Unsigned 128-bit division on 64-bit machine

64-bit division integer-division 128-bit
rookie picture rookie · Dec 8, 2009 · Viewed 7k times · Source

I have a 128-bit number stored as 2 64-bit numbers ("Hi" and "Lo"). I need only to divide it by a 32-bit number. How could I do it, using the native 64-bit operations from CPU?

(Please, note that I DO NOT need an arbitrary precision library. Just need to know how to make this simple division using native operations. Thank you).

Answer

F.D.Castel picture F.D.Castel · Dec 10, 2009

If you are storing the value (128-bits) using the largest possible native representation your architecture can handle (64-bits) you will have problems handling the intermediate results of the division (as you already found :) ).

But you always can use a SMALLER representation. What about FOUR numbers of 32-bits? This way you could use the native 64-bits operations without overflow problems.

A simple implementation (in Delphi) can be found here.

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