According to the specification, if M < 0, the tape is skipped backwards M blocks, or to the beginning of the tape, whichever comes first.  In the implementation, we don't check to verify that we aren't seeking past the beginning of the file. This causes fseek(3) to fail, and it leaves us at the position we were at.

I have attached a demo of this as mixal source, and a simple patch that causes the tape to rewind correctly.

Summary of changes:
-      if (m == 0) rewind (file);
+      if (m == 0 || (ftell (file) + m <= 0 )) rewind (file);


-Kevin Brunelle