if (any(foo == (/1,2,3,4/)) 而不是 if ((foo == 1).or.(foo == 2).or. ...?

发布于 2025-01-10 00:26:42 字数 571 浏览 0 评论 0原文

我有很多 if 语句，内容类似于

if ((foo == 1).or.(foo == 2).or.(foo == 3).or.(foo == 4)) then
   call bar1
end if
if ((foo == 3).or.(foo == 4).or.(foo == 5).or.(foo == 6)) then
   call bar2
end if

是否有任何理由（速度、风格等）不使用这样的东西？

if (any(foo == (/1,2,3,4/))) call bar1
if (any(foo == (/3,4,5,6/))) call bar2

在我的真实示例中，数字不一定是连续的。所以我不能

if ((foo >= 1).and.(foo <=4)) call bar1
if ((foo >= 3).and.(foo <=6)) call bar1

故意使用两个if条件的重叠，这使得我理解不可能使用SELECT CASE语句。

原文

I have numerous if statements that read something like

if ((foo == 1).or.(foo == 2).or.(foo == 3).or.(foo == 4)) then
   call bar1
end if
if ((foo == 3).or.(foo == 4).or.(foo == 5).or.(foo == 6)) then
   call bar2
end if

Are there any reasons (w.r.t. speed, style, etc.) to not use something like this?

if (any(foo == (/1,2,3,4/))) call bar1
if (any(foo == (/3,4,5,6/))) call bar2

In my real example the numbers are not necessarily sequentially. So I can not use

if ((foo >= 1).and.(foo <=4)) call bar1
if ((foo >= 3).and.(foo <=6)) call bar1

the overlap of the two if conditions is deliberate, which makes it in my understanding impossible to use the SELECT CASE statement.

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浪菊怪哟 2025-01-17 00:26:42

高性能马克已经回答了您的大部分问题，但请允许我提出一个很好的替代方法。

Fortran 允许运算符重载，这允许我们重载.in。 查看某个项目是否在列表中。这个代码看起来像

module in_module
  implicit none
  
  interface operator(.in.)
    module procedure integer_in_integer_list
  end interface
contains
  function integer_in_integer_list(item, list) result(output)
    integer, intent(in) :: item
    integer, intent(in) :: list(:)
    logical :: output
    
    output = any(item==list)
  end function
end module

然后你的代码就变成了

if (foo .in. [1,2,3,4]) call bar1
if (foo .in. [3,4,5,6]) call bar2

在我看来这是最干净的方法，并且它应该具有与其他方法类似的性能。您可以根据需要重载 .in. 以采用其他类型（包括用户定义的类型）。

High Performance Mark has answered most of your question, but allow me to present a nice alternative method.

Fortran allows operator overloading, and this allows us to overload .in. to see if an item is in a list. The code for this would look like

module in_module
  implicit none
  
  interface operator(.in.)
    module procedure integer_in_integer_list
  end interface
contains
  function integer_in_integer_list(item, list) result(output)
    integer, intent(in) :: item
    integer, intent(in) :: list(:)
    logical :: output
    
    output = any(item==list)
  end function
end module

And then your code simply becomes

if (foo .in. [1,2,3,4]) call bar1
if (foo .in. [3,4,5,6]) call bar2

In my opinion this is the cleanest way of doing this, and it should have similar performance to other methods. You can overload .in. to take other types (including user-defined types) as needed.

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