Re: calc: E command hangs Emacs.

[Michaël Cadilhac]

"yu jie" <address@hidden> writes:

>> (let ((x -1))
>>   (while (condition-case nil
>>           (message "1.Expt is %e" (expt 10.0 x))
>>         (error nil))
>>     (message "1.`x' is now %d" (setq x (* 2 x))))
>>   (message "2.`x' is now %d" (setq x (/ x 2)))
>>   (while (condition-case nil
>>           (message "3.Expt is %e" (expt 10.0 x))
>>         (error nil))
>>     (message "3.`x' is now %d" (setq x (1- x))))
>>   (+ x 2))

> *Message*:
> 1.Expt is 1.000000e+000
> 1.`x' is now 0
> 1.Expt is 1.000000e+000
> 1.`x' is now 0
> 1.Expt is 1.000000e+000
> 1.`x' is now 0
> 1.Expt is 1.000000e+000
> Loading debug...done
> Entering debugger...

Thanks a lot.  As I read the pow(3) man page, the fact that it triggers
a ERANGE error is not documented, so it doesn't seem standard.

IMO, we should check by hand if an (under|over)flow is triggered.

Can you please try the following patch?

--- floatfns.c  26 Jul 2007 07:27:51 +0200      1.94
+++ floatfns.c  21 Sep 2007 11:22:16 +0200      
@@ -454,7 +454,7 @@
      (arg1, arg2)
      register Lisp_Object arg1, arg2;
 {
-  double f1, f2;
+  double f1, f2, f3;
 
   CHECK_NUMBER_OR_FLOAT (arg1);
   CHECK_NUMBER_OR_FLOAT (arg2);
@@ -500,8 +500,11 @@
   else if ((f1 == 0.0 && f2 < 0.0) || (f1 < 0 && f2 != floor(f2)))
     domain_error2 ("expt", arg1, arg2);
 #endif
-  IN_FLOAT2 (f1 = pow (f1, f2), "expt", arg1, arg2);
-  return make_float (f1);
+  IN_FLOAT2 (f3 = pow (f1, f2), "expt", arg1, arg2);
+  /* Check for overflow in the result.  */
+  if (f1 != 0.0 && f3 == 0.0)
+    range_error ("expt", arg1);
+  return make_float (f3);
 }
 
 DEFUN ("log", Flog, Slog, 1, 2, 0,

Thanks again.

-- 
 |   Michaël `Micha' Cadilhac       |  Would someone please DTRT with this,  |
 |   http://michael.cadilhac.name   |        then ACK?                       |
 |   JID/MSN:                       |          -- Richard Stallman           |
 `----  address@hidden  |                                   -  --'

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