Document the undefinedness of bitshifting out of range.

p4raw-id: //depot/perl@10006

diff --git a/pod/perlop.pod b/pod/perlop.pod
index 5cfdb4a..ec96f04 100644 (file)
--- a/pod/perlop.pod
+++ b/pod/perlop.pod
@@ -233,6 +233,18 @@ Binary ">>" returns the value of its left argument shifted right by
 the number of bits specified by the right argument.  Arguments should
 be integers.  (See also L<Integer Arithmetic>.)
 
+Note that both "<<" and ">>" in Perl are implemented directly using
+"<<" and ">>" in C.  If C<use integer> (see L<Integer Arithmetic>) is
+in force then signed C integers are used, else unsigned C integers are
+used.  Either way, the implementation isn't going to generate results
+larger than the size of the integer type Perl was built with (32 bits
+or 64 bits).
+
+The result of overflowing the range of the integers is undefined
+because it is undefined also in C.  In other words, using 32-bit
+integers, C<< 1 << 32 >> is undefined.  Shifting by a negative number
+of bits is also undefined.
+
 =head2 Named Unary Operators
 
 The various named unary operators are treated as functions with one