How to make Python run as fast (or faster) than Julia

[bartc]

On 26/02/2018 13:42, Ned Batchelder wrote:
> On 2/26/18 7:13 AM, bartc wrote:

>> A C version is given below. (One I may have messed around with, which 
>> I'm not sure works properly. For an original, google for Marsaglia and 
>> KISS64 or SUPRKISS64.)
>>
>> Most integers are unsigned, which have well-defined overflow in C 

> With proper 64-bit masking (def only64(x): return x & 
> 0xFFFFFFFFFFFFFFFF), the Python version produces the correct answer 
> using a reasonable amount of memory.

I did try sometime like that, but I must have missed something because I 
didn't get quite the same results as a working version.

And with interpreted code, you tend not to test using loops of a billion 
iterations.

  Well, once you notice that the
> Python code had N=1e5, and the C code had N=1e9 :)   If you want to 
> experiment, with N=1e5, the final number should be 5255210926702073855.

OK, I'll try that.

> Also, I note that you said, "Most integers are unsigned", but the C code 
> has them all declared as signed?  It doesn't seem to have mattered to 
> your result, but I'm not an expert on C portability guarantees.

The C code I first pasted used 'unsigned', but the main program logic 
wasn't right, and I found another version that looked better. That one 
used 'signed' for some reason, which I completely missed.

Even if with C it works with either, the signed version might have 
'undefined behaviour'. As said, google for the original; the ones I can 
see have 'unsigned'. But I can also see a Fortran version that just uses 
'integer*8', which I believe is signed 64-bit.

-- 
bartc