“real*8"是什么意思?意思是? [英] What does "real*8" mean?

问题描述

用 Fortran 90 编写的程序手册说:所有实变量和参数都以 64 位精度指定(即 real*8)."

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)."

根据Wikipedia，单精度对应32位精度，而双精度对应64 位精度，所以显然程序使用双精度.

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.

但是 real*8 是什么意思呢?

But what does real*8 mean?

我认为 8 的意思是小数点后有 8 位数字.但是，Wikipedia 似乎说单精度通常提供 6-9 位，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?

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?

推荐答案

8指的是数据类型使用的字节数.

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

所以一个 32 位整数是 integer*4 沿着相同的行.

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

快速搜索发现 本 Fortran 数据类型指南，其中包括:

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

real*4"语句将变量名称指定为单精度 4 字节实数，精度为 7 位，幅度范围为 -38 到 +38 的 10.在几乎所有 32 位计算机中，real"语句与real*4"语句相同.

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.

和

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

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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