Treat wasmtime::component::Val::Float{32,64} zero and negative zero…

… as inequal (#5562)

Following up on #5535, treat positive and negative zero as inequal in
wasmtime::component::Val::Float{32,64}'s `PartialEq` logic. IEEE 754
equality considers these values equal, but they are semantically
distinct values, and testing and fuzzing should be aware of the
difference.

crates/wasmtime/src/component/values.rs

@@ -1007,10 +1007,22 @@ impl Val {
 impl PartialEq for Val {
     fn eq(&self, other: &Self) -> bool {
         match (self, other) {
-            // This breaks conformance with IEEE-754 equality to simplify testing logic.
-            (Self::Float32(l), Self::Float32(r)) => l == r || (l.is_nan() && r.is_nan()),
+            // IEEE 754 equality considers NaN inequal to NaN and negative zero
+            // equal to positive zero, however we do the opposite here, because
+            // this logic is used by testing and fuzzing, which want to know
+            // whether two values are semantically the same, rather than
+            // numerically equal.
+            (Self::Float32(l), Self::Float32(r)) => {
+                (*l != 0.0 && l == r)
+                    || (*l == 0.0 && l.to_bits() == r.to_bits())
+                    || (l.is_nan() && r.is_nan())
+            }
             (Self::Float32(_), _) => false,
-            (Self::Float64(l), Self::Float64(r)) => l == r || (l.is_nan() && r.is_nan()),
+            (Self::Float64(l), Self::Float64(r)) => {
+                (*l != 0.0 && l == r)
+                    || (*l == 0.0 && l.to_bits() == r.to_bits())
+                    || (l.is_nan() && r.is_nan())
+            }
             (Self::Float64(_), _) => false,
 
             (Self::Bool(l), Self::Bool(r)) => l == r,