Fix Signum for no_std

Author: Ogeon

palette/src/num.rs

@@ -716,6 +716,7 @@ macro_rules! impl_float {
                 }
             }
 
+            #[cfg(feature = "std")]
             impl Signum for $ty {
                 #[inline]
                 fn signum(self) -> Self {

palette/src/num/libm.rs

@@ -253,3 +253,25 @@ impl MulAdd for f64 {
         ::libm::fma(self, m, a)
     }
 }
+
+impl Signum for f32 {
+    #[inline]
+    fn signum(self) -> Self {
+        if self.is_nan() {
+            Self::NAN
+        } else {
+            ::libm::copysignf(1.0, self)
+        }
+    }
+}
+
+impl Signum for f64 {
+    #[inline]
+    fn signum(self) -> Self {
+        if self.is_nan() {
+            Self::NAN
+        } else {
+            ::libm::copysign(1.0, self)
+        }
+    }
+}

palette/src/num/wide.rs

@@ -302,7 +302,7 @@ macro_rules! impl_wide_float {
             impl Signum for $ty {
                 #[inline]
                 fn signum(self) -> Self {
-                    $ty::copysign(self, Self::from(1.0))
+                    self.is_nan().blend(Self::from($scalar::NAN), $ty::copysign(Self::from(1.0), self))
                 }
             }
         )+