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/*
* This code was done
* by an anonymous gnome
* ------------------------
* That's pure mathematics, so no sense to adding license shit here.
*/
#include <stdlib.h>
#include <math.h>
#include "r_types.h"
static double get_px(ut8 x, const ut8 *data, ut64 size) {
ut64 i, count = 0;
for (i = 0; i < size; i++)
if (data[i] == x)
count++;
return (double) count / size;
}
R_API double r_hash_entropy(const ut8 *data, ut64 size) {
ut32 x;
double h = 0, px, log2 = log (2.0);
for (x = 0; x < 256; x++) {
px = get_px (x, data, size);
if (px > 0)
h += -px * (log (px) / log2);
}
return h;
}
R_API double r_hash_entropy_fraction(const ut8 *data, ut64 size) {
double h = r_hash_entropy (data, size);
if (size < 256)
return h * log (2.0) / log (size);
return h/8; //(size/256);//8;
}
// 0-8
#if TEST
main() {
int i;
ut8 b[40960];
for (i=0;i<sizeof(b);i++)
b[i] = i;
//memset (b, 'A', sizeof (b));
memset (b, 'A', 512);
printf ("%f\n", r_hash_entropy (b, 10));
printf ("%f\n", r_hash_entropy (b, 100));
printf ("%f\n", r_hash_entropy (b, 200));
printf ("%f\n", r_hash_entropy (b, 256));
printf ("%f\n", r_hash_entropy (b, 4095));
printf ("%f\n", r_hash_entropy (b, 8095));
printf ("%f\n", r_hash_entropy (b, sizeof (b)));
}
#endif
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