int (char c) { if (c >= 'A' && c <= 'Z') return c - 65; if (c >= 'a' && c <= 'z') return (c - 97) + 26; if (c >= '0' && c <= '9') return (c - 48) + 52; if (c == '+') return 62; if (c == '/') return 63; return c != '=' ? -1 : 0; }