A quick google turned this up for double precison format dunno about extended though
Floating point Numbers
For packing floating point numbers you have the choice between the pack codes f and d which pack into (or unpack from) single-precision or double-precision representation as it is provided by your system. (There is no such thing as a network representation for reals, so if you want to send your real numbers across computer boundaries, you'd better stick to ASCII representation, unless you're absolutely sure what's on the other end of the line.)
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