From ...
From: Erik Naggum <erik@naggum.no>
Subject: Re: why no big-float?
Date: 1996/04/09
Message-ID: <3038075592819373@arcana.naggum.no>#1/1
X-Deja-AN: 146611694
references: <-0904960524410001@mac1.yost.com>
organization: Naggum Software; +47 2295 0313
newsgroups: comp.lang.lisp,comp.lang.lisp.mcl

[Dave Yost]

|   We have bignum.  Why don't we have big-float?
:
|   Has anyone implemented big-float?

CLISP has this.

$ clisp

> (list (lisp-implementation-type) (lisp-implementation-version))
("CLISP" "1996-03-15 (March 1996)")
> (/ 7l0)
0.14285714285714285714L0
> (float-digits *)
64
> (setf (long-float-digits) 128)
128
> (/ 7l0)
0.142857142857142857142857142857142857143L0
> (float-digits *)
128
> (quit)

it is not exactly well documented, but pretty much what you outlined.

#<Erik>
-- 
education is for people who can't handle reality the hard way