[Numpy-discussion] String sort

Charles R Harris charlesr.harris@gmail....
Sat Feb 9 15:42:24 CST 2008


On Feb 9, 2008 2:29 PM, Francesc Altet <faltet@carabos.com> wrote:

> Chuck,
>
> One more thing on this.  I've been doing some benchmarking with my
> opt_memcpy() macro in the quicksort_string function, and I should say
> that while it is definitely more efficient than my system memcpy for
> small values of n (the number of bytes to copy), this doesn't keep true
> for all values of n.  For example, for n<16, opt_memcpy() can be more
> than 4x faster than system memcpy (and this is why I naively thought
> that it would be faster in general).  However, for n>80, memcpy beats
> opt_memcpy between a 25% and 100% (depending on whether n is divisible
> by 2, 4 or 8).  This is on my Linux system (Ubuntu 7.10), but perhaps
> with Windows the behaviour can be different.
>
> I think I would be able to come up with a routine that can offer a
> balance between opt_memcpy and system memcpy, but that should take some
> time.  So, until I (or anybody else) do more research on this, I think
> it would be safer if you use system memcpy for string sorting in NumPy.
>

The memcpy in newer compilers is actually pretty good. For integers and such
it sometime compiles inline using integer assignments, but I was loath to
make it the default implementation until >= 4.1.x gcc became more common.
However, strings might be a good place to use it.

Chuck
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