cryptopals/set1/utils.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include "utils.h"

const double eng_freq[] = {0.08167,0.01492,0.02782,0.04253,0.12702,0.02228,0.02015,0.06094,0.06966,0.00153,0.00772,0.04025,0.02406,0.06749,0.07507,0.01929,0.00095,0.05987,0.06327,0.09056,0.02758,0.00978,0.02360,0.00150,0.01974,0.00074,0};

int read_bytes(char *out_byte_array, int max_n) {
       char buf[2];
       int i = 0;
       while(((buf[0] = (char)getchar())!= EOF) && (buf[0] != '\n') && (i < max_n)) {
               buf[1] = getchar();
               if (buf[1] == EOF)
                       return -1;
               sscanf(buf, "%hhx", out_byte_array + i);
               i++;
       }
       // number of read characters
       return i;
}

int scan_bytes(char *out_byte_array, char *input, int max_n) {
       char c;
       int i = 0;

       while ((sscanf(input, "%2hhx", &c)!= EOF) && (i < max_n)) {
                out_byte_array[i] = c; 
                ++i;
                input += 2;
       }
       // number of read characters
       return i;
}

void print_bytes(char *byte_array, int n) {
    for (int i = 0; i < n; ++i) {
        printf("%02hhx", byte_array[i]);
    }
}

void freq(char *str, int n, double* freqs, char min, char max) {
       for (int i = 0; i < n; ++i) {
               if (str[i] >= min && str[i] <= max)
                    freqs[str[i] - min]++;
               else
                    freqs[max - min + 1]++;
       }
    
       for (int j = 0; j < max - min + 2; ++j)
            freqs[j] /= n;
}

double std(double *a, const double *b, int n) {
        double result = 0;
        for (int i = 0; i < n; ++i)
            result += (a[i] - b[i]) * (a[i] - b[i]); 
        result /= n;
        return result;
}

double freq_score(char *str, int n) {
        double score = 0;
        char* str_copy = (char*)malloc(n); 
        strncpy(str_copy, str, n);

        // last value is a frequency of non-alphaber symbols
        double* freqs = (double*)malloc(('z' - 'a' + 2) * sizeof(double));

        for (int i = 0; i < n; ++i)
            if (str_copy[i] >= 'A' && str_copy[i] <='Z')
                str_copy[i] = tolower(str[i]);  

        freq(str_copy, n, freqs, 'a', 'z');

        score = std(freqs, eng_freq, 'z' - 'a' + 2); 
        free(str_copy);
        free(freqs);
        return score;
}