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freq.c
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freq.c
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#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include "misc.h"
#include "charset.h"
#include "freq.h"
/* Initialize a struct freq. */
void freq_init(struct freq *f, const struct charset *charset) {
memset(f, 0, sizeof(*f));
f->charset = charset;
f->freq = malloc(sizeof(*f->freq) * charset->length);
if (f->freq == NULL)
system_error("malloc");
memset(f->freq, 0, sizeof(*f->freq) * charset->length);
}
/* Deinitialize a struct freq. */
void freq_fini(struct freq *f) {
free(f->freq);
memset(f, 0, sizeof(*f));
}
/*
* Compute the frequency of the string str with repect to the charset given in
* the initialization, but only take one character every n characters of str.
*/
void freq_compute_stride(struct freq *f, const char *str, size_t n) {
/* Use a temporary array "count" so that float errors won't disturb the
* result. */
size_t *count;
size_t i;
size_t total;
size_t nlen;
const struct charset *cs; /* shorthand */
cs = f->charset;
nlen = strlen(str);
count = malloc(sizeof(*count) * cs->length);
if (count == NULL)
system_error("malloc");
memset(count, 0, sizeof(*count) * cs->length);
for (i = 0; i < nlen; i += n) {
int o = cs_ord(cs, str[i]);
if (o == -1)
continue;
count[o]++;
}
total = 0;
for (i = 0; i < cs->length; i++)
total += count[i];
for (i = 0; i < cs->length; i++)
f->freq[i] = count[i] / (float)total;
free(count);
}
/*
* Compute the frequency of the string str with repect to the charset given in
* the initialization.
*/
void freq_compute(struct freq *f, const char *str) {
freq_compute_stride(f, str, 1);
}