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

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/*
* Copyright (C) 2013 Glyptodon LLC
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
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#include "config.h"
#include <stdint.h>
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#include <string.h>
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#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;
}