[glib: 1/2] gtypes: Define signed integer minimum values in terms of maximum values

[Philip Withnall <pwithnall src gnome org>]

commit 6a2cfde29ffb442daa944a4a109991f21d12bfc6
Author: Philip Withnall <withnall endlessm com>
Date:   Wed Jan 23 13:07:44 2019 +0000

    gtypes: Define signed integer minimum values in terms of maximum values
    
    This is what limits.h does. It avoids a problem when compiling with MSVC
    (in C++ mode) on Windows, whereby the 0x80000000 constant is interpreted
    as unsigned, and *then* the unary minus is applied to it.
    
    
https://docs.microsoft.com/en-us/cpp/error-messages/compiler-warnings/compiler-warning-level-2-c4146?view=vs-2017
    
    Add a test which should hopefully catch problems with different
    compilers’ interpretations of this in future.
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://gitlab.gnome.org/GNOME/glib/issues/1663

 glib/gtypes.h      |  8 ++++----
 glib/tests/utils.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+), 4 deletions(-)
---
diff --git a/glib/gtypes.h b/glib/gtypes.h
index 67adb7f1f..f5b369dc5 100644
--- a/glib/gtypes.h
+++ b/glib/gtypes.h
@@ -58,19 +58,19 @@ typedef float   gfloat;
 typedef double  gdouble;
 
 /* Define min and max constants for the fixed size numerical types */
-#define G_MININT8      ((gint8) -0x80)
+#define G_MININT8      ((gint8) (-G_MAXINT8 - 1))
 #define G_MAXINT8      ((gint8)  0x7f)
 #define G_MAXUINT8     ((guint8) 0xff)
 
-#define G_MININT16     ((gint16) -0x8000)
+#define G_MININT16     ((gint16) (-G_MAXINT16 - 1))
 #define G_MAXINT16     ((gint16)  0x7fff)
 #define G_MAXUINT16    ((guint16) 0xffff)
 
-#define G_MININT32     ((gint32) -0x80000000)
+#define G_MININT32     ((gint32) (-G_MAXINT32 - 1))
 #define G_MAXINT32     ((gint32)  0x7fffffff)
 #define G_MAXUINT32    ((guint32) 0xffffffff)
 
-#define G_MININT64     ((gint64) G_GINT64_CONSTANT(-0x8000000000000000))
+#define G_MININT64     ((gint64) (-G_MAXINT64 - G_GINT64_CONSTANT(1)))
 #define G_MAXINT64     G_GINT64_CONSTANT(0x7fffffffffffffff)
 #define G_MAXUINT64    G_GUINT64_CONSTANT(0xffffffffffffffff)
 
diff --git a/glib/tests/utils.c b/glib/tests/utils.c
index 79bc08184..421a70560 100644
--- a/glib/tests/utils.c
+++ b/glib/tests/utils.c
@@ -655,6 +655,36 @@ test_check_setuid (void)
   g_assert (!res);
 }
 
+/* Test the defined integer limits are correct, as some compilers have had
+ * problems with signed/unsigned conversion in the past. These limits should not
+ * vary between platforms, compilers or architectures.
+ *
+ * Use string comparisons to avoid the same systematic problems with unary minus
+ * application in C++. See https://gitlab.gnome.org/GNOME/glib/issues/1663. */
+static void
+test_int_limits (void)
+{
+  gchar *str = NULL;
+
+  g_test_bug ("https://gitlab.gnome.org/GNOME/glib/issues/1663";);
+
+  str = g_strdup_printf ("%d %d %u\n"
+                         "%" G_GINT16_FORMAT " %" G_GINT16_FORMAT " %" G_GUINT16_FORMAT "\n"
+                         "%" G_GINT32_FORMAT " %" G_GINT32_FORMAT " %" G_GUINT32_FORMAT "\n"
+                         "%" G_GINT64_FORMAT " %" G_GINT64_FORMAT " %" G_GUINT64_FORMAT "\n",
+                         G_MININT8, G_MAXINT8, G_MAXUINT8,
+                         G_MININT16, G_MAXINT16, G_MAXUINT16,
+                         G_MININT32, G_MAXINT32, G_MAXUINT32,
+                         G_MININT64, G_MAXINT64, G_MAXUINT64);
+
+  g_assert_cmpstr (str, ==,
+                   "-128 127 255\n"
+                   "-32768 32767 65535\n"
+                   "-2147483648 2147483647 4294967295\n"
+                   "-9223372036854775808 9223372036854775807 18446744073709551615\n");
+  g_free (str);
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -706,6 +736,7 @@ main (int   argc,
   g_test_add_func ("/utils/nullify", test_nullify);
   g_test_add_func ("/utils/atexit", test_atexit);
   g_test_add_func ("/utils/check-setuid", test_check_setuid);
+  g_test_add_func ("/utils/int-limits", test_int_limits);
 
   return g_test_run ();
 }