OpenEuphoria

Re: Euphoria bug

• Posted by Robert Craig <rds at RapidEuphoria.com> Sep 14, 2005
• 636 views

Bob Thompson wrote:
> --I've been getting a lot of misleading results during benchmarking
> --of various large structures which prompted an investigation.
> --The following example shows an anomaly I found.
> --Run the programme with and without releasing the commented loop(s)
> --and note the speed of the loops. 1D structures are fast and behave normally.
> 
> sequence s
> atom t
> object data
> constant repeats = 1000000, len = 1000
> 
> s = repeat(repeat({}, len), len)
> 
> -- --this loop always appears to be fast and speeds up all following loops
> -- t = time()
> -- for n = 1 to repeats do
> -- s[length(s)][length(s)] =  {3333, 7777}
> -- data = s[length(s)][length(s)]
> -- end for
> -- ?time()-t
> 
> -- t = time()
> -- for n = 1 to repeats do
> -- s[999][999] =  {3333, 7777}
> -- data = s[999][999]
> -- end for
> -- ?time()-t
> 
> t = time()--identical to the second loop
> for n = 1 to repeats do
> s[999][999] =  {3333, 7777}
> data = s[999][999]
> end for
> ?time()-t
> 
> machine_proc(26,0)

Thanks for reporting it.
I've duplicated the problem on my machine.
It seems that almost any change you make can cause
it to run fast. I haven't had time to track it down,
but working with a stripped down version suggested by
Matt Lewis, I found that simply changing:
   data = s[999][999]
to:
   data = s[998][999]
Makes it fast. 

sequence s
atom t
object data
constant repeats = 1000000, len = 1000

s = repeat(repeat({}, len), len)

-- s[1][1] = 0 -- makes it fast - Matt Lewis

t = time()--identical to the second loop
for n = 1 to repeats do
    s[999][999] =  {1, 1}
    data = s[999][999]
--  data = s[998][999] -- makes it fast
end for
?time()-t

This makes me think there might be a
quirky situation here to do with reference counts,
that causes a sequence to be copied on overwrite (slow case) 
or not copied (fast case).

It's getting late. 
I'll investigate it tomorrow.

Regards,
   Rob Craig
   Rapid Deployment Software
   http://www.RapidEuphoria.com