fix function ambiguity error in recent Xcode versions

CHANGES.rst

@@ -26,6 +26,9 @@ Bugs fixed
 * C++ exception declarations with mapping functions could fail to compile when
   pre-declared in .pxd files.
 
+* C++ compilation could fail with an ambiguity error in recent MacOS-X Xcode
+  versions.
+
 * C compilation could fail in pypy3.
 
 

Cython/Utility/Buffer.c

@@ -858,16 +858,13 @@ static struct __pyx_typeinfo_string __Pyx_TypeInfoToFormat(__Pyx_TypeInfo *type)
         case 'I':
         case 'U':
             if (size == 1)
-                *buf = 'b';
+                *buf = (type->is_unsigned) ? 'B' : 'b';
             else if (size == 2)
-                *buf = 'h';
+                *buf = (type->is_unsigned) ? 'H' : 'h';
             else if (size == 4)
-                *buf = 'i';
+                *buf = (type->is_unsigned) ? 'I' : 'i';
             else if (size == 8)
-                *buf = 'q';
-
-            if (type->is_unsigned)
-                *buf = toupper(*buf);
+                *buf = (type->is_unsigned) ? 'Q' : 'q';
             break;
         case 'P':
             *buf = 'P';