Wanted: 128 bit integers

[Paul D. Anderson]

I'm working on a decimal arithmetic project and I need 128 bit 
integers in order to implement the decimal128 type. (The decimal 
value is stored in 128 bits; the coefficient field is 114 bits, 
to hold values with 34 decimal digits.)

I could use BigInt (but that's overkill) or I could code them up 
myself, which I'm willing to do if no alternative exists. But 
surely someone has already created this type, either as part of a 
larger project or as some kind of test problem, etc. Or perhaps 
someone would like to tackle it as a project of their own.

I specifically need unsigned 128 bit integers, but both signed 
and unsigned versions would probably have more general 
applications. Better yet, if it checked for overflow, like 
Andrei's CheckedInt class in TDPL, it would be more immediately 
useful.

This could also be the basis for a general fixed-size integer 
type, where the size is specified: CheckedInt!128, CheckedInt!96, 
etc. I recall having seen something like this mentioned in this 
forum.

So has anyone already done this? Does anyone want to take it on?

Thanks,

Paul