[Caml-list] boxing of floats in records/classes

[Caml-list] boxing of floats in records/classes

[Michael Vanier]

Quick question: are mutable float fields in records or classes boxed?  If
so, why?

Mike
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Re: [Caml-list] boxing of floats in records/classes

[Xavier Leroy]

> Quick question: are mutable float fields in records or classes
boxed?

Yes, with the exception of records that have all fields of type float.
In the latter case, the record is represented like a float array, with
each float unboxed.

> If so, why?

Mainly because the runtime system and garbage collector support either
blocks of pointers or blocks of unboxed data, but not mixed blocks
containing both pointers and unboxed data.

- Xavier Leroy
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Re: [Caml-list] boxing of floats in records/classes

[Berke Durak]

On Thu, Sep 26, 2002 at 10:01:03AM +0200, Xavier Leroy wrote:
> > Quick question: are mutable float fields in records or classes
> boxed?
> 
> Yes, with the exception of records that have all fields of type float.
> In the latter case, the record is represented like a float array, with
> each float unboxed.
> 
> > If so, why?
> 
> Mainly because the runtime system and garbage collector support either
> blocks of pointers or blocks of unboxed data, but not mixed blocks
> containing both pointers and unboxed data.

Would it then be false to assume that if you have many floats in a record,
grouping them into a subrecord would reduce the boxing overhead ?
-- 
Berke Durak
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Re: [Caml-list] boxing of floats in records/classes

[Xavier Leroy]

> Would it then be false to assume that if you have many floats in a record,
> grouping them into a subrecord would reduce the boxing overhead ?

This is true, even if you have as little as two float fields.
However, there would be some overhead when accessing one of these
fields, in the case where you need the field value to remain boxed
(i.e. to pass it to a Caml function).  Also, this appraoch sure would
not simplify the compiler :-)

- Xavier Leroy
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