Rollup merge of rust-lang#76941 - clarfonthey:is_subnormal, r=m-ou-se

Add f{32,64}::is_subnormal

The docs recommend that you use dedicated methods instead of calling `classify` directly, although there isn't actually a way of checking if a number is subnormal without calling classify. There are dedicated methods for all other forms, excluding `is_zero` (which is just `== 0.0` anyway).

Author: m-ou-se

library/core/src/num/f32.rs

@@ -441,6 +441,32 @@ impl f32 {
         self.abs_private() < Self::INFINITY
     }
 
+    /// Returns `true` if the number is [subnormal].
+    ///
+    /// ```
+    /// #![feature(is_subnormal)]
+    /// let min = f32::MIN_POSITIVE; // 1.17549435e-38f32
+    /// let max = f32::MAX;
+    /// let lower_than_min = 1.0e-40_f32;
+    /// let zero = 0.0_f32;
+    ///
+    /// assert!(!min.is_subnormal());
+    /// assert!(!max.is_subnormal());
+    ///
+    /// assert!(!zero.is_subnormal());
+    /// assert!(!f32::NAN.is_subnormal());
+    /// assert!(!f32::INFINITY.is_subnormal());
+    /// // Values between `0` and `min` are Subnormal.
+    /// assert!(lower_than_min.is_subnormal());
+    /// ```
+    /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
+    #[unstable(feature = "is_subnormal", issue = "79288")]
+    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[inline]
+    pub const fn is_subnormal(self) -> bool {
+        matches!(self.classify(), FpCategory::Subnormal)
+    }
+
     /// Returns `true` if the number is neither zero, infinite,
     /// [subnormal], or `NaN`.
     ///

library/core/src/num/f64.rs

@@ -440,6 +440,32 @@ impl f64 {
         self.abs_private() < Self::INFINITY
     }
 
+    /// Returns `true` if the number is [subnormal].
+    ///
+    /// ```
+    /// #![feature(is_subnormal)]
+    /// let min = f64::MIN_POSITIVE; // 2.2250738585072014e-308_f64
+    /// let max = f64::MAX;
+    /// let lower_than_min = 1.0e-308_f64;
+    /// let zero = 0.0_f64;
+    ///
+    /// assert!(!min.is_subnormal());
+    /// assert!(!max.is_subnormal());
+    ///
+    /// assert!(!zero.is_subnormal());
+    /// assert!(!f64::NAN.is_subnormal());
+    /// assert!(!f64::INFINITY.is_subnormal());
+    /// // Values between `0` and `min` are Subnormal.
+    /// assert!(lower_than_min.is_subnormal());
+    /// ```
+    /// [subnormal]: https://en.wikipedia.org/wiki/Denormal_number
+    #[unstable(feature = "is_subnormal", issue = "79288")]
+    #[rustc_const_unstable(feature = "const_float_classify", issue = "72505")]
+    #[inline]
+    pub const fn is_subnormal(self) -> bool {
+        matches!(self.classify(), FpCategory::Subnormal)
+    }
+
     /// Returns `true` if the number is neither zero, infinite,
     /// [subnormal], or `NaN`.
     ///