Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>> I'm merely 
>> pointing out that the errors you describe comes from treating "int"s as 
>> "integers". There's no such thing as an "unsigned integer", only an 
>> "unsigned int".  It was a nit, nothing more. :-)
> 
>   I didn't understand that.

The C declaration of
   unsigned int X;
does not allocate an integer variable.

You wouldn't need signed/unsigned conversion rules if you were working 
with integers instead of int's.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Warp wrote:
> Darren New <dne### [at] sanrrcom> wrote:
>>>   Integral types which support unlimited precision can *not* be as efficient
>>> as CPU-register-sized integers
> 
>> Sure they can. I've used many computers where the unbounded arithmetic 
>> was just as fast as the bounded arithmetic when you stayed within bounds.
> 
>   The only way for that is that the CPU has explicit support. 

Right. Which is why, a few months ago, I was claiming that processors 
for the last few generations have been targeted at C code, rather than C 
code being particularly good for general processors.

Processors already do this for floating point. I'm not sure why they 
don't for integers any more, other than C not supporting it, so it's not 
put in.

Of course, if your register size is such that you need to do 
multi-instruction operations for usably-sized ints anyway (e.g., you're 
on a 6502 CPU), you might as well, since it's all part of the same thing 
anyway.

>   AFAIK x86 processors do not have such a feature. The only thing an integer
> overflow will do is to set a flag, which can then be checked with additional
> opcodes, at the cost of additional clock cycles.

Right. But you hadn't qualified your statement to x86 processors.

>   This would require even more CPU support than simply checking for a
> register-sized integer overflow, as you would have to check if the value
> goes out of arbitrarily-set boundaries (instead of just overflowing or
> underflowing over). In other words, you would have to be able to tell
> the CPU, at no clock cycle cost, "if this register ever gets a value
> smaller than this or larger than this, throw an exception". I have hard
> time believing any existing CPU has such a feature.

Burroughs B-series, for example. Since the CPU also checked array 
bounds, it had that sort of math built in. I'm not sure if it's still 
"existing", but IBM had versions of this in production not too long ago. 
iAPXyaddamumble or something like that.

Modern processors running Ada add another check, yes. It can be less 
efficient, unless you declare the variable to be a "modulo integer", 
which then works like C's integers.

On the other hand, if I'm writing the code for a weapon, I'd rather have 
it throw an exception than suddenly negate the amount it decides it 
needs to rotate to fire towards the enemy. ;-)

>   With normal CPUs the compiler would have to put a comparison and a
> conditional jump after each single operation done to the variable, at the
> cost of additional clock cycles. 

I expect you can optimize out a lot of this, but yes.  You can probably 
do a lot by putting in smaller bounds checks near the beginning of a 
routine, for example, to prove that nothing in the middle of a formula 
goes out of bounds.

>   Unless you give me an understandable and logical explanation of how these
> kinds of checks could be implemented without making the code slower, I just
> cannot believe it's possible.

As I said in the previous post, I've used a number of processors where 
it's the case.

>   Sure, there are some other CPUs which do, but in practical terms that
> doesn't help the average programmer too much.

I wasn't disputing an assertion that x86 architectures need more 
processing. I was disputing that it's impossible in general and by 
definition to have no overhead for multi-precision math traps.

I would also dispute that the default should be "do the wrong thing 
fast". I would argue that the *default* should be "do the right thing, 
and let me tell you where it's too slow."  Premature optimization and 
all that, you know.

C isn't the way it is because it's efficient that way. C is the way it 
is because the compiler had to fit in 12K. The reason C has ++ and -- is 
it was built into the addressing hardware of the machines C was first 
implemented on, not because it's particularly good for programming.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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Orchid XP v7 wrote:
> Sadly, M$ has managed to convince the general population that it is 
> "normal" for computers to not work propperly.

I agree. If you bought a new car and it randomly stalled once a month, 
you'd be taking it in for warranty service.

On the other hand, computer programs are pretty much the most 
complicated things ever created, almost be definition. If two chunks are 
the same, you take one out. It's 100% complex.

> There's a difference between "taking advantage of" and "wasting".

Not for MS.

> most businesses actually want is a tiny OS to run their *real* 
> applications on top of...)

Not especially. They want the applications to run. If the OS can support 
getting those applications written faster or cheaper, then OS "bloat" is 
a good thing.

-- 
   Darren New / San Diego, CA, USA (PST)
     Remember the good old days, when we
     used to complain about cryptography
     being export-restricted?

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> Sadly, M$ has managed to convince the general population that it is 
> "normal" for computers to not work propperly. If you bought a washing 
> machine and it didn't work properly, you'd take it back and demand a 
> refund. But when people buy a computer and the software on it doesn't 
> quite work properly, people just think this is "normal" and "acceptable". 
> This, truely, is M$'s contribution to the field of computer science.

Yeh you keep going on about how bad MS are, but I just don't see this.  Our 
whole company (as do many others) run on MS servers and MS run desktops.  We 
really don't see the level of problems you describe.  Last problem we had in 
the office was when IT installed a buggy print driver on the print server, 
it caused Word (well, any application that had print functionality) to crash 
randomly.  Of course everyone blamed MS, but then IT fixed the print driver 
and everything has been fine since.  I don't even remember the last time 
Word or any Office program crashed.

> I *was* going to sell my old CPU on ebay. I mean, it's a moderately old 
> now, but I paid about £250 for it when I got it.
>
> However, this was before I discovered that you can buy it new (exact same 
> model, clock speed, socket, everything) for £21.

Well at least you checked the price.  Some people just say "bought new for 
X, will sell for X/2", when in reality it's worth X/10 or 20.

> £21. Retail boxed. With a warranty.
>
> Who the hell is going to buy a second hand one?

You'd be surprised, second hand prices of computer components seem to sell 
at a fraction under the new price.  I guess there are a lot of people who 
are looking to save just a few £££s by getting second hand.  And it's not 
like most other things where they look old or don't work properly, a CPU is 
a CPU, it either works or it doesn't.

> Do you even remember when WinXP first came out? And how everybody has 
> utterly horrified at the minimum hardware requirements to make it function 
> acceptably? It's been around so long now that everybody seems to have 
> forgotten that XP takes four times as much hardware to do the same thing 
> as older OSes managed to do quite happily...

If it does the same thing, why are you using it?  Why does anyone use it if 
it does the same thing as previous versions?

> (And then there's the sad fact that M$ doesn't know the difference between 
> "operating system" and "entertainment system". Even in the "pro" version 
> of XP, you still get lots of silly toys like games and video players and 
> so forth that I have to spend ages uninstalling. Surely what most 
> businesses actually want is a tiny OS to run their *real* applications on 
> top of...)

Gee, I'd hate to work at your company where the IT people don't even let you 
watch videos or play an odd game of Internet Reversi during a break. 
Actually some of our customers send us video clips of problems sometimes, it 
would be a bit embarrassing if we had to explain how we chose an IT system 
that didn't allow us to watch them...

People also use WinXP Pro at home you know, I think everyone in my family 
and even my gf on her laptop has the Pro edition.

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>  (Why would anyone even want to install linux in a 386? Well, if you
> have one laying around, it makes a supercheap firewall or small-scale ftp
> server, for instance.)

If you want to go with MS for this sort of thing then people use DOS.  My 
camera uses DOS as an OS, as does the oven we have here in the lab - and it 
even does graphics :-)  Admittedly you can't expect to run Word2003 on it, 
but for the sort of thing you probably want to do with a 386 it would be 
fine.

Or you could install Win95 or Win3.1 if you really wanted Windows.

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> I agree. If you bought a new car and it randomly stalled once a month, 
> you'd be taking it in for warranty service.

It would probably be a software problem :-)

> On the other hand, computer programs are pretty much the most complicated 
> things ever created, almost be definition. If two chunks are the same, you 
> take one out. It's 100% complex.

Yep, even on something relatively much simpler, like the radio in a car, it 
is the software that causes the biggest headaches.  We can develop and test 
the hardware usually in two or three 6 month blocks, but it always the 
software that requires *way* more time and is usually the reason for 
requested hardware changes, extra builds and delays.

If MS wanted this level of reliability on their software, which is 10s or 
100s times more complex, it would take them forever to release anything.  It 
just wouldn't work, they would go bankrupt.

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Darren New <dne### [at] sanrrcom> wrote:
> The C declaration of
>    unsigned int X;
> does not allocate an integer variable.

> You wouldn't need signed/unsigned conversion rules if you were working 
> with integers instead of int's.

  I may be unusually dense here, but I still can't understand.

-- 
                                                          - Warp

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scott <sco### [at] laptopcom> wrote:
> >  (Why would anyone even want to install linux in a 386? Well, if you
> > have one laying around, it makes a supercheap firewall or small-scale ftp
> > server, for instance.)

> If you want to go with MS for this sort of thing then people use DOS.

  Good luck trying to log in and configuring it remotely. Or running any
server software in it, for that matter.

> Or you could install Win95 or Win3.1 if you really wanted Windows.

  Win95 in a 386? Hardly.

-- 
                                                          - Warp

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And lo on Wed, 24 Oct 2007 17:56:57 +0100, Jim Henderson  
<nos### [at] nospamcom> did spake, saying:

> On Wed, 24 Oct 2007 12:48:01 -0400, Jim Henderson wrote:
>
>> The problem doesn't
>> start in the software development houses, it starts at school when
>> students are learning how to code and are taught bad habits from the
>> start.
>
> As an example, I remember a core component of a popular server OS that
> would, under certain circumstances, display negative disk space free.

On a similar note I see that the new PS3 exclusive Ratchet & Clank may  
fail to install if you have *too much* hard drive space, the suggested  
solution is too add around 500Mb (Why 500?) as one person commented "I  
love how in this day and age of downloadable patches, QA for games has  
gone by the wayside."

-- 
Phil Cook

--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com

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>> >  (Why would anyone even want to install linux in a 386?
>
>> If you want to go with MS for this sort of thing then people use DOS.
>
>  Good luck trying to log in and configuring it remotely. Or running any
> server software in it, for that matter.

Things like cameras and lab equipment don't really need that.  Maybe that's 
one reason why cameras use USB and not LAN or WLAN - it's just too 
hard/impossible to get a network stack on DOS?

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