Counting bits in a ulong
ttk
ttk at ciar.org
Mon Jun 8 18:08:55 UTC 2020
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.
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