Base64 加密算法（Author 蒋柏良 Jerry Jiang)

代码说明：

Base64 加密算法（Author 蒋柏良 Jerry Jiang)-* * DESCRIPTION * Base64 processes input in 24bit chunks by converting each chunk into 4 * bytes of output. It does so by splitting input into four 6bit groups and * using these as indexes in the following substitution table- * const char base64_map[] = * "ABCDEFGHIJKLMNOPQRSTUVWXYZ" * "abcdefghijklmnopqrstuvwxyz" * "0123456789+/" * If an input is not a multiple of 3 bytes, it s padded with zeros. In * this case the output bytes that consist entirely of the pad data are * replaced with = . * * Example * An input of 0x00 0x45 0xF2 is equivalent to 00000000 01000101 11110010 * bit sequence, which s then split into 000000 000100 010111 110010 * and these are substituted to produce the following base64 encoding * A E X y * * RETURN VALUE * b64_length() should return output length for the input of len bytes. * b64_encode() should encode len bytes from src int