Calc: GCD(0,x)=GCD(x,0)=|x|, not x (bug#41279)

Reported by David Ongaro.

* lisp/calc/calc-comb.el (calcFunc-gcd): Fix GCD simplification.
* test/lisp/calc/calc-tests.el (calc-gcd, calc-sum-gcd): New tests.

1 files changed, 2 insertions, 2 deletions

diff --git a/lisp/calc/calc-comb.el b/lisp/calc/calc-comb.el
index d4562a0cc86..c5d4d0837e7 100644
--- a/lisp/calc/calc-comb.el
+++ b/lisp/calc/calc-comb.el
@@ -241,8 +241,8 @@
          (calcFunc-gcd (math-neg a) b))
         ((Math-looks-negp b)
          (calcFunc-gcd a (math-neg b)))
-        ((Math-zerop a) b)
-        ((Math-zerop b) a)
+        ((Math-zerop a) (math-abs b))
+        ((Math-zerop b) (math-abs a))
         ((and (Math-ratp a)
               (Math-ratp b))
          (math-make-frac (math-gcd (if (eq (car-safe a) 'frac) (nth 1 a) a)