22.1.50; calc-math.el patch: fix non-termination

[Markus Triska]

With the OS I'm currently working on, the result of (expt 10.0 x) is
1.0e+INF for x >= 309, i.e., no range error is triggered. This patch
to calc-math.el prevents non-termination when loading the file.

2007-09-26  Markus Triska  <address@hidden>

        * calc/calc-math.el (math-largest-emacs-expt)
        (math-smallest-emacs-expt): more robust computation

diff --git a/lisp/calc/calc-math.el b/lisp/calc/calc-math.el
index 3e4743d..44ccbcc 100644
--- a/lisp/calc/calc-math.el
+++ b/lisp/calc/calc-math.el
@@ -54,28 +54,32 @@
 
 (defvar math-largest-emacs-expt
   (let ((x 1))
-    (while (condition-case nil
-               (expt 10.0 x)
-             (error nil))
+    (while (and (condition-case nil
+                   (expt 10.0 x)
+                 (error nil))
+               (< (expt 10.0 x) (expt 10.0 (* 2 x))))
       (setq x (* 2 x)))
     (setq x (/ x 2))
-    (while (condition-case nil
-               (expt 10.0 x)
-             (error nil))
+    (while (and (condition-case nil
+                   (expt 10.0 x)
+                 (error nil))
+               (< (expt 10.0 x) (expt 10.0 (* 2 x))))
       (setq x (1+ x)))
     (- x 2))
   "The largest exponent which Calc will convert to an Emacs float.")
 
 (defvar math-smallest-emacs-expt
   (let ((x -1))
-    (while (condition-case nil
-               (expt 10.0 x)
-             (error nil))
+    (while (and (condition-case nil
+                   (expt 10.0 x)
+                 (error nil))
+               (> (expt 10.0 x) 0.0))
       (setq x (* 2 x)))
     (setq x (/ x 2))
-    (while (condition-case nil
-               (expt 10.0 x)
-             (error nil))
+    (while (and (condition-case nil
+                   (expt 10.0 x)
+                 (error nil))
+               (> (expt 10.0 x) 0.0))
       (setq x (1- x)))
     (+ x 2))
     "The smallest exponent which Calc will convert to an Emacs float.")