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#ifndef UTILS_H
#define UTILS_H 1
#include <math.h>
#include <stdlib.h>
#include <unistd.h>
#define MAXLEN 961 // maximum string length
static inline size_t makehist(unsigned char const * const buf, ssize_t * const hist, size_t len) {
ssize_t wherechar[256];
size_t i, histlen;
histlen = 0;
for (i = 0; i < 256; i++)
wherechar[i] = -1;
for (i = 0; i < len; i++) {
if (wherechar[buf[i]] == -1) {
wherechar[(int)buf[i]] = histlen;
histlen++;
}
hist[wherechar[(int)buf[i]]]++;
}
return histlen;
}
static inline double entropy(ssize_t * const hist, size_t histlen, size_t len) {
size_t i;
double H;
H = 0.0;
for (i = 0; i < histlen; i++) {
H -= (double)hist[i] / len * log2((double)hist[i] / len);
}
return H;
}
static inline double entropy_from_buffer(unsigned char const * const buffer, size_t size)
{
ssize_t * const hist_array = malloc(size * sizeof(*hist_array));
if (!hist_array) {
return -1.0;
}
size_t hist_length = makehist(buffer, hist_array, size);
double entr = entropy(hist_array, hist_length, size);
free(hist_array);
return entr;
}
#endif
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