ICU-827 Move U_MAX_PTR from utypes.h to putil.h because it's a private platform macro

X-SVN-Rev: 4291

icu4c/source/common/unicode/putil.h

@@ -291,4 +291,24 @@ u_getVersion(UVersionInfo versionArray);
 #   error Unknown charset family!
 #endif
 
+/**
+ * Maximum value of a (void*) - use to indicate the limit of an 'infinite' buffer.
+ * In fact, buffer sizes must not exceed 2GB so that the difference between
+ * the buffer limit and the buffer start can be expressed in an int32_t.
+ *
+ * The definition of U_MAX_PTR must fulfill the following conditions:
+ * - return the largest possible pointer greater than base
+ * - return a valid pointer according to the machine architecture (AS/400, 64-bit, etc.)
+ * - avoid wrapping around at high addresses
+ * - make sure that the returned pointer is not farther from base than 0x7fffffff
+ *
+ * For some architectures (like AS/400), a custom macro must be defined in platform.h.in or similar.
+ *
+ * @param base The beginning of a buffer to find the maximum offset from
+ * @internal
+ */
+#ifndef U_MAX_PTR
+#   define U_MAX_PTR(base) ((void *)(((char *)(base)+0x7fffffff)>(char *)(base) ? ((char *)(base)+0x7fffffff) : (char *)-1))
+#endif
+
 #endif