Document Lisp floats a bit better

* doc/lispref/numbers.texi (Float Basics):
* doc/misc/cl.texi (Implementation Parameters):
* lisp/emacs-lisp/cl-lib.el (cl-most-positive-float)
(cl-least-positive-float)
(cl-least-positive-normalized-float, cl-float-epsilon)
(cl-float-negative-epsilon):
Document IEEE floating point better.  Don’t suggest that Emacs
might use some floating-point format other than IEEE format, as
Emacs currently assumes IEEE in several places and there seems
little point in removing those assumptions.

1 files changed, 7 insertions, 9 deletions

diff --git a/lisp/emacs-lisp/cl-lib.el b/lisp/emacs-lisp/cl-lib.el
index ff096918173..7d0df27e14b 100644
--- a/lisp/emacs-lisp/cl-lib.el
+++ b/lisp/emacs-lisp/cl-lib.el
@@ -299,7 +299,7 @@ If true return the decimal value of digit CHAR in RADIX."
 (defconst cl-most-positive-float nil
   "The largest value that a Lisp float can hold.
 If your system supports infinities, this is the largest finite value.
-For IEEE machines, this is approximately 1.79e+308.
+For Emacs, this equals 1.7976931348623157e+308.
 Call `cl-float-limits' to set this.")
 
 (defconst cl-most-negative-float nil
@@ -309,8 +309,8 @@ Call `cl-float-limits' to set this.")
 
 (defconst cl-least-positive-float nil
   "The smallest value greater than zero that a Lisp float can hold.
-For IEEE machines, it is about 4.94e-324 if denormals are supported,
-or 2.22e-308 if they are not.
+For Emacs, this equals 5e-324 if subnormal numbers are supported,
+`cl-least-positive-normalized-float' if they are not.
 Call `cl-float-limits' to set this.")
 
 (defconst cl-least-negative-float nil
@@ -320,10 +320,8 @@ Call `cl-float-limits' to set this.")
 
 (defconst cl-least-positive-normalized-float nil
   "The smallest normalized Lisp float greater than zero.
-This is the smallest value for which IEEE denormalization does not lose
-precision.  For IEEE machines, this value is about 2.22e-308.
-For machines that do not support the concept of denormalization
-and gradual underflow, this constant equals `cl-least-positive-float'.
+This is the smallest value that has full precision.
+For Emacs, this equals 2.2250738585072014e-308.
 Call `cl-float-limits' to set this.")
 
 (defconst cl-least-negative-normalized-float nil
@@ -334,12 +332,12 @@ Call `cl-float-limits' to set this.")
 (defconst cl-float-epsilon nil
   "The smallest positive float that adds to 1.0 to give a distinct value.
 Adding a number less than this to 1.0 returns 1.0 due to roundoff.
-For IEEE machines, epsilon is about 2.22e-16.
+For Emacs, this equals 2.220446049250313e-16.
 Call `cl-float-limits' to set this.")
 
 (defconst cl-float-negative-epsilon nil
   "The smallest positive float that subtracts from 1.0 to give a distinct value.
-For IEEE machines, it is about 1.11e-16.
+For Emacs, this equals 1.1102230246251565e-16.
 Call `cl-float-limits' to set this.")