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   Messages 26 - 27 of 27 - Collapse all  -  Translate all to Translated (View all originals) < Older 
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Frode Vatvedt Fjeld  
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 More options Sep 11 2002, 8:27 pm
Newsgroups: comp.lang.lisp
From: Frode Vatvedt Fjeld <fro...@acm.org>
Date: Thu, 12 Sep 2002 02:27:13 +0200
Local: Wed, Sep 11 2002 8:27 pm
Subject: Re: compiled code
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Matthew Danish <mdan...@andrew.cmu.edu> writes:
> But how does it know that the result is a fixnum?

Agreed. That looks to me to be a false conclusion by the
compiler. Unless the (safety 0) somehow makes it okay.

--
Frode Vatvedt Fjeld


 
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Erik Naggum  
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 More options Sep 11 2002, 10:26 pm
Newsgroups: comp.lang.lisp
From: Erik Naggum <e...@naggum.no>
Date: 12 Sep 2002 02:26:48 +0000
Local: Wed, Sep 11 2002 10:26 pm
Subject: Re: compiled code
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* Matthew Danish
| Very nice output =)  But how does it know that the result is a fixnum?

  Allegro CL has a compiler optimization switch that makes declared fixnums
  remain fixnums.  It defaults to true only when speed is 3 and safety 0.  If
  you turn it off, the same Common Lisp code produces more machine code:

   0: c1 f8 02    sarl  eax,$2
   3: c1 fa 02    sarl  edx,$2
   6: 03 c2       addl  eax,edx
   8: ff a7 87 00 jmp   *[edi+135]      ; sys::fixnum-or-bignum
      00 00

  The shifts convert from the fixnum representation (two type tag bits) to the
  machine integer and the tail-called function will shift the sum back if there
  is space or cons a bignum if not.

--
Erik Naggum, Oslo, Norway

Act from reason, and failure makes you rethink and study harder.
Act from faith, and failure makes you blame someone and push harder.


 
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