* bug#8940: Evidence of bug in `random'
@ 2011-06-27 3:40 Rafael D Sorkin
2011-07-09 8:15 ` Paul Eggert
0 siblings, 1 reply; 2+ messages in thread
From: Rafael D Sorkin @ 2011-06-27 3:40 UTC (permalink / raw
To: 8940
The following report refers to this version of emacs:
GNU Emacs 23.2.1 (x86_64-pc-linux-gnu, GTK+ Version 2.24.4) of
2011-04-04 on crested, modified by Debian
Hello,
I'm sorry to submit a rather vague report, but I have found
strong evidence of some sort of problem with the random number
generator `random'. I see the difficulty only indirectly in
some simulations I'm running. Results obtained from elisp's
`random' disagree by over 6 sigma with results obtained from
`mt-random' (the "mersenne twister") or from the built-in
functions in both clisp and sbcl.
Perhaps you could check for changes from earlier versions.
The problem seems absent from version 22.1.1.
Here's some info on the hardware from /proc/cpuinfo
processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 15
model name : Intel(R) Xeon(R) CPU E5335 @
2.00GHz
stepping : 11
cpu MHz : 1995.000
cache size : 4096 KB
fpu : yes
fpu_exception : yes
cpuid level : 10
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep
mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2
ss syscall lm constant_tsc arch\
_perfmon pebs bts rep_good nopl tsc_reliable aperfmperf pni
ssse3 cx16 hypervisor lahf_lm dts
bogomips : 3990.00
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:
Thanks,
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
Rafael Sorkin
Perimeter Institute for Theoretical Physics
31 Caroline Street North
Waterloo, ON N2L 2Y5
Canada
~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~
^ permalink raw reply [flat|nested] 2+ messages in thread
* bug#8940: Evidence of bug in `random'
2011-06-27 3:40 bug#8940: Evidence of bug in `random' Rafael D Sorkin
@ 2011-07-09 8:15 ` Paul Eggert
0 siblings, 0 replies; 2+ messages in thread
From: Paul Eggert @ 2011-07-09 8:15 UTC (permalink / raw
To: Rafael D Sorkin; +Cc: 8940-done
Thanks for that bug report. Recently, I independently found
severe nonrandomness in 'random' and installed a patch
in the Emacs trunk as bzr 104596
<http://bzr.savannah.gnu.org/lh/emacs/trunk/revision/104956>.
This patch should appear in the next major release of Emacs.
Please give the patch a try. It may not be as good as the Mersenne
twister etc., but it should be as good as Emacs 22 was.
I'll mark this bug report as 'done' for now, but we can
reopen it if the patch doesn't fix your problem.
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