From 2eac902c33832c8888ffd52f36d3fccf04cc6c49 Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Tue, 19 May 2020 10:45:54 -0600
Subject: [PATCH] correct fixnum overflow on negation (#528)

---
 src/prolog/arithmetic.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/prolog/arithmetic.rs b/src/prolog/arithmetic.rs
index 87df3dbd..e889b019 100644
--- a/src/prolog/arithmetic.rs
+++ b/src/prolog/arithmetic.rs
@@ -474,7 +474,12 @@ impl Neg for Number {
 
     fn neg(self) -> Self::Output {
         match self {
-            Number::Fixnum(n) => Number::Fixnum(-n),
+            Number::Fixnum(n) =>
+                if let Some(n) = n.checked_neg() {
+                    Number::Fixnum(n)
+                } else {
+                    Number::from(-Integer::from(n))
+                }
             Number::Integer(n) => Number::Integer(Rc::new(-Integer::from(&*n))),
             Number::Float(OrderedFloat(f)) => Number::Float(OrderedFloat(-f)),
             Number::Rational(r) => Number::Rational(Rc::new(-Rational::from(&*r))),
-- 
2.54.0