在 Fortran 中混淆双精度实数 [英] Confusing double precision real in Fortran

问题描述

我现在有一个紧迫的问题:在现代 Fortran 中声明双精度实数的公认"方式是什么?按照从最旧到最新的顺序，故事似乎是这样的:DOUBLE PRECISION，然后是 REAL(kind=8)，然后是 INTEGER, PARAMETER :: dp=kind(1.d0) 和 REAL(kind=dp)--Metcalf 现在说 dp=kind(0.d0)--现在 float32=selected_real_kind(6,37) 或 float64=selected_real_kind(15,307).所以...

Have this burning question on my mind right now: What is the "accepted" way to declare double precision real in modern Fortran? In order from oldest to newest, the story seems to go like this: DOUBLE PRECISION, then REAL(kind=8), then INTEGER, PARAMETER :: dp=kind(1.d0) with REAL(kind=dp)--Metcalf now says dp=kind(0.d0)--and now float32=selected_real_kind(6,37) or float64=selected_real_kind(15,307). So...

1. 我现在应该如何声明双精度真实?
2. 在 REAL(kind=dp) 中 kind 是多余的吗?
3. 在编译时是否需要任何特殊标志来使用 gfortran 或 ifort 调用双精度实数?

1. How should I be declaring double precision real now?
2. Is kind redundant in REAL(kind=dp)?
3. Are there any special flags needed at compile time to invoke double precision real with gfortran or ifort?

推荐答案

我个人现在写

use, intrinsic :: iso_fortran_env

其中包含int32、real64等参数，含义很明显，可以这样使用:

which includes parameters such as int32,real64 which have the obvious meanings, and can be used like this:

real(real64) :: a_64_bit_real_scalar

请注意，标准不保证 kind=8 提供 8 字节的种类.kind 参数采用的值不是标准化的，并且因编译器而异.

Note that kind=8 is not guaranteed, by the standard, to deliver an 8-byte kind. The values that kind parameters take are not standardised and do vary from compiler to compiler.

如果需要，您可以编写诸如

You could, if you want, write statements such as

use, intrinsic :: iso_fortran_env, dp=>real64
...
real(dp) :: a_64_bit_real_scalar

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