New subject: Help with bit bashing code: differences between C and CL

9 Nov 2023


      Thanks.
This is weird.  The C and Fortran versions seem to agree.
Marco
On Thu, Nov 9, 2023 at 9:49 PM Frank Gönninger | Gönninger B&T <
frank.goenninger@goenninger.net> wrote:
...
Hi Marco,
on AllegroCL 11.0 beta Enterprise Edition I get diverging results starting
at j = 21…
Lisp: j = 21; ss = 0.00028959847986698150
C:      j = 21; ss = 0.00028959847986698151
FWIW …
Best,
Frank
*Von: *owner-lisp-hug@lispworks.com im Auftrag von "Marco Antoniotti
(as marco dot antoniotti at unimib dot it)" lisp-hug@lispworks.com
*Antworten an: *Marco Antoniotti marco.antoniotti@unimib.it
*Datum: *Donnerstag, 9. November 2023 um 21:23
*An: *LispWorks lisp-hug@lispworks.com, Discussion list for Common Lisp
professionals pro@common-lisp.net
*Betreff: *Help with bit bashing code: differences between C and CL
Dear all,
I am hitting a wall with the attached code in CL and C versions.  For
those interested, this is code lifted from Knuth's pages on random number
generation (https://www-cs-faculty.stanford.edu/~knuth/programs.html#rng).
The problem is that there is a discrepancy in the "problem" loop between
the CL and the C and I cannot figure out why, although the culprit may be
that CL does not have "proper" 64 bits ints.
I am running on LW 8.x on an Intel Mac.  I have not tried on other CL
implementations/platforms. I compile the C code with clang (Apple clang
version 15.0.0 (clang-1500.0.40.1)
If you run the code, you will see that the discrepancy appears at 'j = 14'
in the loop.
What gives?
Thanks
Marco
--
Marco Antoniotti, Professor                  tel. +39 - 02 64 48 79 01
DISCo, Università Milano Bicocca U14 2043    http://dcb.disco.unimib.it
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Re: Help with bit bashing code: differences between C and CL