114 lines
3.3 KiB
C
114 lines
3.3 KiB
C
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/* ***** BEGIN LICENSE BLOCK *****
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* Version: MPL 1.1/GPL 2.0/LGPL 2.1
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*
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* The contents of this file are subject to the Mozilla Public License Version
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* 1.1 (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.mozilla.org/MPL/
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*
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* Software distributed under the License is distributed on an "AS IS" basis,
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* WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
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* for the specific language governing rights and limitations under the
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* License.
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*
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* The Original Code is libguac.
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*
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* The Initial Developer of the Original Code is
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* Michael Jumper.
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* Portions created by the Initial Developer are Copyright (C) 2010
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* the Initial Developer. All Rights Reserved.
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*
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* Contributor(s):
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*
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* Alternatively, the contents of this file may be used under the terms of
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* either the GNU General Public License Version 2 or later (the "GPL"), or
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* the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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* in which case the provisions of the GPL or the LGPL are applicable instead
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* of those above. If you wish to allow use of your version of this file only
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* under the terms of either the GPL or the LGPL, and not to allow others to
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* use your version of this file under the terms of the MPL, indicate your
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* decision by deleting the provisions above and replace them with the notice
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* and other provisions required by the GPL or the LGPL. If you do not delete
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* the provisions above, a recipient may use your version of this file under
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* the terms of any one of the MPL, the GPL or the LGPL.
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*
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* ***** END LICENSE BLOCK ***** */
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#include <stdint.h>
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#include <cairo/cairo.h>
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/*
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* Arbitrary hash function whhich maps ALL 32-bit numbers onto 24-bit numbers
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* evenly, while guaranteeing that all 24-bit numbers are mapped onto
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* themselves.
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*/
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int _guac_hash_32to24(int value) {
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/* Grab highest-order byte */
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int upper = value & 0xFF000000;
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/* XOR upper with lower three bytes, truncate to 24-bit */
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return
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(value & 0xFFFFFF)
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^ (upper >> 8)
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^ (upper >> 16)
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^ (upper >> 24);
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}
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/**
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* Rotates a given 32-bit integer by N bits.
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*
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* NOTE: We probably should check for available bitops.h macros first.
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*/
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unsigned int _guac_rotate(unsigned int value, int amount) {
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/* amount = amount % 32 */
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amount &= 0x1F;
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/* Return rotated amount */
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return (value >> amount) | (value << (32 - amount));
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}
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int guac_hash_surface(cairo_surface_t* surface) {
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/* Init to zero */
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int hash_value = 0;
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int x, y;
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/* Get image data and metrics */
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unsigned char* data = cairo_image_surface_get_data(surface);
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int width = cairo_image_surface_get_width(surface);
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int height = cairo_image_surface_get_height(surface);
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int stride = cairo_image_surface_get_stride(surface);
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for (y=0; y<height; y++) {
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/* Get current row */
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uint32_t* row = (uint32_t*) data;
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data += stride;
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for (x=0; x<width; x++) {
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/* Get color at current pixel */
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int color = *row;
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row++;
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/* Compute next hash */
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hash_value =
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_guac_rotate(hash_value, 1) ^ _guac_hash_32to24(color);
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}
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} /* end for each row */
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/* Done */
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return hash_value;
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}
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