I would love to ignore the 80 bit format, but 4D uses it for VARIABLE TO BLOB, BLOB TO VARIABLE. The goal is to exchange binary data (e.g. large arrays) with another environment and avoid things like converting to and from JSON.
I have at least (mostly) convinced myself the 80 bit “Extended Format” is the x86 extended precision format described in https://en.wikipedia.org/wiki/Extended_precision and not some unknown format tied to the old PPC architecture. The “long double” type in C.
The Racket programming language has direct support for extended floating point numbers. The example below gives the same byte sequence as 4D except for minor variations in the last byte (assumedly because of the higher precision representation in Racket).
(bytes->list (extfl->floating-point-bytes 33.3333t0 #t))
'(64 4 133 85 76 152 95 6 246 148)
REAL TO BLOB($num;$blob;Extended real format)