+/*
+ * According to the letter of standard difference between pointers
+ * is specified to be valid only within same object. This makes
+ * it formally challenging to determine if input and output buffers
+ * are not partially overlapping with standard pointer arithmetic.
+ */
+#ifdef PTRDIFF_T
+# undef PTRDIFF_T
+#endif
+#if defined(OPENSSL_SYS_VMS) && __INITIAL_POINTER_SIZE==64
+/*
+ * Then we have VMS that distinguishes itself by adhering to
+ * sizeof(size_t)==4 even in 64-bit builds, which means that
+ * difference between two pointers might be truncated to 32 bits.
+ * In the context one can even wonder how comparison for
+ * equality is implemented. To be on the safe side we adhere to
+ * PTRDIFF_T even for comparison for equality.
+ */
+# define PTRDIFF_T uint64_t
+#else
+# define PTRDIFF_T size_t
+#endif
+
+int is_partially_overlapping(const void *ptr1, const void *ptr2, int len)
+{
+ PTRDIFF_T diff = (PTRDIFF_T)ptr1-(PTRDIFF_T)ptr2;
+ /*
+ * Check for partially overlapping buffers. [Binary logical
+ * operations are used instead of boolean to minimize number
+ * of conditional branches.]
+ */
+ int overlapped = (len > 0) & (diff != 0) & ((diff < (PTRDIFF_T)len) |
+ (diff > (0 - (PTRDIFF_T)len)));
+
+ return overlapped;
+}
+