From 4679f0567305341aee9d4563e7626d19859d77ee Mon Sep 17 00:00:00 2001
From: "Fabio A. Correa" <facorread@gmail.com>
Date: Thu, 26 Mar 2020 16:50:29 -0400
Subject: [PATCH] Rounding error fix on WeightedIndex::update_weights()

WeightedIndex::update_weights() uses subtraction on old_w. Rounding errors, particularly on f32, may bring total_weight to below 0. This PR makes sure a negative total_weight results in an error.

This replaces PR #955 which was invalidated after a merge. Thanks for your consideration!
---
 src/distributions/weighted_index.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/distributions/weighted_index.rs b/src/distributions/weighted_index.rs
index 5a3ecaa2099..b73bc43af02 100644
--- a/src/distributions/weighted_index.rs
+++ b/src/distributions/weighted_index.rs
@@ -174,7 +174,7 @@ impl<X: SampleUniform + PartialOrd> WeightedIndex<X> {
             total_weight += w;
             prev_i = Some(i);
         }
-        if total_weight == zero {
+        if total_weight <= zero {
             return Err(WeightedError::AllWeightsZero);
         }