Re: [Caml-list] Gripes with array

[Damien Doligez <damien.doligez@inria.fr>]

On Sep 9, 2004, at 18:58, Jon Harrop wrote:

>>> Also, can Array.init be made to fill the elements only once?
>> No, that's impossible without breaking the GC invariants.
>
> Could it not even be done by dragging Array.init inside the compiler, 
> giving
> it the same status as Array.make?

Not without implementing such horrors as Christophe described.  I don't 
much
like the idea of introducing lots of bugs while slowing down the whole 
GC,
even for programs that don't use arrays.  An intermediate solution would
be to make a "Array.unsafe_make" primitive, which would use memset 
instead
of initialising the array properly.  If you enter this as a feature wish
in the BTS, I'll look into it.

> Measuring memset from C gives me 0.0311secs. So element-setting must 
> be at
> least 10% of Array.init. Also, the array_init function is surprisingly 
> fast,
> presumably due to "f" not being inlined into Array.init but being 
> inlined
> into array_init.

That would confirm my intuition that the calls to f dominates the
initialisation time.

-- Damien

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