String.lastIndexOf confused by unpaired trailing surrogate

[Ulf Zibis]

Am 24.03.2010 08:32, schrieb Martin Buchholz:
> Hi Ulf,
>
> You have this interesting optimization:
>
>       public static boolean isSurrogate(char ch) {
> -        return ch>= MIN_SURROGATE&&  ch<  MAX_SURROGATE + 1;
> +        return (ch -= MIN_SURROGATE)>= 0&&  ch<  MAX_SURROGATE + 1 -
> MIN_SURROGATE;
>       }
>
> Do you have any evidence that hotspot can produce better code from this,
> or that there is a measurable performance improvement?
> Or was this just an experiment?
>    

If isHighSurrogate and isSurrogate are used consecutive on same char, 
result of ch -= MIN_SURROGATE could be used for both.
If isLowSurrogate and isSurrogate are used consecutive on same char, 
result of ch -= MAX_SURROGATE would fit better.
If isHighSurrogate and isLowSurrogate are used consecutive on same char, 
result of ch -= MIN_LOW_SURROGATE would fit better.

I suggest using 1st pair in JDK library.

-Ulf