[pypy-dev] Slow int code

[Roger Flores]

Would you like a paste from jitviewer or the source code to run and examine with jitviewer?

-Roger




________________________________
 From: Alex Gaynor <alex.gaynor at gmail.com>
To: Roger Flores <aidembb at yahoo.com> 
Cc: "pypy-dev at python.org" <pypy-dev at python.org> 
Sent: Wednesday, February 27, 2013 12:23 PM
Subject: Re: [pypy-dev] Slow int code
 

In that context large longs means HUNDREDS or THOUSANDS of bits, not 64 :) Can you show us a full runnable example that illustrates this?

Alex



On Wed, Feb 27, 2013 at 12:10 PM, Roger Flores <aidembb at yahoo.com> wrote:

Hi guys.  I've been looking at two simple routines using jitviewer to figure out why they're so much slower than expected.
>
>
>I've also noticed that http://pypy.org/performance.html has the line "Bad examples include doing computations with
>large longs – which is performed by unoptimizable support code.".  I'm worried that my 32 bit int code is falling into this, and I'm wondering what I can do to avoid it?
>
>Trivial code like
>
>if (self.low ^ self.high) & 0x80000000 == 0:
>
>
>is expanding into several dozen asm instructions.  I'm suspecting that lines like 
>
>self.low = (self.low << 1) & 0xffffffff
>
>
>with it's shift left are convincing the jit to consider the int to need 64 bits (large long?) instead of 32.
>
>
>Ideas?  The asm is clearly operating on QWORDs and calling routines to do the bit arithmetic instead of single instructions.  Is this what that line in performance.html is warning about?
>
>
>
>-Roger
>
>BTW Fijal's jitviewer is a *must see* for anyone interested in how pypy makes their code fast!
>
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