lumiera_documentation/src/lib/symbol-impl.cpp

/*
  Symbol(impl)  -  helpers for working with literal string IDs

   Copyright (C)
     2009,2017        Hermann Vosseler <Ichthyostega@web.de>

  **Lumiera** 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. See the file COPYING for further details.

* *****************************************************************/

/** @file symbol-impl.cpp
 ** Implementation functionality to support definition of lib::Symbol.
 ** @see lib::Symbol
 ** @see control::CommandRegistry for usage example of the hash function.
 ** @see symbol-table.hpp for the implementation of _interned strings_
 */



#include "lib/symbol.hpp"
#include "lib/symbol-table.hpp"

#include <boost/functional/hash.hpp>
#include <cstddef>
#include <cstring>
#include <string>

using std::size_t;
using std::string;
using std::forward;
using boost::hash_combine;




namespace lib {
  
  const size_t STRING_MAX_RELEVANT = LUMIERA_IDSTRING_MAX_RELEVANT;
  
  namespace { // global symbol table
    
    SymbolTable&
    symbolTable()
    {
      static SymbolTable theSymbolTable;
      return theSymbolTable;  // Meyer's Singleton
    }
  }
  
  
  /**
   * create Symbol by symbol table lookup.
   * @note identical strings will be mapped to the same Symbol (embedded pointer)
   * @warning potential lock contention, since each ctor call needs to do a lookup
   * @remark since lumiera::LifecycleHook entries use a Symbol, the symbol table is
   *         implemented as Meyer's singleton and pulled up early, way before main()
   */
  Symbol::Symbol (string&& definition)
    : Literal{symbolTable().internedString (forward<string> (definition))}
    { }
  
  
  /* == predefined marker Symbols == */
  Symbol Symbol::ANY     = "*";
  Symbol Symbol::EMPTY   = "";
  Symbol Symbol::BOTTOM  = "⟂";
  Symbol Symbol::FAILURE = "↯";
  
  // see also: lib/format-obj.cpp
  // We can not share these definitions due to undefined static init order
  
  
  
  
  
  /** generate hash value based on the Literal's contents.
   *  This function is intended to be picked up by ADL, and should be usable
   *  both with  `std::hash` and `<boost/functional/hash.hpp>`. It is implemented
   *  similar as the boost::hash specialisation for std::string */
  HashVal
  hash_value (Literal literal)
  {
    size_t hash=0;
    if (literal)
      {
        size_t cnt = 1;
        CStr   pos = literal;
        for ( ; cnt <= STRING_MAX_RELEVANT and *pos ; ++cnt, ++pos )
          hash_combine (hash, *pos);
      }
    
    return hash;
  }
  
  /** hash value for Symbols is directly based on the symbol table entry */
  HashVal
  hash_value (Symbol sym)
  {
    return sym? boost::hash_value (sym.c())
              : 0;
  }
  
  
  
} // namespace lib