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static char encoding_table[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X',
'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
'w', 'x', 'y', 'z', '0', '1', '2', '3',
'4', '5', '6', '7', '8', '9', '+', '/'};
static char *decoding_table = NULL;
static int mod_table[] = {0, 2, 1};
static void build_decoding_table()
{
decoding_table = malloc(256);
for (int i = 0; i < 0x40; i++)
{
decoding_table[encoding_table[i]] = i;
}
}
static char *base64_encode(const char *data, size_t *output_length)
{
size_t input_length = strlen(data);
*output_length = (size_t) (4.0 * ceil((double) input_length / 3.0));
char *encoded_data = malloc(*output_length);
if (encoded_data == NULL)
{
return NULL;
}
for (int i = 0, j = 0; i < input_length;)
{
uint32_t octet_a = i < input_length ? data[i++] : 0;
uint32_t octet_b = i < input_length ? data[i++] : 0;
uint32_t octet_c = i < input_length ? data[i++] : 0;
uint32_t triple = (octet_a << 0x10) + (octet_b << 0x08) + octet_c;
encoded_data[j++] = encoding_table[(triple >> 3 * 6) & 0x3F];
encoded_data[j++] = encoding_table[(triple >> 2 * 6) & 0x3F];
encoded_data[j++] = encoding_table[(triple >> 1 * 6) & 0x3F];
encoded_data[j++] = encoding_table[(triple >> 0 * 6) & 0x3F];
}
for (int i = 0; i < mod_table[input_length % 3]; i++)
{
encoded_data[*output_length - 1 - i] = '=';
}
return encoded_data;
}
static char *base64_decode(const char *data, size_t *output_length)
{
size_t input_length = strlen(data);
if (decoding_table == NULL)
{
build_decoding_table();
}
if (input_length % 4 != 0)
{
return NULL;
}
*output_length = input_length / 4 * 3;
if (data[input_length - 1] == '=')
{
(*output_length)--;
}
if (data[input_length - 2] == '=')
{
(*output_length)--;
}
char *decoded_data = malloc(*output_length);
if (decoded_data == NULL)
{
return NULL;
}
for (int i = 0, j = 0; i < input_length;)
{
uint32_t sextet_a = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
uint32_t sextet_b = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
uint32_t sextet_c = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
uint32_t sextet_d = data[i] == '=' ? 0 & i++ : decoding_table[data[i++]];
uint32_t triple = (sextet_a << 3 * 6) + (sextet_b << 2 * 6) + (sextet_c << 1 * 6) + (sextet_d << 0 * 6);
if (j < *output_length)
{
decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
}
}
return decoded_data;
} |
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