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Re: inline array refs?
- To: email@example.com
- Subject: Re: inline array refs?
- From: firstname.lastname@example.org (Lawrence G. Mayka)
- Date: Sat, 14 May 1994 19:33:00 GMT
- In-reply-to: email@example.com's message of Fri, 13 May 1994 10:40:23 -0500
- Newsgroups: comp.lang.lisp.mcl
- Organization: AT&T Bell Laboratories, Naperville, Illinois, USA
- References: <9405131430.AA01635@cambridge.apple.com>
- Sender: firstname.lastname@example.org (Netnews Administration)
In article <9405131430.AA01635@cambridge.apple.com> email@example.com (Bill St. Clair) writes:
At 10:14 AM 5/13/94 +0000, Karsten Poeck wrote:
>I translated some code to test iterative repair alogirithms from c to LISP.
>The code mainly does fixnum operations and simple-array accesses. By adding
>appropriate (the fixnum ...) and (declare (type (simple-array fixnum (*))
>I managed to get about half the speed of the corresponding c program
>compiled with MPW on the same mac.
>The disassembly of the code shows calls to subroutines
>(jsr_subprim $SP-GETLONG) and
>I suspect that these calls slow down the programm. Does anybody know what
>these routines do and how I could avoid them? I always thought that adding
>enough declarations to a MCL program would give me the same speed as a
>corresponding c program.
>Anyhow I tried to run the same program under LIspWorks 3.2 on a Dec-Alpha
>and to my surprise a quadra 650 was more than two times faster than the
>alpha, even after declaring fixnum-safety = 0. From looking at the
>disassembly I suspect that the arefs are not inlined in LispWorks. Does
>anybody know how I could get LispWorks to inline the arefs too?
I don't know how to inline arefs in LispWorks, but I can help with
your MCL problem. In MCL, an array that is declared to have fixnum
elements is upgraded to have (signed-byte 32) elements. Since these
can be bignums, the code is calling $sp-getlong to convert the
untagged value from the array to an integer. To get rid of the
$sp-getlong call, use a simple-vector, i.e. a simple-array with an
element type of T:
LispWorks has this same implementation characteristic. Make and
declare your vector to be SIMPLE-VECTOR, and you should see almost an
I suggest that vendors instead define an array element type FIXNUM or
(SIGNED-BYTE 30) which just happens to be implementationally identical
to T. Element types from (SIGNED-BYTE 17) to (SIGNED-BYTE 30), and
from (UNSIGNED-BYTE 17) to (UNSIGNED-BYTE 29), should upgrade to
FIXNUM; only beyond those byte sizes should upgrade to full 32 bits
occur (with its concomitant bit-shifting and bignum-checking). This
scheme fits within ANSI Common Lisp rules but still makes the maximum
use of simple word-copying.
Otherwise, naive users who are accustomed to declaring arrays of
FIXNUMs will get an unfavorable view of the implementation's
Lawrence G. Mayka
AT&T Bell Laboratories