Unify duplicated helper functions

ref #173

src/memory/client/linux/gneiss-memory-client.adb

@@ -2,6 +2,7 @@
 with System;
 with Gneiss_Internal.Syscall;
 with Gneiss_Internal.Client;
+with Gneiss_Internal.Util;
 with Gneiss_Protocol.Session;
 
 package body Gneiss.Memory.Client with
@@ -16,24 +17,8 @@ is
       External_Name => "gneiss_memfd_create",
       Global        => (In_Out => Gneiss_Internal.Platform_State);
 
-   function Get_First (Length : Integer) return Buffer_Index;
-   function Get_Last (Length : Integer) return Buffer_Index;
-
-   function Get_First (Length : Integer) return Buffer_Index is
-      (if Length < 1 then Buffer_Index'First + 1 else Buffer_Index'First);
-
-   function Get_Last (Length : Integer) return Buffer_Index
-   is
-   begin
-      if Length < 1 then
-         return Buffer_Index'First;
-      end if;
-      if Long_Integer (Length) < Long_Integer (Buffer_Index'Last - Buffer_Index'First + 1) then
-         return Buffer_Index (Long_Integer (Buffer_Index'First) + Long_Integer (Length) - 1);
-      else
-         return Buffer_Index'Last;
-      end if;
-   end Get_Last;
+   function Get_First is new Gneiss_Internal.Util.Get_First (Buffer_Index);
+   function Get_Last is new Gneiss_Internal.Util.Get_Last (Buffer_Index);
 
    procedure Initialize (Session : in out Client_Session;
                          Cap     :        Capability;

src/memory/server/linux/gneiss-memory-server.adb

@@ -1,28 +1,13 @@
 
 with Gneiss_Internal.Syscall;
+with Gneiss_Internal.Util;
 
 package body Gneiss.Memory.Server with
    SPARK_Mode
 is
 
-   function Get_First (Length : Integer) return Buffer_Index;
-   function Get_Last (Length : Integer) return Buffer_Index;
-
-   function Get_First (Length : Integer) return Buffer_Index is
-      (if Length < 1 then Buffer_Index'First + 1 else Buffer_Index'First);
-
-   function Get_Last (Length : Integer) return Buffer_Index
-   is
-   begin
-      if Length < 1 then
-         return Buffer_Index'First;
-      end if;
-      if Long_Integer (Length) < Long_Integer (Buffer_Index'Last - Buffer_Index'First + 1) then
-         return Buffer_Index (Long_Integer (Buffer_Index'First) + Long_Integer (Length) - 1);
-      else
-         return Buffer_Index'Last;
-      end if;
-   end Get_Last;
+   function Get_First is new Gneiss_Internal.Util.Get_First (Buffer_Index);
+   function Get_Last is new Gneiss_Internal.Util.Get_Last (Buffer_Index);
 
    procedure Modify (Session : in out Server_Session;
                      Ctx     : in out Context)

src/platform/linux/gneiss_internal-util.adb

@@ -0,0 +1,22 @@
+
+package body Gneiss_Internal.Util with
+   SPARK_Mode
+is
+
+   function Get_First (Length : Integer) return Buffer_Index is
+      (if Length < 1 then Buffer_Index'First + 1 else Buffer_Index'First);
+
+   function Get_Last (Length : Integer) return Buffer_Index
+   is
+   begin
+      if Length < 1 then
+         return Buffer_Index'First;
+      end if;
+      if Long_Integer (Length) < Long_Integer (Buffer_Index'Last - Buffer_Index'First + 1) then
+         return Buffer_Index (Long_Integer (Buffer_Index'First) + Long_Integer (Length) - 1);
+      else
+         return Buffer_Index'Last;
+      end if;
+   end Get_Last;
+
+end Gneiss_Internal.Util;

src/platform/linux/gneiss_internal-util.ads

@@ -0,0 +1,14 @@
+
+package Gneiss_Internal.Util with
+   SPARK_Mode
+is
+
+   generic
+      type Buffer_Index is range <>;
+   function Get_First (Length : Integer) return Buffer_Index;
+
+   generic
+      type Buffer_Index is range <>;
+   function Get_Last (Length : Integer) return Buffer_Index;
+
+end Gneiss_Internal.Util;

src/rom/client/linux/gneiss-rom-client.adb

@@ -2,30 +2,15 @@
 with System;
 with Gneiss_Internal.Syscall;
 with Gneiss_Internal.Client;
+with Gneiss_Internal.Util;
 with Gneiss_Protocol.Session;
 
 package body Gneiss.Rom.Client with
    SPARK_Mode
 is
 
-   function Get_First (Length : Integer) return Buffer_Index;
-   function Get_Last (Length : Integer) return Buffer_Index;
-
-   function Get_First (Length : Integer) return Buffer_Index is
-      (if Length < 1 then Buffer_Index'First + 1 else Buffer_Index'First);
-
-   function Get_Last (Length : Integer) return Buffer_Index
-   is
-   begin
-      if Length < 1 then
-         return Buffer_Index'First;
-      end if;
-      if Long_Integer (Length) < Long_Integer (Buffer_Index'Last - Buffer_Index'First + 1) then
-         return Buffer_Index (Long_Integer (Buffer_Index'First) + Long_Integer (Length) - 1);
-      else
-         return Buffer_Index'Last;
-      end if;
-   end Get_Last;
+   function Get_First is new Gneiss_Internal.Util.Get_First (Buffer_Index);
+   function Get_Last is new Gneiss_Internal.Util.Get_Last (Buffer_Index);
 
    procedure Initialize (Session : in out Client_Session;
                          Cap     :        Gneiss.Capability;