DJ Bernstein's str library

[Peter Davies]

Hi all,

Plagued by the (to me) non-obvious functionality of DJB's str.h library, I
started looking at the source and what I saw took a while to make sense.

Each function runs an infinite loop, which iterates though a char* - in
order to search for needles or calculate a string length or whatever. What
got me was that each of the infinite loops held 4 identical statements:

for (;;) {
if (!*t) break; if (*t == ch) break; ++t;
if (!*t) break; if (*t == ch) break; ++t;
if (!*t) break; if (*t == ch) break; ++t;
if (!*t) break; if (*t == ch) break; ++t;
}
(in str_chr.c) and

for (;;) {
if (!*t) return t - s; ++t;
if (!*t) return t - s; ++t;
if (!*t) return t - s; ++t;
if (!*t) return t - s; ++t;
}
(in str_len.c)

Does anyone have any ideas as to why this is done? All I can think of is
that 4 chars=32bits and that nicely fills a register.

--
Peter Davies

[Poldie]

Isn't it just an example of an unrolled loop, reducing the overhead (if
any) of the test for termination of the for loop?

[Flash Gordon]

Poldie wrote:

Isn't it
Isn't what? Provide context, there is no guarantee that everyone who
sees your post has seen the message you are responding to. Search the
group for "Google context" to find out how much of a problem this is and
how to work around the crap interface Google provide. Then complain at
Google for them making you look like a fool.
just an example of an unrolled loop, reducing the overhead (if
any) of the test for termination of the for loop?

Once upon a time compilers were not very good at optimising. These days
you are generally better off leaving it to the compiler.
--
Flash Gordon
Living in interesting times.
Although my email address says spam, it is real and I read it.

[Jordan Abel]

On 2005-10-27, Flash Gordon <sp**@flash-gordon.me.uk> wrote:

Poldie wrote:

Isn't it

Isn't what? Provide context, there is no guarantee that everyone who
sees your post has seen the message you are responding to.

And that is why the References: header was invented.

yes, it's irritating. so is reading people complaining about it.

--
I was half-tempted to not quote you.

[Poldie]

> Provide context, there is no guarantee that everyone who

sees your post etc etc

Yawn. Guess what - I don't care.
Once upon a time compilers were not very good at optimising. These days
you are generally better off leaving it to the compiler.

He wasn't asking if optimization is worth performing 'these days' - he
was asking if perhaps that technique was related to registers, and I
was telling him that I didn't think it was. Your opinion of the
efficiency of current compiler optimization techniques is irrelevant.

[Kenny McCormack]

In article <qt************ @news.flash-gordon.me.uk>,
Flash Gordon <sp**@flash-gordon.me.uk> wrote:

Poldie wrote:

Isn't it

Isn't what? Provide context, there is no guarantee that everyone who
sees your post has seen the message you are responding to. Search the
group for "Google context" to find out how much of a problem this is and
how to work around the crap interface Google provide. Then complain at
Google for them making you look like a fool.

You (and others, such as Keith) are wasting your breath. They'll never get
it. And I'll tell you why.

Imagine that there's a mouse - and the mouse is the Usenet. You and I can
see that it is a mouse and we behave accordingly. But now there is a class
of users (we'll call them "googlers") that are wearing these funny weird
glasses that make them see not a mouse, but an elephant. Seeing an
elephant (i.e., the Usenet as a web page), they also behave accordingly.
And no amount of verbiage from us is going to convince them that it's not
an elephant - that it is only a mouse.

To make this more clear, to a googler, it doesn't make any sense to "quote"
(whatever the heck that is...), in fact, to do would be absurd, when all
the rest of the articles in the thread are right there in front of their
faces (just as clear as the trunk on that mouse, er, elephant). And no
amount of verbiage from us is going to convince them not to believe what
they see. The point is you can *never* convince someone that what they see
isn't reality. The only way you can address the problem is to help them
fix their eyesight (or help them remove their funny glasses).

[Poldie]

> But now there is a class

of users (we'll call them "googlers") that are wearing these funny weird
glasses

There is also a class of users (we'll call them "net nerds") who spend
an inordinate amount of time on the internet, and who seem to suffer
delusions of grandeur which make it very very important to them that
every last character they type is preserved, in perfect context, for
all eternity, and the very thought that some people might be treating
the odd thread in the odd group with less than complete seriousness and
simply trying to answer a poster's question is just beyond the pale.

You are hereby served with the requirement that you admonish 25 Usenet
posters for top-posting in the next 60 minutes. Go get'em, tiger!

[Peter Davies]

On Thu, 27 Oct 2005 13:20:50 +0000, Kenny McCormack whinged:

In article <qt************ @news.flash-gordon.me.uk>,
Flash Gordon <sp**@flash-gordon.me.uk> whinged:

[schnip]

Please continue whinging here. It will help me and others who are
interested in the original thread to differentiate between usefulness and
fluff.

Note that you are not the first to complain about Google and its effect on
Usenet. However much I may agree with your opinions on that topic, it is
in my opinion extremely rude to hijack threads for the purposes of being
bitchy.

--
Peter Davies

[Neil Cerutti]

On 2005-10-27, Poldie <Po****@gmail.c om> wrote:

Provide context, there is no guarantee that everyone who
sees your post

etc etc

Yawn. Guess what - I don't care.

It's obviously your right to hold that attitude, but it is only
to your advantage if you prefer being ostracized.

--
Neil Cerutti

[Poldie]

> It's obviously your right to hold that attitude, but it is only

to your advantage if you prefer being ostracized.

Who are you calling an ostrich?