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.
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
