From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <zsh-workers-return-10759-mason-zsh=primenet.com.au@sunsite.auc.dk>
Received: (qmail 3547 invoked from network); 14 Apr 2000 12:15:41 -0000
Received: from sunsite.auc.dk (130.225.51.30)
  by ns1.primenet.com.au with SMTP; 14 Apr 2000 12:15:41 -0000
Received: (qmail 17019 invoked by alias); 14 Apr 2000 12:15:34 -0000
Mailing-List: contact zsh-workers-help@sunsite.auc.dk; run by ezmlm
Precedence: bulk
X-No-Archive: yes
X-Seq: 10759
Received: (qmail 17005 invoked from network); 14 Apr 2000 12:15:34 -0000
Date: Fri, 14 Apr 2000 13:15:00 +0100
From: Peter Stephenson <pws@cambridgesiliconradio.com>
Subject: Re: PATCH: fix for (#s) and (#e) in param substs
In-reply-to: "Your message of Fri, 14 Apr 2000 15:42:05 +0400."
 <000601bfa606$750527f0$21c9ca95@mow.siemens.ru>
To: zsh-workers@sunsite.auc.dk (Zsh hackers list)
Message-id: <0FT000MMUA0ZD3@la-la.cambridgesiliconradio.com>
Content-transfer-encoding: 7BIT

> Just a question - is there any speed penalty in using / instead of # or
> %?

There will be some effect, since there is no optimisation to look for an
initial (#s) or final (#e) in the parameter substitution code, unlike # and
% where the start/end anchor is hard-coded.  I had to think about this...

Ksh form        Form with explicit anchors
${..#..}        ${(S)../(#s)..}
${..##..}       ${../(#s)..}

In the second form in each case, we still advance up the string looking for
matches, so it's slower, particularly for a long test string.  However, the
test will always fail on the first attempt, so it doesn't depend on the
complexity of the pattern after the anchor.

${..%%..}       ${../..(#e)}

Not much difference, since in the former case we march up the string until
we find a match, pretty much as in the second case.

${..%..}        ${(S)../..(#e)}

These could be quite a lot slower with a fixed tail for a long string,
e.g. ${(S)foo/.c(#e)} where $foo is long, since that has to march up the
string to find a match, then shorten from the end (though the latter will
always fail on the second match so isn't really a problem).  But with a
fixed string you wouldn't bother with the (S) parameter flag.

Anyway, I'd be interested to hear if you can notice any difference using /.

It wouldn't be that hard to do special cases.  I don't know if it's worth
it.  I expect these bits are only going to be used by the real zsh nutcases
:-).

-- 
Peter Stephenson <pws@cambridgesiliconradio.com>
Cambridge Silicon Radio, Unit 300, Science Park, Milton Road,
Cambridge, CB4 0XL, UK                          Tel: +44 (0)1223 392070