add GDIT's performance optimization for RRFS

src/gsi/crc32.F90

@@ -0,0 +1,23 @@
+module crc32
+  use iso_c_binding
+  implicit none
+  public :: digest
+
+  interface
+    integer function digest_c(message) bind(c)
+      use iso_c_binding, only: c_char
+      character(kind=c_char), intent(in) :: message(*)
+    end function digest_c
+  end interface
+
+  contains
+
+  integer function digest(m)
+    use iso_c_binding, only: c_null_char
+    implicit none
+    character(len=*), intent(in) :: m
+    !m='nid001019'
+    digest=abs(digest_c(trim(m)//c_null_char))
+    !write(6,'("Digest ",I12)') digest
+  end function digest
+end module crc32

src/gsi/crc32_c.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include <string.h>
+#include <zlib.h>
+
+uLong digest_c(char * message) {
+  return crc32(0, (const void*)message, strlen(message));
+}