See the pack templates, especially V, N and F and D. Also, F and D are hardware specific and will not port between architectures. BrowserUk wrote IEEE 754 80-bit Extended double (long double) to 64-bit double unpack and IEEE 754 64-bit double to 80-bit Extended double (long double) pack (Updated). to manually unpack (IEEE) floating point values.

Internally, Perl does not know about endianness, so you only have to worry converting on input and output of such values.