guacamole-spice-protocol/src/libguac/hash.c

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/* ***** 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 ***** */
#include <stdint.h>
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#include <string.h>
#include <cairo/cairo.h>
/*
* Arbitrary hash function whhich maps ALL 32-bit numbers onto 24-bit numbers
* evenly, while guaranteeing that all 24-bit numbers are mapped onto
* themselves.
*/
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unsigned int _guac_hash_32to24(unsigned int value) {
/* Grab highest-order byte */
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unsigned int upper = value & 0xFF000000;
/* XOR upper with lower three bytes, truncate to 24-bit */
return
(value & 0xFFFFFF)
^ (upper >> 8)
^ (upper >> 16)
^ (upper >> 24);
}
/**
* Rotates a given 32-bit integer by N bits.
*
* NOTE: We probably should check for available bitops.h macros first.
*/
unsigned int _guac_rotate(unsigned int value, int amount) {
/* amount = amount % 32 */
amount &= 0x1F;
/* Return rotated amount */
return (value >> amount) | (value << (32 - amount));
}
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unsigned int guac_hash_surface(cairo_surface_t* surface) {
/* Init to zero */
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unsigned int hash_value = 0;
int x, y;
/* Get image data and metrics */
unsigned char* data = cairo_image_surface_get_data(surface);
int width = cairo_image_surface_get_width(surface);
int height = cairo_image_surface_get_height(surface);
int stride = cairo_image_surface_get_stride(surface);
for (y=0; y<height; y++) {
/* Get current row */
uint32_t* row = (uint32_t*) data;
data += stride;
for (x=0; x<width; x++) {
/* Get color at current pixel */
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unsigned int color = *row;
row++;
/* Compute next hash */
hash_value =
_guac_rotate(hash_value, 1) ^ color ^ 0x1B872E69;
}
} /* end for each row */
/* Done */
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return _guac_hash_32to24(hash_value);
}
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int guac_surface_cmp(cairo_surface_t* a, cairo_surface_t* b) {
/* Surface A metrics */
unsigned char* data_a = cairo_image_surface_get_data(a);
int width_a = cairo_image_surface_get_width(a);
int height_a = cairo_image_surface_get_height(a);
int stride_a = cairo_image_surface_get_stride(a);
/* Surface B metrics */
unsigned char* data_b = cairo_image_surface_get_data(b);
int width_b = cairo_image_surface_get_width(b);
int height_b = cairo_image_surface_get_height(b);
int stride_b = cairo_image_surface_get_stride(b);
int y;
/* If core dimensions differ, just compare those. Done. */
if (width_a != width_b) return width_a - width_b;
if (height_a != height_b) return height_a - height_b;
for (y=0; y<height_a; y++) {
/* Compare row. If different, use that result. */
int cmp_result = memcmp(data_a, data_b, width_a * 4);
if (cmp_result != 0)
return cmp_result;
/* Next row */
data_a += stride_a;
data_b += stride_b;
}
/* Otherwise, same. */
return 0;
}