OpenEuphoria

Re: Interesting Experiment With String/Sequence Slicing

• Posted by slie at theage.fairfax.com.au Aug 21, 2001
• 399 views

hi Robert,

i have tried as you have suggested but have came
across more problems that i havent anticipated
because the string that i am searching for
are tag types eg.  <TD> ** NAME ** </TD>
and i run into problem when </TD> or parts of
it occur on the next line.  so i will still have to
read all the text into one big sequence and then
do the string slicing and chopping. i suppose i can
very much live with slicing but i am just wondering
could there be a function similar to slicing but only
works on strings and is much faster by moving blocks
of memory rather than copy one sequence element
to another one at a time.  however maybe thats not possible
because the sequence is not represented as a set of
continuous memory block.   

today i also came across something very interestings.

example 1
for i=1 to 1000 do
     sLine2 = sLine
     sLine2 = sLine2[2..length(sLine2)]
end for

example 2
for i=1 to 1000 do
     sLine2 = sLine
     sLine3 = sLine2[length(sLine2)-10..length(sLine2)]
end for

example 2 was faster than example 1 by a factor of 100
so my thought was that example 1 was slower because it
had to copy more items when doing the slicing.  but then again i 
thought why is it copying items, as Derek had suggested 
in the case of example 1 we could just blank out/remove  the first 
sequence element and return the sLine2 as is.  If this case is true
then the term 'slicing' could not be taken literally because it is
more like a copy operation.  flame me if i am wrong.

regards,
sam lie
Down Under, Australia



t = time()
for i=1 to 1000 do
 sLine2 = sLine
 sLine3 = sLine2[length(sLine2)-10..length(sLine2)]


----- Original Message ----- 
From: "Robert Craig" <rds at RapidEuphoria.com>
To: "EUforum" <EUforum at topica.com>
Sent: Wednesday, August 22, 2001 2:00 AM
Subject: Re: Interesting Experiment With String/Sequence Slicing


> 
> Sam Lie writes:
> > i have ran the profiler and the bottle neck still
> > shows up when doing string slicing. 
> 
> I gather from your earlier private e-mail that you are reading huge
> strings from a file and running match() on them.
> Or perhaps the string *is* the whole file?
> 
> Since match() starts at the beginning of a sequence,
> and stops when it encounters a match, I gather
> you are slicing the 50K strings to look for further matches.
> 
> Try reading and searching one line at a time using gets().
> You won't be copying a huge string when you have a match,
> and you'll make better use of the Pentium on-chip cache,
> e.g.
>       object line
>       integer fn
> 
>       fn = open("myfile.html", "r")
>       while 1 do
>             line = gets(fn)
>             if atom(line) then
>                 exit
>             end if
>             if match("foobar", line) then
>                 .....
>             end if
>       end while
>       close(fn)
> 
> After doing the above, if you are still convinced that 
> slicing is the culprit, you could write your own match() 
> that locates multiple occurrences without slicing. 
> (There may be an example in the mailing list archives.)
> 
> Regards,
>    Rob Craig
>    Rapid Deployment Software
>    http://www.RapidEuphoria.com
> 
> 
> 
> 
> 
> 



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