From cdddbc6dcdabef73aeb20bb9b81e08dba92a235c Mon Sep 17 00:00:00 2001
From: Richard Kreckel <kreckel@ginac.de>
Date: Mon, 3 Aug 2020 18:09:30 +0200
Subject: [PATCH] [BUGFIX] Fix factor_univariate(poly, x) for constant poly.

The modular factorization fails to find a prime in this case, leading to
an infinite loop. At least one caller (factor_sqrfree) happens to produce
such constant polys in some cases.
---
 check/exam_factor.cpp | 7 ++-----
 ginac/factor.cpp      | 7 +++++--
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/check/exam_factor.cpp b/check/exam_factor.cpp
index c1e98e70..c848fdd4 100644
--- a/check/exam_factor.cpp
+++ b/check/exam_factor.cpp
@@ -26,8 +26,6 @@ using namespace GiNaC;
 #include <iostream>
 using namespace std;
 
-static symbol w("w"), x("x"), y("y"), z("z");
-
 static unsigned check_factor(const ex& e)
 {
 	ex ee = e.expand();
@@ -44,8 +42,7 @@ static unsigned exam_factor1()
 	unsigned result = 0;
 	ex e;
 	symbol x("x");
-	lst syms;
-	syms.append(x);
+	lst syms = {x};
 	
 	e = ex("1+x-x^3", syms);
 	result += check_factor(e);
@@ -199,7 +196,7 @@ static unsigned exam_factor_wang()
 	// "An Improved Multivariate Polynomial Factoring Algorithm"
 	unsigned result = 0;
 	ex e;
-	symbol x("x"), y("y"), z("z"), u("u");
+	symbol u("u"), w("w"), x("x"), y("y"), z("z");
 
 	e = ex("(z+x*y+10)*(x*z+y+30)*(y*z+x+20)", lst{x, y, z});
 	result += check_factor_expanded(e);
diff --git a/ginac/factor.cpp b/ginac/factor.cpp
index bb20589b..f53642a2 100644
--- a/ginac/factor.cpp
+++ b/ginac/factor.cpp
@@ -1491,6 +1491,9 @@ static ex factor_univariate(const ex& poly, const ex& x, unsigned int& prime)
 	poly.unitcontprim(x, unit, cont, prim_ex);
 	upoly prim;
 	upoly_from_ex(prim, prim_ex, x);
+	if (prim_ex.is_equal(1)) {
+		return poly;
+	}
 
 	// determine proper prime and minimize number of modular factors
 	prime = 3;
@@ -2454,9 +2457,9 @@ static ex factor_sqrfree(const ex& poly)
 	if ( findsymbols.syms.size() == 1 ) {
 		// univariate case
 		const ex& x = *(findsymbols.syms.begin());
-		if ( poly.ldegree(x) > 0 ) {
+		int ld = poly.ldegree(x);
+		if ( ld > 0 ) {
 			// pull out direct factors
-			int ld = poly.ldegree(x);
 			ex res = factor_univariate(expand(poly/pow(x, ld)), x);
 			return res * pow(x,ld);
 		} else {
-- 
2.44.0