g_base64.c

#include "g_local.h"

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};


char *base64_encode(const unsigned char *data, size_t ilen, size_t *olen) {
	int i, j;
    *olen = 4 * ((ilen + 2) / 3);

    char *encoded_data = malloc(*olen);
    if (encoded_data == NULL) {
		return NULL;
	}

    for (i = 0, j = 0; i < ilen;) {

        uint32_t octet_a = i < ilen ? (unsigned char)data[i++] : 0;
        uint32_t octet_b = i < ilen ? (unsigned char)data[i++] : 0;
        uint32_t octet_c = i < ilen ? (unsigned char)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 (i = 0; i < mod_table[ilen % 3]; i++) {
        encoded_data[*olen - 1 - i] = '=';
	}

    return encoded_data;
}


unsigned char *base64_decode(const char *data, size_t ilen, size_t *olen) {
	int i, j;
	
    if (decoding_table == NULL) {
		decoding_table = malloc(256);

		for (i=0; i<64; i++) {
			decoding_table[(unsigned char) encoding_table[i]] = i;
		}
	}

    if (ilen % 4 != 0) {
		return NULL;
	}

    *olen = ilen / 4 * 3;
    if (data[ilen - 1] == '=') (*olen)--;
    if (data[ilen - 2] == '=') (*olen)--;

    unsigned char *decoded_data = malloc(*olen);
    if (decoded_data == NULL) {
		return NULL;
	}

    for (i=0, j=0; i<ilen;) {
        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 < *olen) decoded_data[j++] = (triple >> 2 * 8) & 0xFF;
        if (j < *olen) decoded_data[j++] = (triple >> 1 * 8) & 0xFF;
        if (j < *olen) decoded_data[j++] = (triple >> 0 * 8) & 0xFF;
    }

	free(decoding_table);
	
    return decoded_data;
}