Backport #3297: [patch] Array#pack("i_") is broken in big endian 64bit systems

• Status: Closed
• Assignee: -

[kkaempf (Klaus Kämpf)]

=begin
See also http://redmine.ruby-lang.org/issues/show/1131 for a similar issue (String#unpack("V"))

Array#pack("i_") is broken in big endian 64 bit systems

irb> [1].pack("i_")
=> "\000\000\000\000"

The root cause is similar to the one of issue 1131, use of a wrong offset in a 64bit long.
But the fix is a bit simpler and is probably correct for all other architectures too.

According to the documentation, the "i" format of pack/unpack uses a fixed-size (32bit) integer, while adding "_" uses the system-size.
However, the implementation of Array#pack uses a 'long' type (64bit !) to store an intermediate value, thus breaking OFF() in accessing the wrong 4 bytes of the value.

Fix: Use 'int' to store the intermediate value (use of int is correct for the fixed-size as well as the system-size case) and don't use OFF()

With this patch, the pack_spec and unpack_spec tests of rubyspec.org run without issues.
=end

[akr (Akira Tanaka)]

=begin
OFF* macros are already removed from Ruby 1.8.8.

=end

[shyouhei (Shyouhei Urabe)]

• Status changed from Open to Feedback

Sorry for this late reply, does this still happen? I guess it has already been fixed for a while.

[jeremyevans0 (Jeremy Evans)]

• Status changed from Feedback to Closed