cleanup FlushSubnormals implementation

Author: folkertdev

crates/test_helpers/src/subnormals.rs

@@ -7,81 +7,45 @@ pub trait FlushSubnormals: Sized {
 impl<T> FlushSubnormals for *const T {}
 impl<T> FlushSubnormals for *mut T {}
 
-macro_rules! impl_float {
-    { $($ty:ty),* } => {
-        $(
-        impl FlushSubnormals for $ty {
-            fn flush(self) -> Self {
-                let is_f32 = size_of::<Self>() == 4;
-                let ppc_flush = is_f32 && cfg!(all(
-                    any(target_arch = "powerpc", all(target_arch = "powerpc64", target_endian = "big")),
-                    target_feature = "altivec",
-                    not(target_feature = "vsx"),
-                ));
-                let arm_flush = is_f32 && cfg!(all(target_arch = "arm", target_feature = "neon"));
-                let flush = ppc_flush || arm_flush;
-                if flush && self.is_subnormal() {
-                    <$ty>::copysign(0., self)
-                } else {
-                    self
-                }
-            }
+impl FlushSubnormals for i8 {}
+impl FlushSubnormals for i16 {}
+impl FlushSubnormals for i32 {}
+impl FlushSubnormals for i64 {}
+impl FlushSubnormals for isize {}
+
+impl FlushSubnormals for u8 {}
+impl FlushSubnormals for u16 {}
+impl FlushSubnormals for u32 {}
+impl FlushSubnormals for u64 {}
+impl FlushSubnormals for usize {}
+
+impl FlushSubnormals for f16 {}
+impl FlushSubnormals for f64 {}
+
+impl FlushSubnormals for f32 {
+    fn flush(self) -> Self {
+        // Correct for non-IEEE behavior for f32 on arm and powerpc.
+        let ppc_flush = cfg!(all(
+            any(
+                target_arch = "powerpc",
+                all(target_arch = "powerpc64", target_endian = "big")
+            ),
+            target_feature = "altivec",
+            not(target_feature = "vsx"),
+        ));
+        let arm_flush = cfg!(all(target_arch = "arm", target_feature = "neon"));
+        let flush = ppc_flush || arm_flush;
+
+        if flush && self.is_subnormal() {
+            f32::copysign(0.0, self)
+        } else {
+            self
         }
-        )*
-    }
-}
-
-macro_rules! impl_else {
-    { $($ty:ty),* } => {
-        $(
-        impl FlushSubnormals for $ty {}
-        )*
     }
 }
 
-impl_float! { f16, f32, f64 }
-impl_else! { i8, i16, i32, i64, isize, u8, u16, u32, u64, usize }
-
-/// AltiVec should flush subnormal inputs to zero, but QEMU seems to only flush outputs.
+/// NOTE: altivec had a subnormal flushing bug in older QEMU versions.
 /// https://gitlab.com/qemu-project/qemu/-/issues/1779
-#[cfg(all(
-    any(target_arch = "powerpc", target_arch = "powerpc64"),
-    target_feature = "altivec"
-))]
-fn in_buggy_qemu() -> bool {
-    use std::sync::OnceLock;
-    static BUGGY: OnceLock<bool> = OnceLock::new();
-
-    fn add(x: f32, y: f32) -> f32 {
-        #[cfg(target_arch = "powerpc")]
-        use core::arch::powerpc::*;
-        #[cfg(target_arch = "powerpc64")]
-        use core::arch::powerpc64::*;
-
-        let array: [f32; 4] =
-            unsafe { core::mem::transmute(vec_add(vec_splats(x), vec_splats(y))) };
-        array[0]
-    }
-
-    *BUGGY.get_or_init(|| add(-1.0857398e-38, 0.).is_sign_negative())
-}
-
-#[cfg(all(
-    any(target_arch = "powerpc", target_arch = "powerpc64"),
-    target_feature = "altivec"
-))]
-pub fn flush_in<T: FlushSubnormals>(x: T) -> T {
-    if in_buggy_qemu() {
-        x
-    } else {
-        x.flush()
-    }
-}
-
-#[cfg(not(all(
-    any(target_arch = "powerpc", target_arch = "powerpc64"),
-    target_feature = "altivec"
-)))]
 pub fn flush_in<T: FlushSubnormals>(x: T) -> T {
     x.flush()
 }