[pypy-dev] Re: Ints vs Longs

Michael Hudson mwh at python.net
Mon Oct 13 12:58:33 CEST 2003


Florian Schulze <florian.proff.schulze at gmx.net> writes:

> On Mon, 13 Oct 2003 10:58:14 +0100, Michael Hudson <mwh at python.net> wrote:
>
>> Florian Schulze <florian.proff.schulze at gmx.net> writes:
>>
>>> I just wondered what happens when ints overflow.
>>
>> In PyPy, um, I'm not sure :-) We don't have a long type in the
>> StdObjSpace yet, so I guess you'll get an overflow error.
>>
>>> This question also applies to Psyco.
>>
>> Psyco correctly detects overflow and returns a long.
>>
>> For mulitplication, at least, this is easier in machine code than C...
>
> That's because there is an overflow flag ;)

Exactly :-)

>>> Is a long returned? How much of a speed penalty does occure due to
>>> this?
>>
>> I don't know.  It's probably quite substantial.
>
> Hmm, now that you mentioned that Psyco uses machinecode, I think the
> penalty is not *that* high. It depends on how well the processor
> handles the branching, I guess.

Ah, I thought you were asking about how much overhead occurred when
there *was* an overflow.  That could be substantial, as I don't think
psyco knows very much about longs (could be wrong, though).

The overhead of checking for overflow is, as you say, probably not
that high.  I don't know enough about the x86 architecture to say
more.

Cheers,
mwh

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