literal-kind-suffix (PORT012)

This rule is turned on by default.

What it does

Checks for using an integer literal as a kind suffix

Why is this bad?

Using an integer literal as a kind specifier gives no guarantees regarding the precision of the type, as kind numbers are not specified in the Fortran standards. It is recommended to use parameter types from iso_fortran_env:

use, intrinsic :: iso_fortran_env, only: sp => real32, dp => real64

or alternatively:

integer, parameter :: sp => selected_real_kind(6, 37)
integer, parameter :: dp => selected_real_kind(15, 307)

Floating point constants can then be specified as follows:

real(sp), parameter :: sqrt2 = 1.41421_sp
real(dp), parameter :: pi = 3.14159265358979_dp