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High-level Languages and Speed
nitsudima writes to tell us Informit's David Chisnall takes a look at the 'myth' of high-level languages versus speed and why it might not be entirely accurate. From the article: "When C was created, it was very fast because it was almost trivial to turn C code into equivalent machine code. But this was only a short-term benefit; in the 30 years since C was created, processors have changed a lot. The task of mapping C code to a modern microprocessor has gradually become increasingly difficult. Since a lot of legacy C code is still around, however, a huge amount of research effort (and money) has been applied to the problem, so we still can get good performance from the language."
Well, we ran our own tests. We took a sizable chunk of supposedly well-written time-critical code that the gang had produced in what was later to become Microsoft C [2] and rewrote the same modules in Logitech Modula-2. The upshot was that the M2 code was measurably faster, smaller, and on examination better optimized. Apparently the C compiler was handicapped by essentially having to figure out what the programmer meant with a long string of low-level expressions.
Extrapolations to today are left to the reader.
[1] I used to comment that C is not a high-level language, which would induce elevated blood pressure in C programmers. After working them up, I'd bet beer money on it -- and then trot out K&R, which contains the exact quote, "C is not a high-level language."
[2] MS originally relabled another company's C complier under license (I forget their name; they were an early object lesson.)
Lacking <sarcasm> tags,
You have two choices when using SIMD instructions in C:
- Use non-portable (between hardware, and often between compilers) intrinsics (or even inline assembly).
- Write non-vectorised code, and hope the compiler can figure out how to optimally decompose these into the intrinsics. Effectively, you think vectorised code, translate it into scalar code, and then expect the compiler to translate it back.
Compare the efficiency of GCC at auto-vectorising FORTRAN (which has a primitive vector type) and C (which doesn't), if you don't believe me.The claim that C cannot inline functions from another source file is also wrong. This is a limitation in gcc, but other compilers can do it, and IIRC the intel compiler can. It is certainly not "impossible".
When you pass a C file to a compiler, it generates an object file. It has absolutely no way of knowing where functions declared in the header are defined. You can hack around this; pass multiple source files to the compiler at once and have it treat them as a single one, for example, but this falls down completely when the function is declared in a library (e.g. libc) and you don't have access to the source.
I am TheRaven on Soylent News
C is faster in the same sense that assembly is faster: You have more control over the resulting machine code, so the code can by definition always be faster. You can optimize by hand. But that comes at a price: You have to optimize by hand. That's why C isn't always faster, especially not when it's supposed to be portable. The question isn't whether there could be a faster program in a language of choice, it's whether a language is at the right level of abstraction for a programmer to describe what the program must do and not a bit more. Overspecification prevents optimization. If you write for (int i=0; i<100; i++) where you really meant for (i in [0..99]), how is the compiler going to know if order is important? The latter is much more easily parallelized, for example. C is full of explicitness where it is often not needed. Assembly even more so. That's the problem of low level languages.
The more abstract a language is, the better a compiler can understand what you are doing. If you write out twenty instructions to do something in a low-level language, it's a lot of work to figure out that what matters isn't that the instructions get executed, but the end result. If you write out one instruction in a high-level language that does the same thing, the compiler can decide how best to get that result without trying to figure out if it's okay to throw away the code you've written. Optimisation is easier and safer.
Furthermore, the bottleneck is often in the programmer's brain rather than the code. If programmers could write code ten times faster, that executes a tenth as quickly, that would actually be a beneficial trade-off for many (most?) organisations. High-level languages help with programmer productivity. I know that it's considered a mark of programmer ability to write the most efficient code possible, but it's a mark of software engineer ability to get the programming done faster while still meeting performance constraints.
Bogtha Bogtha Bogtha
The first mistake: Confusing "compile" performance with execution performance. The job of maping C/C++ code to machine code is trivial.
.NET will make software worse.
I've been programming professionally for over 20 years, and for those 20 years, the argument is that computers are now fast enough to allow high level languages and we don't need those dirty nasty assemblers and low level languages.
What was true 20 years ago is still true today, well written code in a low level language tailored to how the computer actually works will always be faster than a higher level environment.
The problem with computer science today is that the professors are "preaching" a hypothetical computer with no limitations. Suggesting that "real" limitations of computers are somehow unimportant.
If computer science isn't about computers, what is it about? I haate that students coming out of universities, when asked about registers and how would they write a multiply routine if they only had shifts and adds, ask "why do I need to know this?"
Software sucks today because software engineers don't understand computers, and that's why languages and environments like Java and
"I've been programming professionally for over 20 years, and for those 20 years, the argument is that computers are now fast enough to allow high level languages and we don't need those dirty nasty assemblers and low level languages."
.NET will make software worse."
The "appeal to an expert" fallacy?
"What was true 20 years ago is still true today, well written code in a low level language tailored to how the computer actually works will always be faster than a higher level environment."
It also means that portability becomes ever harder, as well as adaptability to new hardware.
"If computer science isn't about computers, what is it about? I haate that students coming out of universities, when asked about registers and how would they write a multiply routine if they only had shifts and adds, ask "why do I need to know this?""
It's about algorithms. Computers just happen to be the most convienent means for trying them..
"The problem with computer science today is that the professors are "preaching" a hypothetical computer with no limitations. Suggesting that "real" limitations of computers are somehow unimportant."
With the trend towards VM's and virtualization, that "hypothetical" computer comes ever closer.
"Software sucks today because software engineers don't understand computers, and that's why languages and environments like Java and
Now who's handwaving?
Whoa! This article seems to be making up history out of whole cloth. I'm not even sure where to begin. It's just totally out to lunch.
:= A + 1) puts it closer, not to PDP-11 architecture, but to contemporary machine architecture in general.
C was not a reaction to LISP. I can't even imagine why anyone would say this. LISP's if/then/else was an influence on ALGOL and later languages.
C might have been a reaction to Pascal, which in turn was a reaction to ALGOL.
LISP was not "the archetypal high-level language." The very names CAR and CDR mean "contents of address register" and "contents of decrement register," direct references to hardware registers on the IBM 704. When the names of fundamental languages constructs are those of specific registers in a specific processor, that is not a "high-level language" at all. Later efforts to build machines with machine architectures optimized for implementation of LISP further show that LISP was not considered "a high-level language."
C was not specifically patterned on the PDP-11. Rather, both of them were based on common practice and understanding of what was in the air at the time. C was a direct successor to, and reasonably similar to BCPL, on Honeywell 635 and 645, the IBM 360, the TX-2, the CDC 6400, the Univac 1108, the PDP-9, the KDF 9 and the Atlas 2.
C makes an interesting comparison with Pascal; you can see that C is, in many ways, a computer language rather than a mathematical language. For example, the inclusion of specific constructs for increment and decrement (as opposed to just writing A
"How to Do Nothing," kids activities, back in print!
From:
Subject: The truth about 'C++' revealed
Date: Tuesday, December 31, 2002 5:20 AM
On the 1st of January, 1998, Bjarne Stroustrup gave an interview to the IEEE's 'Computer' magazine.
Naturally, the editors thought he would be giving a retrospective view of seven years of object-oriented design, using the language he created.
By the end of the interview, the interviewer got more than he had bargained for and, subsequently, the editor decided to suppress its contents, 'for the good of the industry' but, as with many of these things, there was a leak.
Here is a complete transcript of what was was said, unedited, and unrehearsed, so it isn't as neat as planned interviews.
You will find it interesting...
__________________________________________________ ________________
Interviewer: Well, it's been a few years since you changed the world of software design, how does it feel, looking back?
Stroustrup: Actually, I was thinking about those days, just before you arrived. Do you remember? Everyone was writing 'C' and, the trouble was, they were pretty damn good at it. Universities got pretty good at teaching it, too. They were turning out competent - I stress the word 'competent' - graduates at a phenomenal rate. That's what caused the problem.
Interviewer: problem?
Stroustrup: Yes, problem. Remember when everyone wrote Cobol?
Interviewer: Of course, I did too
Stroustrup: Well, in the beginning, these guys were like demi-gods. Their salaries were high, and they were treated like royalty.
Interviewer: Those were the days, eh?
Stroustrup: Right. So what happened? IBM got sick of it, and invested millions in training programmers, till they were a dime a dozen.
Interviewer: That's why I got out. Salaries dropped within a year, to the point where being a journalist actually paid better.
Stroustrup: Exactly. Well, the same happened with 'C' programmers.
Interviewer: I see, but what's the point?
Stroustrup: Well, one day, when I was sitting in my office, I thought of this little scheme, which would redress the balance a little. I thought 'I wonder what would happen, if there were a language so complicated, so difficult to learn, that nobody would ever be able to swamp the market with programmers? Actually, I got some of the ideas from X10, you know, X windows. That was such a bitch of a graphics system, that it only just ran on those Sun 3/60 things. They had all the ingredients for what I wanted. A really ridiculously complex syntax, obscure functions, and pseudo-OO structure. Even now, nobody writes raw X-windows code. Motif is the only way to go if you want to retain your sanity.
[NJW Comment: That explains everything. Most of my thesis work was in raw X-windows. :)]
Interviewer: You're kidding...?
Stroustrup: Not a bit of it. In fact, there was another problem. Unix was written in 'C', which meant that any 'C' programmer could very easily become a systems programmer. Remember what a mainframe systems programmer used to earn?
Interviewer: You bet I do, that's what I used to do.
Stroustrup: OK, so this new language had to divorce itself from Unix, by hiding all the system calls that bound the two together so nicely. This would enable guys who only knew about DOS to earn a decent living too.
Interviewer: I don't believe you said that...
Stroustrup: Well, it's been long enough, now, and I believe most people have figured out for themselves that C++ is a waste of time but, I must say, it's taken them a lot longer than I thought it would.
Interviewer: So how exactly did you do it?
Stroustrup: It was only supposed to be a joke, I never thought people would take the book seriously.