On 10/13/2011 09:55 AM, Ulf Zibis wrote:
Am 11.10.2011 19:49, schrieb Xueming Shen:
I don't know which one is better, I did a run on
private static boolean op1(int b) {
return (b >> 6) != -2;
}
private static boolean op2(int b) {
return (b & 0xc0) != 0x80;
}
private static boolean op3(byte b) {
return b >= (byte)0xc0;
}
with 1000000 iteration on my linux machine, and got the scores
op1=1149
op2=1147
op3=1146
I would interpret it as they are identical.
Me too. thanks for your effort.
Maybe the comparison would differ on different architectures.
So I would prefer opt3, because the others ...
1. in question need 1 more CPU register to save the original value of
b for later usage
2. need 1 more constant to load into CPU
and opt 3 ...
3. is the best readable source code
4. in question seems best to help Hotspot finding best optimization on
arbitrary architectures.
I doubt it's more "readable":-), given it's the "byte operation" means
"<0x80 && >= 0xc0" in int. You need "b" to be byte for b >= (byte)0xc0
to be the equivalent of "<0x80 && >= 0xc0" and all use cases in UTF-8
existing implementation the "b" has been stored in "int" already. Arguably
you can update the whole implementation to achieve this, but personally
I would like to just stick to the problem this proposal is trying to solve.
And, no, for the same reason I don't want to replace all "(b & 0xc0) != 0x80
by "isNotContinuation(b)", they just look fine for me, together with their
neighbors, such as "<0x80 && >= 0xc0".
-Sherman
Additionally I guess using always byte variables would in question
help HotSpot to optimize with 1-byte-operand CPU instructions.
Don't you like to replace all "(bx & 0xc0) != 0x80" by
"isNotContinuation(bx)" ?
-Ulf
