62 lines
1.8 KiB
C
62 lines
1.8 KiB
C
#include "utils.h"
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#include <ctype.h>
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#include <math.h>
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#include <string.h>
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unsigned char hex_to_byte(const char c) {
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if (isdigit(c)) {
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return c - '0';
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}
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return 10 + c - 'a';
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}
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size_t hex_to_bytes(unsigned char *out, const char hex[static 1]) {
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for (size_t i = 0; i < strlen(hex); ++i) {
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char c = tolower(hex[i]);
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unsigned char value = hex_to_byte(c);
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if (i % 2 == 0) {
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value <<= 4;
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}
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out[i / 2] += value;
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}
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return strlen(hex) / 2 + strlen(hex) % 2;
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}
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unsigned char *bytes_to_base64(unsigned char *out,
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const unsigned char in[static 1], size_t len) {
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static const unsigned char base64_table[65] =
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"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
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for (size_t i = 0; i < len - 2; i += 3) {
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size_t j = i / 3 * 4;
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out[j] = base64_table[in[i] >> 2];
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out[j + 1] = base64_table[((in[i] & 0x03) << 4) | (in[i + 1] >> 4)];
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out[j + 2] = base64_table[((in[i + 1] & 0x0f) << 2) | (in[i + 2] >> 6)];
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out[j + 3] = base64_table[in[i + 2] & 0x3f];
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}
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return out;
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}
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double frequency_score(unsigned char *buf, size_t len) {
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static const double english_freqs[26] = {
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0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, // A-G
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0.06094, 0.06966, 0.00153, 0.00772, 0.04025, 0.02406, 0.06749, // H-N
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0.07507, 0.01929, 0.00095, 0.05987, 0.06327, 0.09056, 0.02758, // O-U
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0.00978, 0.02360, 0.00150, 0.01974, 0.00074 // V-Z
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};
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unsigned int counts[26] = {0};
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for (size_t i = 0; i < len; ++i) {
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unsigned char c = tolower(buf[i]) - 'a';
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if (c < 26) {
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counts[c]++;
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}
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}
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double chi2 = 0;
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for (size_t i = 0; i < 26; ++i) {
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double expected = len * english_freqs[i];
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chi2 += pow(counts[i] - expected, 2) / expected;
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}
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return chi2;
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}
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