StrictMath performance improvement not ported to Math?

Martin Desruisseaux martin.desruisseaux at
Tue Nov 22 21:47:13 UTC 2011

Hello Joe

Le 22/11/11 04:20, Joe Darcy a écrit :
>> 3) In if statements, replaced:
>> (a == 0.0d) && (Double.doubleToLongBits(a) == negativeZeroDoubleBits)
>> by
>> (Double.doubleToLongBits(a) == negativeZeroDoubleBits)
>> since the later implies the former.
> The performance properties of the two versions of the code may differ 
> depending on the frequency of zeros in the input and the cost of the bitwise 
> conversion operation. I'd prefer to leave the code logic as-is in absence of 
> some benchmarking that showed a helpful difference.
I presumed that Double.doubleToRawLongBits(a) - I forgot the "Raw" in my 
previous post - was very cheap after HotSpot intrinsics (which exist according 
vmSymbols.hpp). If my old memory from 80286 assembler still have some value, it 
would have simply be a matter of comparing the value from the same memory 
address using a different machine instruction. But obviously this is only 
supposition, today picture is very different and I have no benchmark for 
confirming or refuting my supposition…

> I'd prefer to see a webrev with:
> * All min/max logic from StrictMath moved into math, including for the 
> integral types int and long
> * All StrictMath min/max methods delegating to their Math counterpart
Done. I updated the webrev at the same URL:
The new Math code is a verbatim copy-and-paste from StrictMath, including the 

I also made StrictMath.abs methods delegating to their Math counterpart, after 
making sure that the code was really identical. After this change, the only 
remaining duplicated code is toDegrees and toRadians. For those two methods, I 
added a comment saying why StrictMath dos not delegate to Math for them (because 
the StrictMath methods have the "strictfp" modifier - but this modifier is easy 
to miss, so a comment may be a worthy safety).

> * Verification all java/lang/Math and java/lang/StrictMath regression tests 
> still pass
I quicky tried, but it seems to be a bit tricky for me since I'm on a MacOS 
machine. Maybe it will be easier when the MacOS port project will be completed...


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