alphanum.hpp

#ifndef ALPHANUM__HPP
#define ALPHANUM__HPP

/*
   The Alphanum Algorithm is an improved sorting algorithm for strings
   containing numbers.  Instead of sorting numbers in ASCII order like a
   standard sort, this algorithm sorts numbers in numeric order.

   The Alphanum Algorithm is discussed at http://www.DaveKoelle.com

   This implementation is Copyright (c) 2008 Dirk Jagdmann <doj@cubic.org>.
   It is a cleanroom implementation of the algorithm and not derived by
   other's works. In contrast to the versions written by Dave Koelle this
   source code is distributed with the libpng/zlib license.

   This software is provided 'as-is', without any express or implied
   warranty. In no event will the authors be held liable for any damages
   arising from the use of this software.

   Permission is granted to anyone to use this software for any purpose,
   including commercial applications, and to alter it and redistribute it
   freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you
   must not claim that you wrote the original software. If you use
   this software in a product, an acknowledgment in the product
   documentation would be appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and
   must not be misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
   distribution. */

/* $Header: /code/doj/alphanum.hpp,v 1.3 2008/01/28 23:06:47 doj Exp $ */

#include <cassert>
#include <functional>
#include <string>
#include <sstream>

#ifdef ALPHANUM_LOCALE
#include <cctype>
#endif

// TODO: make comparison with hexadecimal numbers. Extend the alphanum_comp() function by traits to choose between decimal and hexadecimal.

namespace doj {

  // anonymous namespace for functions we use internally. But if you
  // are coding in C, you can use alphanum_impl() directly, since it
  // uses not C++ features.
  namespace {

    // if you want to honour the locale settings for detecting digit
    // characters, you should define ALPHANUM_LOCALE
#ifdef ALPHANUM_LOCALE
    /** wrapper function for ::isdigit() */
    inline
      bool alphanum_isdigit(int c)
      {
        return isdigit(c);
      }
#else

    /** this function does not consider the current locale and only
      works with ASCII digits.
      @return true if c is a digit character
      */
    inline
      bool alphanum_isdigit( const char c ) {
        return c >= '0' && c <= '9';
      }

#endif

    /**
      compare l and r with strcmp() semantics, but using
      the "Alphanum Algorithm". This function is designed to read
      through the l and r strings only one time, for
      maximum performance. It does not allocate memory for
      substrings. It can either use the C-library functions isdigit()
      and atoi() to honour your locale settings, when recognizing
      digit characters when you "#define ALPHANUM_LOCALE=1" or use
      it's own digit character handling which only works with ASCII
      digit characters, but provides better performance.

      @param l NULL-terminated C-style string
      @param r NULL-terminated C-style string
      @return negative if l<r, 0 if l equals r, positive if l>r
      */
    inline
      int alphanum_impl( const char * l, const char * r ) {
        enum mode_t {
          STRING, NUMBER
        } mode = STRING;

        while ( *l && *r ) {
          if ( mode == STRING ) {
            char l_char, r_char;
            while ( ( l_char = *l ) && ( r_char = *r ) ) {
              // check if this are digit characters
              const bool l_digit = alphanum_isdigit( l_char ), r_digit = alphanum_isdigit( r_char );
              // if both characters are digits, we continue in NUMBER mode
              if ( l_digit && r_digit ) {
                mode = NUMBER;
                break;
              }
              // if only the left character is a digit, we have a result
              if ( l_digit ) return -1;
              // if only the right character is a digit, we have a result
              if ( r_digit ) return +1;
              // compute the difference of both characters
              const int diff = l_char - r_char;
              // if they differ we have a result
              if ( diff != 0 ) return diff;
              // otherwise process the next characters
              ++l;
              ++r;
            }
          }
          else // mode==NUMBER
          {
            // In case we have no diffs, we need to check the len, because you could have a different numbers of leading zeros
            unsigned int l_len = 0;
            unsigned int r_len = 0;

#ifdef ALPHANUM_LOCALE
            // get the left number
            char *end;
            unsigned long l_int=strtoul(l, &end, 0);
            l_len = end - l;
            l=end;

            // get the right number
            unsigned long r_int=strtoul(r, &end, 0);
            r_len = end - r;
            r=end;
#else
            // Here, as soon as we find something that's isn't zero, everything will start
            // to get shifted, eg "0012" will give 12
            // get the left number
            unsigned long l_int = 0;
            while ( *l && alphanum_isdigit( *l ) ) {
              // TODO: this can overflow
              l_int = l_int * 10 + *l - '0';
              ++l;
              ++l_len;
            }

            // get the right number
            unsigned long r_int = 0;
            while ( *r && alphanum_isdigit( *r ) ) {
              // TODO: this can overflow
              r_int = r_int * 10 + *r - '0';
              ++r;
              ++r_len;
            }
#endif

            // if the difference is not equal to zero, we have a comparison result
            const long diff = l_int - r_int;
            if ( diff != 0 ) {
              return diff;
            }

            // If we get here, whoever is the longest has more leading zeros
            // and I assume we want "01" to be returned as less than "1"
            // if left character length is greater than right, we have a result
            if ( l_len < r_len ) return +1;
            // if right character length is greater than left, we have a result
            if ( l_len > r_len ) return -1;

            // otherwise we process the next substring in STRING mode
            mode = STRING;
          }
        }

        if ( *r ) return -1;
        if ( *l ) return +1;
        return 0;
      }

  }

  /**
    Compare left and right with the same semantics as strcmp(), but with the
    "Alphanum Algorithm" which produces more human-friendly
    results. The classes lT and rT must implement "std::ostream
    operator<< (std::ostream&, const Ty&)".

    @return negative if left<right, 0 if left==right, positive if left>right.
    */
  template < typename lT, typename rT >
    inline
    int alphanum_comp( const lT & left, const rT & right ) {
      std::ostringstream l;
      l << left;
      std::ostringstream r;
      r << right;
      return alphanum_impl( l.str().c_str(), r.str().c_str() );
    }

  /**
    Compare l and r with the same semantics as strcmp(), but with
    the "Alphanum Algorithm" which produces more human-friendly
    results.

    @return negative if l<r, 0 if l==r, positive if l>r.
    */
  template <>
    inline
    int alphanum_comp < std::string >( const std::string & l, const std::string & r ) {
      return alphanum_impl( l.c_str(), r.c_str() );
    }

  ////////////////////////////////////////////////////////////////////////////

  // now follow a lot of overloaded alphanum_comp() functions to get a
  // direct call to alphanum_impl() upon the various combinations of c
  // and c++ strings.

  /**
    Compare l and r with the same semantics as strcmp(), but with
    the "Alphanum Algorithm" which produces more human-friendly
    results.

    @return negative if l<r, 0 if l==r, positive if l>r.
    */
  inline
    int alphanum_comp( char * l, char * r ) {
      assert( l );
      assert( r );
      return alphanum_impl( l, r );
    }

  inline
    int alphanum_comp( const char * l, const char * r ) {
      assert( l );
      assert( r );
      return alphanum_impl( l, r );
    }

  inline
    int alphanum_comp( char * l, const char * r ) {
      assert( l );
      assert( r );
      return alphanum_impl( l, r );
    }

  inline
    int alphanum_comp( const char * l, char * r ) {
      assert( l );
      assert( r );
      return alphanum_impl( l, r );
    }

  inline
    int alphanum_comp( const std::string & l, char * r ) {
      assert( r );
      return alphanum_impl( l.c_str(), r );
    }

  inline
    int alphanum_comp( char * l, const std::string & r ) {
      assert( l );
      return alphanum_impl( l, r.c_str() );
    }

  inline
    int alphanum_comp( const std::string & l, const char * r ) {
      assert( r );
      return alphanum_impl( l.c_str(), r );
    }

  inline
    int alphanum_comp( const char * l, const std::string & r ) {
      assert( l );
      return alphanum_impl( l, r.c_str() );
    }

  ////////////////////////////////////////////////////////////////////////////

  /**
    Functor class to compare two objects with the "Alphanum
    Algorithm". If the objects are no std::string, they must
    implement "std::ostream operator<< (std::ostream&, const Ty&)".
    */
  template < class Ty = void >
    struct alphanum_less  {
      bool operator()( const Ty & left, const Ty & right ) const {
        return alphanum_comp( left, right ) < 0;
      }
    };

  template <>
    struct alphanum_less<void> {
      template<typename LHS, typename RHS>
      bool operator()(const LHS& left, const RHS& right) const {
        return alphanum_comp(left, right) < 0;
      }
    };

}

#endif