On Jun 15, 2011, at 5:48 PM, Christian Thalinger wrote:
> On Jun 15, 2011, at 5:26 PM, Rémi Forax wrote:
>> I've just finished to code a sample for the cookbook that does
>> integer operation (+ and -) with overflow (to BigInteger).
>>
>> https://code.google.com/p/jsr292-cookbook/source/browse/#svn%2Ftrunk%2Fbinary-operation%2Fsrc%2Fjsr292%2Fcookbook%2Fbinop
>
> How do I build this thing? -- Christian
Got it. I thought there is probably something like a build.xml.
Investigating...
-- Christian
>
>>
>> For a code like this one:
>> max = ...
>> for(i=0; i<max; i = i + 1) {
>> // do nothing
>> }
>>
>> i + 1 is transformed to:
>>
>> if (i.getClass() == Integer.class) {
>> int j = i.intValue();
>> if (j != MAXINT) {
>> i = Integer.valueOf(j + 1);
>> } else {
>> fallback();
>> }
>> } else {
>> fallback();
>> }
>>
>> but there is a bad news, perf of i + 1 considering 1 as a constant
>> are *worst* (2 or 3 times !!) that using the double xor trick.
>>
>> // with the optimization
>> [forax@localhost binary-operation]$ time java -cp .:classes PerfOpt
>> real 0m0.954s
>> user 0m1.030s
>> sys 0m0.087s
>>
>> // without
>> [forax@localhost binary-operation]$ time java -cp .:classes Perf
>> real 0m0.378s
>> user 0m0.407s
>> sys 0m0.081s
>>
>> Knowing that the double xor trick does 4 comparisons and
>> the constant trick only two, the problem comes from either
>> my code or the way the VM inlines the method handles.
>>
>> I've found no problem in my code so ... :)
>> Playing with the VM logs, the method containing (j != MAXINT) is not inlined
>> because it hits the maximum depth (as far as I remember this problem
>> is new, the older algorithm, the one that didn't propagate MDO, didn't
>> exhibit this problem).
>> Moreover, the VM tries to inline some parts of the fallback method
>> (twice :( )
>> even if this code never called.
>>
>> The way the VM decides to inline method handles in this case is not good
>> at all.
>>
>> Rémi
>>
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>
>
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