From a3e672f863b7bc9dc3191f3b728eb360d8509482 Mon Sep 17 00:00:00 2001
From: Prateek Machiraju <prateek.machiraju@gmail.com>
Date: Thu, 8 Oct 2020 00:59:34 -0400
Subject: [PATCH] [wpimath] C++: Assign zero in MakeWhiteNoiseVector if std-dev
 is zero (#2773)

A std-dev of zero is UB in C++. Java does not have this issue.

Co-authored-by: Tyler Veness <calcmogul@gmail.com>
---
 wpimath/src/main/native/include/frc/StateSpaceUtil.h | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/wpimath/src/main/native/include/frc/StateSpaceUtil.h b/wpimath/src/main/native/include/frc/StateSpaceUtil.h
index e19dd1a443..b461005085 100644
--- a/wpimath/src/main/native/include/frc/StateSpaceUtil.h
+++ b/wpimath/src/main/native/include/frc/StateSpaceUtil.h
@@ -220,8 +220,14 @@ Eigen::Matrix<double, N, 1> MakeWhiteNoiseVector(
 
   Eigen::Matrix<double, N, 1> result;
   for (int i = 0; i < N; ++i) {
-    std::normal_distribution<> distr{0.0, stdDevs[i]};
-    result(i) = distr(gen);
+    // Passing a standard deviation of 0.0 to std::normal_distribution is
+    // undefined behavior
+    if (stdDevs[i] == 0.0) {
+      result(i) = 0.0;
+    } else {
+      std::normal_distribution distr{0.0, stdDevs[i]};
+      result(i) = distr(gen);
+    }
   }
   return result;
 }