[chbot] New chocolate fish challenge

Charles Manning cdhmanning at gmail.com
Wed Nov 19 03:55:10 GMT 2014


Some sort of pseudorandom number shift and xor would do this. These are
used to generate longish patterns from short registers.


This is how some things like GPS gold codes work.

On Wed, Nov 19, 2014 at 4:30 PM, Mark Atherton <markaren1 at xtra.co.nz> wrote:

> A 64 bit int with shift, bit test, and re-load would work, but that needs
> an 8 byte storage quantity...
>
> So it has to be written in C ? Assembler not allowed ? :)
>
> should be possible to build a 6 bit counter using xors and tests -
> basically making a counter using cascaded T type flip flops with lookahead
> carry etc. not sure if that can be done in 10 lines of code...
>
> I think the brain may need plugging in backwards for this one.
>
> -mark
>
>
> At 03:36 p.m. 19/11/2014, you wrote:
>
>  I'm building a jumbo LED clock (using 8" 7-segment displays) for the
>> local pool, as I can't read a small analogue clock without my glasses when
>> swimming. The PCBs are on their way from China as I type....
>>
>> So here is the challenge. Make a C function that usually returns 0, but
>> returns a value of 1 once in every 60 calls calls - just like this:
>>
>> int chocolate_fish(void)
>>
>> {
>>
>>   unsigned counter = 0;
>>
>>    if(counter == 59) {
>>
>>       counter = 0;
>>
>>       return 1;
>>
>>    }
>>
>>    counter++;
>>
>>    return 0;
>>
>> }
>>
>> Now to make it hard. You can't use any math operations - no addition,
>> subtraction multiplication or division, including the increment/decrement
>> operations.
>>
>> Bonus points for using no more static memory than one byte, and code less
>> than 10 lines - with each statement on a line of their own.
>>
>> Mike
>>
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>
>
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