Tag Archives: floating point

Exercises in Emulation: Xbox 360’s FMA Instruction

Years ago I worked in the Xbox 360 group at Microsoft. We were thinking about releasing a new console, and we thought it would be nice if that console could run the games of the previous console. Emulation is always … Continue reading

Posted in Floating Point | Tagged , , , , | 23 Comments

Sometimes Floating Point Math is Perfect

I’ve written in the past about how to compare floating-point numbers for the common scenario where two results should be similar but may not be identical. In that scenario it is reasonable to use an AlmostEqual function for comparisons. But … Continue reading

Posted in Floating Point | Tagged | 20 Comments

There are Only Four Billion Floats–So Test Them All!

A few months ago I saw a blog post touting fancy new SSE3 functions for implementing vector floor, ceil, and round functions. There was the inevitable proud proclaiming of impressive performance and correctness. However the ceil function gave the wrong … Continue reading

Posted in Floating Point | Tagged , | 44 Comments

Float Precision Revisited: Nine Digit Float Portability

Last year I pointed out that float variables can be converted to text and then back to the same binary value using printf(“%1.8e”). You can also use %.9g for more compact results. I also supplied a test program that used … Continue reading

Posted in Floating Point | Tagged , , , , | 18 Comments

Doubles are not floats, so don’t compare them

I’ve seen a few online discussions linking to my Comparing Floating Point Numbers page for misguided reasons and I wanted to discuss those reasons to help people understand why throwing epsilons at the problem without understanding the situation is a … Continue reading

Posted in Floating Point, Programming | Tagged , , , , | 25 Comments

That’s Not Normal–the Performance of Odd Floats

Denormals, NaNs, and infinities round out the set of standard floating-point values, and these important values can sometimes cause performance problems. The good news is, it’s getting better, and there are diagnostics you can use to watch for problems. In … Continue reading

Posted in AltDevBlogADay, Floating Point, Performance, Programming | Tagged , , , , , | 21 Comments

Exceptional Floating Point

Floating-point math has an answer for everything, but sometimes that’s not what you want. Sometimes instead of getting an answer to the question sqrt(-1.0) (it’s NaN) it’s better to know that your software is asking imaginary questions. The IEEE standard … Continue reading

Posted in AltDevBlogADay, Floating Point, Programming | Tagged , , , , | 29 Comments