Problem - Kevin Tafuro

}
break;
default:
if (isspace(p[0])) p++;
else {
*l = ERR_NOT_HEX;
free(ret);
return 0;
}
}
if ((shift = (shift + 4) % 8) != 0) {
*r++ = value;
value = 0;
}
}
if (!shift) {
*l = ERR_BAD_SIZE;
free(ret);
return 0;
}
*l = (r - ret);
return (unsigned char *)realloc(ret, *l);
}
4.5 Performing Base64 Encoding
Problem
You want to represent binary data in as compact a textual representation as is reasonable,
but the data must be easy to encode and decode, and it must use printable
text characters.
Solution
Base64 encoding encodes six bits of data at a time, meaning that every six bits of
input map to one character of output. The characters in the output will be a numeric
digit, a letter (uppercase or lowercase), a forward slash, a plus, or the equal sign
(which is a special padding character).
Note that four output characters map exactly to three input characters. As a result, if
the input string isn’t a multiple of three characters, you’ll need to do some padding
(explained in the “Discussion” section).
Discussion
The base64 alphabet takes 6-bit binary values representing numbers from 0 to 63
and maps them to a set of printable ASCII characters. The values 0 through 25 map
to the uppercase letters in order. The values 26 through 51 map to the lowercase letters.
Then come the decimal digits from 0 to 9, and finally + and /.
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Performing Base64 Encoding | 123