Counting bits in a ulong

[ttk]

On Saturday, 6 June 2020 at 04:19:44 UTC, sebasg wrote:
> On Friday, 5 June 2020 at 19:12:43 UTC, ttk wrote:
>> Source is here .. a bit large, since I manually unrolled loops 
>> 100x to minimize the impact of looping logic (particularly the 
>> now() call):
>>
>> http://ciar.org/h/popcount.d
>
> Jesus. Shouldn't you be able to generate that instead of
> copy-pasting? It's D, after all.

A fair point.  Duplicating it in emacs was literally five 
keystrokes, but I should rewrite it to use templates anyway (more 
excuse to fiddle with D!).

Also, I figured out why the 16-bit lookup wasn't more closely 
2.0x the performance of the 8-bit lookup.  The L1 cache is 192KB, 
but that's divided across its six cores, so this single-threaded 
program only got 32KB of L1 to play with.  The 8-bit lookup table 
fit in that, but only half of the 16-bit lookup table did.