Integer cube root

Question

I\'m looking for fast code for 64-bit (unsigned) cube roots. (I\'m using C and compiling with gcc, but I imagine most of the work required will be language- and compiler-agnost

Answer 1

The book "Hacker's Delight" has algorithms for this and many other problems. The code is online here. EDIT: That code doesn't work properly with 64-bit ints, and the instructions in the book on how to fix it for 64-bit are somewhat confusing. A proper 64-bit implementation (including test case) is online here.

I doubt that your squareroot function works "correctly" - it should be ulong a for the argument, not n :) (but the same approach would work using cbrt instead of sqrt, although not all C math libraries have cube root functions).