Fix stack overflow

Fixes #242

src/traits.rs

@@ -183,12 +183,12 @@ pub trait Sign {
 
   /// Returns whether the value is positive.
   fn is_sign_positive(&self) -> bool {
-    self.sign().is_sign_positive()
+    f32::is_sign_positive(self.sign())
   }
 
   /// Returns whether the value is negative.
   fn is_sign_negative(&self) -> bool {
-    self.sign().is_sign_negative()
+    f32::is_sign_negative(self.sign())
   }
 }
 
@@ -199,12 +199,12 @@ pub trait TrySign {
 
   /// Returns whether the value is positive. If not possible, returns false.
   fn is_sign_positive(&self) -> bool {
-    self.try_sign().map_or(false, |s| s.is_sign_positive())
+    self.try_sign().map_or(false, |s| f32::is_sign_positive(s))
   }
 
   /// Returns whether the value is negative. If not possible, returns false.
   fn is_sign_negative(&self) -> bool {
-    self.try_sign().map_or(false, |s| s.is_sign_negative())
+    self.try_sign().map_or(false, |s| f32::is_sign_negative(s))
   }
 }
 

src/values/number.rs

@@ -91,7 +91,7 @@ impl Map for CSSNumber {
 impl Sign for CSSNumber {
   fn sign(&self) -> f32 {
     if *self == 0.0 {
-      return if self.is_sign_positive() { 0.0 } else { -0.0 };
+      return if f32::is_sign_positive(*self) { 0.0 } else { -0.0 };
     }
     self.signum()
   }