From 581a8e26f1c014a097ab4934cdc283fb7dfc7ea1 Mon Sep 17 00:00:00 2001
From: Jeff Wang <jeff.wang@utexas.edu>
Date: Mon, 21 Oct 2019 02:31:18 -0400
Subject: [PATCH] disallow subtraction/negation of error

---
 src/decn/decn.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/decn/decn.c b/src/decn/decn.c
index 9917d5a..f994dea 100644
--- a/src/decn/decn.c
+++ b/src/decn/decn.c
@@ -406,6 +406,9 @@ void negate_decn(dec80* x){
 #else
 	static const exp_t xor_val = -(0x7f) - 1;
 #endif
+	if (decn_is_nan(x)){
+		return;
+	}
 	(x->exponent) ^= xor_val;
 }