On Aug 22, 2013, at 3:05 AM, Diederik Meijer | Ten Horses
<diede...@tenhorses.com> wrote:
> What actually speeds things up significantly is to revert back to NSString
> and use NSRegularExpression.
> I now needs seven seconds on iPad3 to handle >600 replacement actions. This
> is, in itself a VERY long time
Indeed.; that’s incredibly slow. You should be able to do this in a handful of
milliseconds. Don’t make your users suffer through a progress meter because you
couldn’t find the right optimization :)
The right way to do this is by scanning through the original string and writing
to a new mutable string. Using replaceCharacters on a mutable string isn’t much
of a speedup because it keeps copying characters in the mutable string over and
over (and copying the entire string if its buffer needs to grow.)
create the empty output mutable string with sufficient capacity (i.e. maybe 2x
the input string length)
set pos to 0
repeat
find next instance of marker in original string starting from index
‘pos’
if none found
break
append input characters from ‘pos’ to start of marker to output string
append replacement characters to output string
advance ‘pos’ to end of marker
end
I would guess that most algorithms textbooks describe things like this in more
detail.
—Jens
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