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

Fortran traditionally doesn't set options such as -fp:strict (which ifort requires to enable some of the features in USE IEEE_arithmetic, a part of f2003 standard). Intel C++ also doesn't set -fp:strict as a default, but that is required for ERRNO handling, for example, and other C++ compilers don't make it convenient to turn off ERRNO or gain optimizations such as simd reduction. gcc and g++ have required me to set up Makefile to avoid using the dangerous combination -O3 -ffast-math -fopenmp -march=native. Other than these issues, this question about relative performance gets more nit-picky and dependent on local rules about choice of compilers and options.

其他回答

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。

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。

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。

Fortran速度更快有几个原因。然而,它们的重要性是如此无关紧要,或者可以通过任何方式解决,所以它不应该是重要的。现在使用Fortran的主要原因是维护或扩展遗留应用程序。

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 language. 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() 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 Builtin complex type. In theory this could allow the compiler to reorder or eliminate certain instructions in certain cases, but likely you'd see the same benefit with the struct { double re; double im; }; idiom used in C. It makes for faster development though as operators work on complex types in Fortran.

Fortran可以非常方便地处理数组,特别是多维数组。在Fortran中对多维数组元素进行切片比在C/ c++中容易得多。c++现在有库可以做这项工作,比如Boost或Eigen,但它们毕竟是外部库。在Fortran中,这些函数是固有的。

对于开发来说,Fortran是更快还是更方便主要取决于您需要完成的工作。作为地球物理的科学计算人员,我用Fortran(我指的是现代Fortran, >=F90)进行了大部分计算。