我不时地读到Fortran在繁重的计算中比C更快。这是真的吗?我必须承认我几乎不懂Fortran,但是到目前为止我看到的Fortran代码并没有显示出该语言具有C语言所不具备的特性。

如果是真的,请告诉我原因。请不要告诉我什么语言或库适合处理数字,我不打算写一个应用程序或库来做这个,我只是好奇。


当前回答

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. Which makes it easier to compile for certain types of algorithms especially for parallel machines.

在运行时系统和调用约定等方面,C语言和现代的Fortran非常相似,很难看出有什么不同。注意,这里的C实际上是基础C: c++是一个完全不同的问题,具有非常不同的性能特征。

其他回答

I was doing some extensive mathematics with FORTRAN and C for a couple of years. From my own experience I can tell that FORTRAN is sometimes really better than C but not for its speed (one can make C perform as fast as FORTRAN by using appropriate coding style) but rather because of very well optimized libraries like LAPACK (which can, however, be called from C code as well, either linking against LAPACK directly or using the LAPACKE interface for C), and because of great parallelization. On my opinion, FORTRAN is really awkward to work with, and its advantages are not good enough to cancel that drawback, so now I am using C+GSL to do calculations.

我将Fortran、C和c++的速度与netlib中的经典Levine-Callahan-Dongarra基准进行了比较。使用OpenMP的多语言版本是 http://sites.google.com/site/tprincesite/levine-callahan-dongarra-vectors C语言更丑陋,因为它一开始是自动翻译,加上某些编译器的限制和pragmas插入。 c++就是在适用的地方使用STL模板的C。在我看来,STL在是否能提高可维护性方面好坏参半。

为了了解自动函数内联在多大程度上改进了优化,只需要进行很少的练习,因为示例基于传统的Fortran实践,其中很少依赖内联。

到目前为止使用最广泛的C/ c++编译器缺乏自动向量化,而这些基准测试严重依赖于此。

关于这之前的帖子:在Fortran中使用括号来指示更快或更准确的求值顺序的例子有两个。已知的C编译器没有在不禁用更重要的优化的情况下观察括号的选项。

使用现代标准和编译器,不!

Some of the folks here have suggested that FORTRAN is faster because the compiler doesn't need to worry about aliasing (and hence can make more assumptions during optimisation). However, this has been dealt with in C since the C99 (I think) standard with the inclusion of the restrict keyword. Which basically tells the compiler, that within a give scope, the pointer is not aliased. Furthermore C enables proper pointer arithmetic, where things like aliasing can be very useful in terms of performance and resource allocation. Although I think more recent version of FORTRAN enable the use of "proper" pointers.

对于现代实现,C通用优于FORTRAN(尽管它也非常快)。

http://benchmarksgame.alioth.debian.org/u64q/fortran.html

编辑:

一个公平的批评似乎是,基准测试可能是有偏见的。这里是另一个来源(相对于C),将结果放在更多的上下文中:

http://julialang.org/benchmarks/

你可以看到C在大多数情况下优于Fortran(再次看到下面的批评也适用于这里);正如其他人所指出的,基准测试是一门不精确的科学,很容易偏袒一种语言而不是其他语言。但它确实说明了Fortran和C语言有相似的性能。

This is more than somewhat subjective, because it gets into the quality of compilers and such more than anything else. However, to more directly answer your question, speaking from a language/compiler standpoint there is nothing about Fortran over C that is going to make it inherently faster or better than C. If you are doing heavy math operations, it will come down to the quality of the compiler, the skill of the programmer in each language and the intrinsic math support libraries that support those operations to ultimately determine which is going to be faster for a given implementation.

编辑:@Nils等人提出了一个很好的观点,即C语言中指针使用的差异,以及可能存在的别名,这可能会使C语言中最简单的实现变慢。然而,在C99中有一些方法可以解决这个问题,比如通过编译器优化标志和/或C语言的实际编写方式。这在@Nils的回答和随后的评论中有很好的介绍。

Fortran有更好的I/O例程,例如隐含的do工具提供了C标准库无法比拟的灵活性。

Fortran编译器直接处理更复杂的 涉及到语法,而且这样的语法不能轻易简化 参数传递形式,C不能有效地实现它。