Add support for GNU Fortran 15.1. Fix unsigned functions.

Author: interkosmos

README.md

@@ -1,6 +1,8 @@
 # fortran-unix
 
-[![Build](https://github.com/interkosmos/fortran-unix/actions/workflows/build.yml/badge.svg)](https://github.com/interkosmos/fortran-unix/actions/workflows/build.yml)
+![Language](https://img.shields.io/badge/-Fortran-734f96?logo=fortran&logoColor=white)
+![License](https://img.shields.io/github/license/dabamos/dmpack?color=blue)
+![Build](https://github.com/interkosmos/fortran-unix/actions/workflows/build.yml/badge.svg)
 
 A work-in-progress collection of Fortran 2008 ISO C binding interfaces to
 selected POSIX and SysV types, functions, and routines on 64-bit Unix-like

src/unix.f90

@@ -95,7 +95,7 @@ pure elemental function c_uint16_to_int32(u) result(s)
         integer(kind=c_uint16_t), intent(in) :: u !! Unsigned integer.
         integer(kind=c_int32_t)              :: s !! Signed integer.
 
-        if (u > 0) then
+        if (u >= 0) then
             s = int(u, kind=c_int32_t)
         else
             s = 65536_c_int32_t + int(u, kind=c_int32_t)
@@ -107,7 +107,7 @@ pure elemental function c_uint32_to_int64(u) result(s)
         integer(kind=c_uint32_t), intent(in) :: u !! Unsigned integer.
         integer(kind=c_int64_t)              :: s !! Signed integer.
 
-        if (u > 0) then
+        if (u >= 0) then
             s = int(u, kind=c_int64_t)
         else
             s = 4294967296_c_int64_t + int(u, kind=c_int64_t)

src/unix_types.F90

@@ -7,7 +7,7 @@ module unix_types
     implicit none
     private
 
-#if defined (__flang__)
+#if defined (__flang__) || (defined (__GFORTRAN__) && __GNUC__ >= 15 && __GNUC_MINOR__ >= 1)
 
     public :: c_uint16_t
     public :: c_uint32_t