RFR: 8236641: Improve Set.of(...).iterator() warmup characteristics

[Stuart Marks]

On 1/16/20 8:21 AM, Claes Redestad wrote:
> I've cleaned up a bit (SALT can be made into a long to reduce casts
> etc), and rolled it into the current patch:
> 
> http://cr.openjdk.java.net/~redestad/8236641/open.01/

OK, I think this makes sense. But I did have to stare at the code for a while to 
figure out what was going on. So, maybe a couple judicious comments would be 
helpful.

   68         SALT32L = (int)((color * seed) >> 16) & 0xFFFF_FFFFL; // avoid LSB 
and MSB

The comment "avoid LSB and MSB" isn't helping me here, and in fact it's 
confusing because I thought it applied to the "& 0xFFFF_FFFFL" part. Is there 
something else that ought to be said here, perhaps "select the middle 32 bits of 
the product"?

  770                 idx = (int) ((SALT32L * elements.length) >>> 32);
1063                 idx = (int) ((SALT32L * (table.length >> 1)) >>> 32) << 1;

These expressions replace floorMod(), which (at least to my brain) idiomatically 
ensures the return value is in the range [0..len-1]. It's not at all obvious 
what these do, although I think they do the same thing. Can we add a comment 
something like, "add a 'random' starting index based on the SALT"?

Thanks,

s'marks