From 873639d6fd11c734cee6ae566e6e1e377f208fe7 Mon Sep 17 00:00:00 2001
From: Thom Chiovoloni <chiovolonit@gmail.com>
Date: Wed, 7 Oct 2020 11:51:54 -0700
Subject: [PATCH 1/2] Use bitxor to implement Neg for floats

---
 crates/core_simd/src/ops.rs                     | 15 +++++++++++++--
 crates/core_simd/tests/ops_impl/float_macros.rs |  9 +++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/crates/core_simd/src/ops.rs b/crates/core_simd/src/ops.rs
index 5af10a4e1886..9e0bc3f42a66 100644
--- a/crates/core_simd/src/ops.rs
+++ b/crates/core_simd/src/ops.rs
@@ -212,7 +212,18 @@ macro_rules! impl_op {
             impl core::ops::Neg for $type {
                 type Output = Self;
                 fn neg(self) -> Self::Output {
-                    <$type>::splat(-<$scalar>::default()) - self
+                    <$type>::splat(0) - self
+                }
+            }
+        }
+    };
+
+    { impl Neg for $type:ty, $scalar:ty, @float } => {
+        impl_ref_ops! {
+            impl core::ops::Neg for $type {
+                type Output = Self;
+                fn neg(self) -> Self::Output {
+                    Self::from_bits(<$type>::splat(-0.0).to_bits() ^ self.to_bits())
                 }
             }
         }
@@ -310,7 +321,7 @@ macro_rules! impl_float_ops {
                 impl_op! { impl Mul for $vector, $scalar }
                 impl_op! { impl Div for $vector, $scalar }
                 impl_op! { impl Rem for $vector, $scalar }
-                impl_op! { impl Neg for $vector, $scalar }
+                impl_op! { impl Neg for $vector, $scalar, @float }
                 impl_op! { impl Index for $vector, $scalar }
             )*
         )*
diff --git a/crates/core_simd/tests/ops_impl/float_macros.rs b/crates/core_simd/tests/ops_impl/float_macros.rs
index 1c969a2e8af3..7df30ec39f6c 100644
--- a/crates/core_simd/tests/ops_impl/float_macros.rs
+++ b/crates/core_simd/tests/ops_impl/float_macros.rs
@@ -289,6 +289,15 @@ macro_rules! float_tests {
                 assert_biteq!(-v, expected);
             }
 
+            #[test]
+            #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+            fn neg_odd_floats() {
+                for v in slice_chunks(&C) {
+                    let expected = apply_unary_lanewise(v, core::ops::Neg::neg);
+                    assert_biteq!(-v, expected);
+                }
+            }
+
             #[test]
             #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
             fn abs_negative() {

From ffd562f2181f5969d56c4a6c9399be27058c8a74 Mon Sep 17 00:00:00 2001
From: Thom Chiovoloni <chiovolonit@gmail.com>
Date: Wed, 7 Oct 2020 13:24:21 -0700
Subject: [PATCH 2/2] Add comment about fneg to the bitxor in float neg

---
 crates/core_simd/src/ops.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/crates/core_simd/src/ops.rs b/crates/core_simd/src/ops.rs
index 9e0bc3f42a66..5a186649821b 100644
--- a/crates/core_simd/src/ops.rs
+++ b/crates/core_simd/src/ops.rs
@@ -223,6 +223,8 @@ macro_rules! impl_op {
             impl core::ops::Neg for $type {
                 type Output = Self;
                 fn neg(self) -> Self::Output {
+                    // FIXME: Replace this with fneg intrinsic once available.
+                    // https://github.com/rust-lang/stdsimd/issues/32
                     Self::from_bits(<$type>::splat(-0.0).to_bits() ^ self.to_bits())
                 }
             }