IdentityHashMap & natStackTrace

[Bryce McKinlay]

Ranjit Mathew wrote:

>As Chris points, due to operator precedence weirdness this
>becomes a left shift by 3 or multiplication by 23, in line
>with what you observed.
>
>This was introduced almost two years ago in a merge from
>Classpath:
>
>http://gcc.gnu.org/cgi-bin/cvsweb.cgi/gcc/libjava/java/util/IdentityHashMap.java.diff?r1=1.8&r2=1.9&only_with_tag=MAIN
>
>Relevant change:
>
>  // This isn't necessarily prime, but it is an odd number of key/value
>  // slots, which has a higher probability of fewer collisions.
>- table = new Object[old.length * 2 + 2];
>+ table = new Object[old.length << 1 + 2];
>  
>

I'd like to make a plea to Classpath developers not to make this kind of 
change in the future. Not only does the new code introduce a bug, it is 
also more difficult to read, and it won't make any performance 
difference on any modern compiler. Its trivial for optimizers to 
substitute constant multiply's to left-shift operations, so please let 
the compiler take care of it!

Regards

Bryce