text: 
  /* ***** BEGIN LICENSE BLOCK *****
   * Version: MPL 1.1/GPL 2.0/LGPL 2.1
   *
   * The contents of this file are subject to the Mozilla Public License Version
   * 1.1 (the "License"); you may not use this file except in compliance with
   * the License. You may obtain a copy of the License at
   * http://www.mozilla.org/MPL/
   *
   * Software distributed under the License is distributed on an "AS IS" basis,
   * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
   * for the specific language governing rights and limitations under the
   * License.
   *
   * The Original Code is libguac.
   *
   * The Initial Developer of the Original Code is
   * Michael Jumper.
   * Portions created by the Initial Developer are Copyright (C) 2010
   * the Initial Developer. All Rights Reserved.
   *
   * Contributor(s):
   *
   * Alternatively, the contents of this file may be used under the terms of
   * either the GNU General Public License Version 2 or later (the "GPL"), or
   * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
   * in which case the provisions of the GPL or the LGPL are applicable instead
   * of those above. If you wish to allow use of your version of this file only
   * under the terms of either the GPL or the LGPL, and not to allow others to
   * use your version of this file under the terms of the MPL, indicate your
   * decision by deleting the provisions above and replace them with the notice
   * and other provisions required by the GPL or the LGPL. If you do not delete
   * the provisions above, a recipient may use your version of this file under
   * the terms of any one of the MPL, the GPL or the LGPL.
   *
   * ***** END LICENSE BLOCK ***** */
  
  #ifndef _GUAC_HASH_H
  #define _GUAC_HASH_H
  
  #include <cairo/cairo.h>
  
  /**
   * Provides functions and structures for producing likely-to-be-unique hash
   * values for images.
   *
   * @file hash.h
   */
  
  /**
   * Produces a 24-bit hash value from all pixels of the given surface. The
   * surface provided must be RGB or ARGB with each pixel stored in 32 bits.
   * The hashing algorithm used is a variant of the cyclic polynomial rolling
   * hash.
   *
   * @param surface The Cairo surface to hash.
   * @return An arbitrary 24-bit unsigned integer value intended to be well
   *         distributed across different images.
   */
  unsigned int guac_hash_surface(cairo_surface_t* surface);
  
  /**
   * Given two Cairo surfaces, returns zero if the data contained within each
   * is identical, and a positive or negative value if the value of the first
   * is found to be lexically greater or less than the second respectively.
   *
   * @param a The first Cairo surface to compare.
   * @param b The Cairo surface to compare the first surface against.
   * @return Zero if the data contained within each is identical, and a positive
   *         or negative value if the value of the first is found to be lexically
   *         greater or less than the second respectively.
   */
  int guac_surface_cmp(cairo_surface_t* a, cairo_surface_t* b);
  
  #endif
  
  