[Numpy-discussion] arange(start, stop, step) and floating point (Ticket #8)

Travis Oliphant oliphant.travis at ieee.org
Thu Feb 9 22:28:02 CST 2006


Sasha wrote:

>Well, my results are different.
>
>SVN r2087:
>  
>
>>python -m timeit -s "from numpy import arange" "arange(10000.0)"
>>    
>>
>10000 loops, best of 3: 21.1 usec per loop
>
>SVN r2088:
>  
>
>>python -m timeit -s "from numpy import arange" "arange(10000.0)"
>>    
>>
>10000 loops, best of 3: 25.6 usec per loop
>
>I am using gcc version 3.3.4 with the following flags: -msse2
>-mfpmath=sse -fno-strict-aliasing -DNDEBUG -g -O3.
>
>The timing is consistent with the change in the DOUBLE_fill loop:
>
>r2087:
>   1b8f0:       f2 0f 11 08             movsd  %xmm1,(%eax)
>   1b8f4:       f2 0f 58 ca             addsd  %xmm2,%xmm1
>   1b8f8:       83 c0 08                add    $0x8,%eax
>   1b8fb:       39 c8                   cmp    %ecx,%eax
>   1b8fd:       72 f1                   jb     1b8f0 <DOUBLE_fill+0x30>
>
>r2088:
>   1b9d0:       f2 0f 2a c2             cvtsi2sd %edx,%xmm0
>   1b9d4:       42                      inc    %edx
>   1b9d5:       f2 0f 59 c1             mulsd  %xmm1,%xmm0
>   1b9d9:       f2 0f 58 c2             addsd  %xmm2,%xmm0
>   1b9dd:       f2 0f 11 00             movsd  %xmm0,(%eax)
>   1b9e1:       83 c0 08                add    $0x8,%eax
>   1b9e4:       39 ca                   cmp    %ecx,%edx
>   1b9e6:       7c e8                   jl     1b9d0 <DOUBLE_fill+0x20>
>
>  
>
Nice to see some real hacking on this list :-)

>My change may be worth commiting because C code is shorter and
>arguably more understandable (at least by Fortran addicts :-). 
>Travis?
>  
>
Yes, I think it's worth submitting.  Most of the suggestions for 
pointer-arithmetic for fast C-code were developed when processors spent 
more time computing than fetching memory.  Now it seem it's all about 
fetching memory intelligently.

The buffer[i]=

style is even recommended according to the AMD-optimization book Sasha 
pointed out.

So, I say go ahead unless somebody can point out something we are missing...

-Travis





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