NetNews Offline 2/NetNews Offline Volume 2.iso/news/comp/lang/c++-part2/14291

Internet Message Format | 1996-08-05 | 1.8 KB

Path: invincible.astro.uu.se!daniel
From: [e-mail] (Daniel Kallander)
Newsgroups: comp.lang.c++
Subject: Re: Reverting of big array ?
Date: 29 Mar 1996 18:24:04 GMT
Organization: Uppsala University
Distribution: world
Message-ID: <4jh9s4$[e-mail]>
References: <Pine.SOL.3.91.960326132111.6385A-100000@evolution> <[e-mail]>
NNTP-Posting-Host: invincible.astro.uu.se

In article <[e-mail]>, Paulo Eduardo Neves <[e-mail]> writes:
|> Thomas wrote:
|> >
|> > I need to revert an array (of chars).
|> > I used the folowing code:( l=length of array)
|> >
|> >   char *rev=new char[l+1];
|> >   for(i=l-1,j=0;i>=0;i--,j++)  rev[j]=seq[i];
|> >   rev[j]='\0';
|> >
|> > this code works, but is terribly slow, when using an string with
|> > size ~ 6000.
|> > doing the same with the unix command 'rev' takes 1/2 second.
|> >
|> > Any ideas  ???
|> >
|> > -thomas
|> >
|> > Sicheritz Ponten Thomas E.              UPPSALA UNIVERSITY
|>

Don't use chars, use integers of the same bit length as the number
of bits that your processor uses internally, which should be the
same as the C 'int' type. Because the byte length of your character
array probably isn't divisible with the number of bytes in an
'int', you have to be careful at the endpoints. In that case,
it is probably easiest to just revert a few more bytes than
necessary.
This should make a substantial difference.

Moreover, you don't really need more than one of your two counters.
j is a simple function of i, and thus unnecessary.
--
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Daniel Kallander, e-mail:[e-mail]
Uppsala Astronomical Observatory
Theoretical Astrophysics
SWEDEN
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