Question

I’m converting a Guid to a BigInteger so I can base62 encode it. This works well, however, I can get negative numbers in BigInterger. How do I shift the BigInteger so the number is positive. I’ll also need to be able to shift it back so I can convert back to a Guid.

// GUID is a 128-bit signed integer 
Guid original = new Guid("{35db5c21-2d98-4456-88a0-af263ed87bc2}");
BigInteger b = new BigInteger(original.ToByteArray());

// shift so its a postive number?

Answer 1

Note: For url-safe version of Base64 consider using modifyed set of characters for Base64 ( http://en.wikipedia.org/wiki/Base64#URL_applications) instead of custom Base62.

I believe you can append 0 to the array first (will make higest byte always not to contain 1 in the highest bit) and then convert to BigInteger if you really need positive BigInteger.