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Add function to decode base64

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This commit is contained in:
Dimitri Lozeve 2020-06-04 20:11:00 +02:00
parent b1c777d1ea
commit f3a8d9c74f
3 changed files with 62 additions and 3 deletions
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42
utils.c
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@ -36,10 +36,10 @@ size_t hex_to_bytes(unsigned char *out, const char hex[static 1]) {
return strlen(hex) / 2 + strlen(hex) % 2;
}
char *bytes_to_base64(char *out, const unsigned char in[static 1], size_t len) {
static const char base64_table[65] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
static const char base64_table[65] =
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
char *bytes_to_base64(char *out, const unsigned char in[static 1], size_t len) {
for (size_t i = 0; i < len - 2; i += 3) {
size_t j = i / 3 * 4;
out[j] = base64_table[in[i] >> 2];
@ -50,6 +50,42 @@ char *bytes_to_base64(char *out, const unsigned char in[static 1], size_t len) {
return out;
}
size_t base64_to_bytes(unsigned char *out, const char *in) {
char decoding_table[256] = {0};
for (size_t i = 0; i < 64; ++i) {
decoding_table[(unsigned char)base64_table[i]] = i;
}
size_t in_length = strlen(in);
if (in_length % 4 != 0) {
return 0;
}
size_t i = 0;
for (size_t j = 0; j < in_length - 3;) {
unsigned char sextet1 =
in[j] == '=' ? 0 : decoding_table[(unsigned char)in[j]];
unsigned char sextet2 =
in[j + 1] == '=' ? 0 : decoding_table[(unsigned char)in[j + 1]];
unsigned char sextet3 =
in[j + 2] == '=' ? 0 : decoding_table[(unsigned char)in[j + 2]];
unsigned char sextet4 =
in[j + 3] == '=' ? 0 : decoding_table[(unsigned char)in[j + 3]];
out[i] = sextet1 << 2;
out[i] += sextet2 >> 4;
out[i + 1] = sextet2 << 4;
out[i + 1] += sextet3 >> 2;
out[i + 2] = sextet3 << 6;
out[i + 2] += sextet4;
j += 4;
i += 3;
}
return i;
}
double frequency_score(const char *buf, size_t len) {
static const double english_freqs[27] = {
0.08167, 0.01492, 0.02782, 0.04253, 0.12702, 0.02228, 0.02015, // A-G