什么是“真实* 8”意思？ [英] What does "real*8" mean?

问题描述

用Fortran 90编写的程序手册说：所有的实际变量和参数都是以64位精度指定的（即 real * 8 ）。

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根据 Wikipedia ，单精度对应到32位精度，而双精度对应于64位精度，所以程序显然使用双精度。

但 real * 8 是什么意思？

我认为 8 意味着8位数字在小数点后面。然而，维基百科似乎表示，单精度通常提供6-9位数，而双精度通常提供15-17位数字。这是否意味着64位精度语句与 real * 8 不一致？

解决方案

8表示数据类型使用的字节数。

所以，一个32位整数是整数* 4 沿着同一行。

快速搜索发现 Fortran数据类型指南，其中包括：
$ b

real * 4语句将变量名称指定为单精度4字节实数，具有7个数字的精度和从-38到+38的10的幅度范围。几乎所有32位计算机的真实声明都与真实* 4声明相同。

和

real * 8语句将变量名称指定为双精度8字节实数，其精度为15位，幅度范围为10从-308到+308。在几乎所有的32位计算机中，double precision语句与real * 8语句相同。

The manual of a program written in Fortran 90 says, "All real variables and parameters are specified in 64-bit precision (i.e. real*8)."

According to Wikipedia, single precision corresponds to 32-bit precision, whereas double precision corresponds to 64-bit precision, so apparently the program uses double precision.

But what does real*8 mean?

I thought that the 8 meant that 8 digits follow the decimal point. However, Wikipedia seems to say that single precision typically provides 6-9 digits whereas double precision typically provides 15-17 digits. Does this mean that the statement "64-bit precision" is inconsistent with real*8?

解决方案

The 8 refers to the number of bytes that the data type uses.

So a 32-bit integer is integer*4 along the same lines.

A quick search found this guide to Fortran data types, which includes:

The "real*4" statement specifies the variable names to be single precision 4-byte real numbers which has 7 digits of accuracy and a magnitude range of 10 from -38 to +38. The "real" statement is the same as "real*4" statement in nearly all 32-bit computers.

and

The "real*8" statement specifies the variable names to be double precision 8-byte real numbers which has 15 digits of accuracy and a magnitude range of 10 from -308 to +308. The "double precision" statement is the same as "real*8" statement in nearly all 32-bit computers.

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