From 68f9c65bb1191b789918292a2ad25c0f8b227421 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timoth=C3=A9e=20Haudebourg?=
 <timothee.haudebourg@hemisemi.fr>
Date: Fri, 5 Nov 2021 12:51:02 +0100
Subject: [PATCH] Use the same hash for +0 and -0.

---
 src/number.rs |  9 ++++++++-
 tests/test.rs | 17 +++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/number.rs b/src/number.rs
index ad59ae6dd..a5771dbbd 100644
--- a/src/number.rs
+++ b/src/number.rs
@@ -55,7 +55,14 @@ impl core::hash::Hash for N {
             N::NegInt(i) => i.hash(h),
             N::Float(f) => {
                 // Using `f64::to_bits` here is fine since any float values are never `NaN`.
-                f.to_bits().hash(h);
+                if *f == 0.0f64 {
+                    // The IEEE 754 standard has two representations for zero, +0 and -0,
+                    // such that +0 == -0.
+                    // In this case we use the +0 hash so that hash(+0) == hash(-0).
+                    0.0f64.to_bits().hash(h);
+                } else {
+                    f.to_bits().hash(h);
+                }
             }
         }
     }
diff --git a/tests/test.rs b/tests/test.rs
index c8df23dba..25198f5d3 100644
--- a/tests/test.rs
+++ b/tests/test.rs
@@ -2284,3 +2284,20 @@ fn test_value_into_deserializer() {
     let outer = Outer::deserialize(map.into_deserializer()).unwrap();
     assert_eq!(outer.inner.string, "Hello World");
 }
+
+#[test]
+fn hash_positive_and_negative_zero() {
+    use std::collections::hash_map::DefaultHasher;
+    use std::hash::{Hash, Hasher};
+
+    fn hash(obj: impl Hash) -> u64 {
+        let mut hasher = DefaultHasher::new();
+        obj.hash(&mut hasher);
+        hasher.finish()
+    }
+
+    let k1 = serde_json::from_str::<Number>("0.0").unwrap();
+    let k2 = serde_json::from_str::<Number>("-0.0").unwrap();
+    assert_eq!(k1, k2);
+    assert_eq!(hash(k1), hash(k2));
+}