suppose this could throw, in which case a string would leak.
std::string *s = new std::string(begin, size);
InternTable.emplace(std::make_pair(hash, s));
return s;
}
const std::string *String(const char *begin, const char *end)
{
return String(begin, end - begin);
}
const std::string *String(const char *cp)
{
if (!cp || !*cp) return &EmptyString;
return String(cp, strlen(cp));
}
const std::string *String(const std::string &s)
{
return String(s.data(), s.size());
}
}