Re: strlen(), K+1: clarification

In article <47c4392f.765110578@xxxxxxxxxxxxx>, Richard Harter
<cri@xxxxxxxx> writes
This little bit of ecentricity has its points. The computation
of the terminating value is automatically hoisted out of the loop
body. The new terminating condition is a comparison with 0,
usually a more efficient test than a comparison against a
non-zero value.

As a sociological and psychological note, I opine that it is good
practice to preferentially write descent loops rather than ascent
loops. Sometimes one is preferable, sometimes the other, and
often it doesn't matter.

I disagree. Loops should be written using the most natural form to match
the underlying problem, rather than reversing them in the hope of some
slight efficiency.

From experiment, where the compiler can determine the number of loops
before it starts, it compiles it into the most efficient code anyway.
Thus given:

for (i = 0; i < k - 1; i++)
foo ();

gcc compiled it into the equivalent of:

i = k - 1
for (int ii = i; ii > 0; i--)
foo ();
or:
i = k - 1
for (int ii = i - 1; ii >= 0; i--)
foo ();

(I forget which and can't be bothered to go back and check.)

--
Clive D.W. Feather | Home: <clive@xxxxxxxxxx>
Tel: +44 20 8495 6138 (work) | Web: <http://www.davros.org>
Fax: +44 870 051 9937 | Work: <clive@xxxxxxxxx>
Please reply to the Reply-To address, which is: <clive@xxxxxxxxxx>
.

Relevant Pages

  • Re: foreach and stack, iterating from the bottom-up?
    ... Andreas Leitgeb wrote: ... For loops are allowed with iterators. ... Foo foo = iter.next; ... And without scaring the people with falsehoods about 'for' loops, ...
    (comp.lang.java.programmer)
  • Re: Maximum number of bits
    ... I posted contents of a lookup table with 17 rows to cover the first set of combinations. ... The "nested loops within loops" refers to a procedural looping solution. ... CREATE TABLE Foo; ... > management and physical I/O (unless you have 40 GB of RAM dedicated to ...
    (microsoft.public.sqlserver.programming)
  • Strange shellscript behaviour?
    ... Both loops reads lines from a file and modifies FOO. ... echo $FOO # But here it is 4 ...
    (comp.unix.programmer)
  • Re: Sorry for the NOOB question..
    ... do/while loops are more difficult to master ... more complex than "while (foo) {something)". ... cond is false), ...
    (comp.lang.c)