Is Fortran faster than C
The languages have similar feature set. The performance difference comes from the fact that fpatagonia better sweater beanie large3ortran says aliasing is not allowed. Any code that has aliasing is not valid fortran but it is up to the programmer and not the compiler to detect these errors. Thus fortran compilers ignore possible aliasing of memory pointers and allows them to genepatagonia better sweater feather greyrate more efficient code. Take a look at this little example in C:
void transform (float output, float const input, float const matrix, int n)This function would run slower than the fortran counterpart after optimization. Why so? If you write values into the output array you may change the values of matrix. After all the pointers could overlap and point to the same chunk of memory (including the int pointer!). The C compiler is forced to reload the four matrix values from memory for all computations.
In fortran the compiler can load the matrix values once and store them in registers. It can do so becapatagonia better sweater beanie largeuse the fortran compiler assumes pointers/arrays do not overlap in memory.
Fortunately the restrict keyword and strict aliasing have been introduced to the C99 standard to address this problem. It s well supported in most C++ compilers these days as well. The keyword allows you to give the compiler a hint that the programmer promises that a pointer does not alias with any other pointer. The strict aliasing means that the programmer promises that pointers of different type will never overlap, for example a double will not overlap with an int (with the specific exception that char and void can overlap with anything).
If you use them you will get the same patagonia tour companies reviewsspeed from C and Fortran. However, the ability to use the restrict keyword only with performance critical functions means that C (and C++) programs are much safer and easier to write. For example, consider the invalid fortran CALL TRANSFORM(A(1,30),A(2,31),A(3,32),30) which most fortran compilers will happily compile without any warning but introduces a bug that only shows up on some compilers, on some hardware and with some optimization options.
Yes, in 1980; in 2008? depends
When I started programming professionally the speed dominance of Fortran was just being challenged. I remember reading about it in Dr. Dobbs and telling the patagonia mixed guide pants ukolder programmers about the article they laughed.
So I have two views about this, theoretical and practical. In theory Fortran today has no intrinsic advantage to C/C++ or even any language that allows assembly code. In practice Fortran today still enjoys the benefits of legacy of a history and culture built around optimization of numerical code.
Up until and including Fortran 77, language design considepatagonia boots for salerations had optimization as a main focus. Due to the state of compiler theory and technology, this often meant restricting features and capability in order patagonia messenger bag reviewto give the compiler the best shot at optimizing the code. A good analogy is to think of Fortran 77 as a professional race car that sacrifices features for speed. These days compilers have gotten better across all languages and features for programmer productivity are more valued. However, there are still places where the people are mainly concerned with speed in scientific computing; these people most likely have inherited code, training and culture from people who themselves were Fortran programmers.
When one starts talking about optimization of code there are many issues and the best way to get a feel for this is to lurk where people are whose job it is to have fast numerical code. But keep in mind that such critically sensitive code is usually a small fraction of the overall lines of code and very specialized: A lot of Fortran code is just as inefficient as a lot of other code in other languages and optimization should not even be a primary concern of such code.
A wonderful place to start in learning about the history apatagonia outlet store 3462nd culture of Fortran is wikipedia. The Fortran Wikipedia entry is superb and I very much appreciate those who have taken the time and effort to make it of value for the Fortran community.
(A shortened version of this answer would have been a comment in the excellent thread stapatagonia austin new churchrted by Nils but I don t have the karma to do that. Actually, I probably wouldn t have written anything at all but for that this thread has actual information content and sharing as opposed to flame wars and language bigotry, which is my main experience with this patagonia better sweater beanie large0subject. I was overwhelmed and had to share the love.)
To some extent Fortran has been designed keeping compiler optimization in mind. The language supports whole array operations where compilers can exploit parallelism (specially on multi core processors). For example,
Dense matrix multiplication is simply:L2 norm of a vector x is:Moreover statements such as FORALL, PURE ELEMENTAL procedures etc. further help to optimize code. Even pointers in Fortran arent as flexible as C because of this simple reason.
The upcoming Fortran standard (2008) has co arrays which allows you to easily write parallel code. G95 (open source) and compilers from CRAY already support it.
So yes Fortran can be fast simply because compilers can optimize/parallelize it better than C/C++. But again like everything else in life there are good compilers and bad compilers.
I think the key point in favor of Fortran is that it is a language slightly more suited for expressing vector and array based math. The pointer analysis issue pointed out above is real in practice, since portable code cannot really assume that you can tell a compiler something. There is ALWAYS an advantage to expression computaitons in a manner closer to how the domain looks. C does not really have arrays at all, if you look closely, just something that kind of behaves like it. Fortran has real arrawys. Whipatagonia guide jacket blousech makes it easier to compile for certain types of algorithms especially for parallel machines.
Deep down in things like run time system and calling conventions, C and modern Fortran are sufficiently similar that it is hard to see what would make a difference. patagonia guide jacket of withstandingNote that C here is really base C: C++ is a totally different issue with very different performance characteristics.
There are several reasons why Fortran could be faster. However the amount they matter is so inconsequential or can be worked around anyways, that it shouldn t matter. The main reason to use Fortran nowadays is maintaining or extending legacy applications.
PURE and ELEMENTAL keywords on functions. These are functions that have no side effects. This allows optimizations in certain cases where the compiler knows the same function will be called with the same values. Note: GCC implements pure as an extension to the languapatagonia better sweater beanie large2ge. Other compilers may as well. Inter module analysis can also perform this optimization but it is difficult.
standard set of functions that deal with arrays, not individual elements. Stuff like sin(), log(), sqrt()patagonia better sweater beanie large1 take arrays instead of scalars. This makes it easier to optimize the routine. Auto vectorization gives the same benefits in most cases if these functions are inline or builtins
