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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define CTOI(c) ((c) - 'A')
#define ITOC(c) ((c) + 'A')
#define ALPHACHARS 26
void preprocess(char *str)
{
char *src = str, *dest = str;
while (*src != '\0') {
if (isalpha(*src))
*(dest++) = toupper(*src);
src++;
}
*dest = '\0';
}
double calc_ic_column(const char *text, size_t length, size_t offset, size_t spacing)
{
unsigned foundc[ALPHACHARS] = {0}, total_chars = 0;
unsigned long pre_sum = 0;
for (size_t i = offset; i < length; i += spacing, total_chars++)
foundc[CTOI(text[i])]++;
for (unsigned i = 0; i < ALPHACHARS; i++)
pre_sum += foundc[i] * (foundc[i] - 1);
return (double)pre_sum / ((double)total_chars * (double)(total_chars - 1) / ALPHACHARS);
}
double calc_ic(const char *text, size_t length, size_t width)
{
double total = 0;
for (size_t offset = 0; offset < width; offset++)
total += calc_ic_column(text, length, offset, width);
return total / width;
}
int main(int argc, char **argv)
{
char *text;
size_t length;
unsigned long max;
if (argc != 3) {
fprintf(stderr, "Usage: %s <text> <max>\a\n", argv[0]);
exit(EXIT_FAILURE);
}
text = argv[1];
max = strtoul(argv[2], NULL, 10);
preprocess(text);
length = strlen(text);
for (unsigned long spacing = 1; spacing <= max; spacing++) {
double ic = calc_ic(text, length, spacing);
unsigned barlen;
if (ic > 0.8 && ic < 4)
barlen = (ic - 0.8) / 3.2 * 40.0;
else
barlen = ic <= 0.8 ? 0 : 40;
printf("%3lu - %6.3f ", spacing, ic);
for (unsigned i = 0; i < barlen; i++)
putchar('#');
putchar('\n');
}
return EXIT_SUCCESS;
}
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