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

libguac/include/hash.h

@@ -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
+

libguac/src/Makefile.am

@@ -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          \

libguac/src/hash.c

@@ -0,0 +1,113 @@
+
+/* ***** 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;
+
+}
+