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Last night I needed a square root function that would work on 64-bit unsigned integers. I have been using the standard library's *sqrt*, but my first thought was that an integer square root could be faster.

I looked around and found what was said to be a "fast" integer square root on Stack Overflow by Craig McQueen. I used the code as-is except that I changed it to use 64-bit unsigned ints because that was what I needed.

It seemed like a reasonably performance efficient algorithm, but I had always heard that sqrt, even in hardware, was slow. Because sqrt gets used a lot, I thought better safe than sorry, so this morning I decided to benchmark the integer algorithm against *sqrt* just to be sure.

- Int Elapsed 1506419us
- Float Elapsed 159330us
- Float+Cast Elapsed 182160us

It turns out that the hardware-based floating point

I'll keep the integer square root, but this post is going in the comments for it.

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Int Elapsed 571950us

Float Elapsed 38746us

Float + Cast Elapsed 56759us

Float is 14.76x faster, 10.08x with the static_cast.

Also, this was not the timing for one sqrt, but 4,000,000.

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Sqrt float: 12583.508ms

Sqrt double: 12371.292ms

Fast uint sqrt: 24388.667ms

Fast ulong sqrt: 96830.309ms

That's for 1e9 loops with adding all sqrts together to prevent optimizer from ignoring the values. Also did the same test in C# for fun:

Sqrt double: 13547ms

Fast uint sqrt: 25701ms

Fast ulong sqrt: 121126ms

Not much difference. :)

Homepage: omeg.pl email:

Homepage: www.onemanmmo.com email:one at onemanmmo dot com