Re: Not good for Ada endorsement

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 2021-07-15 18:29, Lucretia wrote:
> On Thursday, 15 July 2021 at 16:56:40 UTC+1, Jeffrey R. Carter wrote:
>> On 7/15/21 5:13 PM, Lucretia wrote:
>>>
>>> I managed to get just under 4000 passes with a 1 bit array, but not using Ada's packed array. That's actually the slowest method, strangely.
>> So you have an array of a modular type, calculate an index and bit within it,
>> mask out that bit, and compare it to zero? I would have thought an unpacked
>> array of Boolean would be fastest.
> 
> Doesn't seem to be.

Unlikely unless compiled into machine-specific instructions. You should 
inspect the code.

> Also, the guy is using the packed bit as the final test of all the languages.
> 
>> A packed array of Boolean requires all the operations above, plus shifting the
>> bit to the LSB and treating the result as a Boolean, so it may not be that
> 
> Don't need to shift to the LSB, only need to shift the 1 to the bit location you want to test, invert and then check against 0.

Usually masks are either tabulated in a look-up table or are constants 
in a case choice.

>> surprising that it's slower.
> 
> I know. I  would've thought the compiler would've handled the packed array as a special case and optimised as much as possible there.

It is still unlikely to be faster than all arrays. You should probably 
try to use different element types and inspect the code.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de