Added hash.c and hash.h, including a basic image hash function.

This commit is contained in:
Michael Jumper 2012-08-19 20:46:02 -07:00
parent e02b3e3a0e
commit 97ac78c1e5
3 changed files with 172 additions and 0 deletions

57
libguac/include/hash.h Normal file
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@ -0,0 +1,57 @@
/* ***** 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>
/**
* 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.
*/
int guac_hash_surface(cairo_surface_t* surface);
#endif

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@ -42,6 +42,7 @@ libguacincdir = $(includedir)/guacamole
libguacinc_HEADERS = \
../include/client.h \
../include/error.h \
../include/hash.h \
../include/instruction.h \
../include/layer.h \
../include/plugin.h \
@ -60,6 +61,7 @@ libguac_la_SOURCES = \
client.c \
client-handlers.c \
error.c \
hash.c \
instruction.c \
palette.c \
plugin.c \

113
libguac/src/hash.c Normal file
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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>
#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.
*/
int _guac_hash_32to24(int value) {
/* Grab highest-order byte */
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));
}
int guac_hash_surface(cairo_surface_t* surface) {
/* Init to zero */
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 */
int color = *row;
row++;
/* Compute next hash */
hash_value =
_guac_rotate(hash_value, 1) ^ _guac_hash_32to24(color);
}
} /* end for each row */
/* Done */
return hash_value;
}