Fix for calculating large factorials

Fix for calculating large factorials

[michael schuldt]

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I was playing around with calc bignums and found that calculating the
factorial of
large numbers results in the error "Variable binding depth exceeds
max-specpdl-size".

I though this might be a good chance to try out the contribution process,
I've attached
a path which simply eliminates the troublesome recursiveness of
math-factorial-iter.


-Michael

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From 9cfd3c86f2490e2033fee1c3647f4b01029ff047 Mon Sep 17 00:00:00 2001
From: mschuldt <mbschuldt@gmail.com>
Date: Tue, 18 Apr 2017 01:25:28 -0700
Subject: [PATCH] Non-recursive version of math-factorial-iter. Prevents error
 "Variable binding depth exceeds max-specpdl-size"

---
 lisp/calc/calc-comb.el | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/lisp/calc/calc-comb.el b/lisp/calc/calc-comb.el
index c84ff23..a033d27 100644
--- a/lisp/calc/calc-comb.el
+++ b/lisp/calc/calc-comb.el
@@ -362,11 +362,13 @@
     (math-gammap1-raw '(float -25 -2))))
 
 (defun math-factorial-iter (count n f)
-  (if (= (% n 5) 1)
-      (math-working (format "factorial(%d)" (1- n)) f))
-  (if (> count 0)
-      (math-factorial-iter (1- count) (1+ n) (math-mul n f))
-    f))
+  (while (> count 0)
+    (if (= (% n 5) 1)
+        (math-working (format "factorial(%d)" (1- n)) f))
+    (setq count (1- count)
+          f (math-mul n f)
+          n (1+ n)))
+  f)
 
 (defun calcFunc-dfact (n)   ; [I I] [F F] [Public]
   (cond ((Math-integer-negp n)
-- 
2.7.4

Re: Fix for calculating large factorials

[Paul Eggert]

Thanks for the fix. I installed it here:

http://git.savannah.gnu.org/cgit/emacs.git/commit/?id=d831312d668fbedeffe3711b13cd455309da84a1