Add primitive documentation for f16 and f128

Author: tgross35

library/core/src/primitive_docs.rs

@@ -1074,7 +1074,22 @@ mod prim_tuple {}
 #[doc(hidden)]
 impl<T> (T,) {}
 
+#[rustc_doc_primitive = "f16"]
+#[doc(alias = "half")]
+/// A 16-bit floating point type (specifically, the "binary16" type defined in IEEE 754-2008).
+///
+/// This type is very similar to [`prim@f32`] but has decreased precision because it uses half as many
+/// bits. Please see [the documentation for [`prim@f32`] or [Wikipedia on
+/// half-precision values][wikipedia] for more information.
+///
+/// *[See also the `std::f16::consts` module](crate::f16::consts).*
+///
+/// [wikipedia]: https://en.wikipedia.org/wiki/Half-precision_floating-point_format
+#[unstable(feature = "f16", issue = "116909")]
+mod prim_f16 {}
+
 #[rustc_doc_primitive = "f32"]
+#[doc(alias = "single")]
 /// A 32-bit floating point type (specifically, the "binary32" type defined in IEEE 754-2008).
 ///
 /// This type can represent a wide range of decimal numbers, like `3.5`, `27`,
@@ -1143,6 +1158,7 @@ impl<T> (T,) {}
 mod prim_f32 {}
 
 #[rustc_doc_primitive = "f64"]
+#[doc(alias = "double")]
 /// A 64-bit floating point type (specifically, the "binary64" type defined in IEEE 754-2008).
 ///
 /// This type is very similar to [`f32`], but has increased
@@ -1157,6 +1173,20 @@ mod prim_f32 {}
 #[stable(feature = "rust1", since = "1.0.0")]
 mod prim_f64 {}
 
+#[rustc_doc_primitive = "f128"]
+#[doc(alias = "quad")]
+/// A 128-bit floating point type (specifically, the "binary128" type defined in IEEE 754-2008).
+///
+/// This type is very similar to [`prim@f32`] and [`prim@f64`], but has increased precision by using twice
+/// as many bits as `f64`. Please see [the documentation for [`prim@f32`] or [Wikipedia on
+/// quad-precision values][wikipedia] for more information.
+///
+/// *[See also the `std::f128::consts` module](crate::f128::consts).*
+///
+/// [wikipedia]: https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format
+#[unstable(feature = "f128", issue = "116909")]
+mod prim_f128 {}
+
 #[rustc_doc_primitive = "i8"]
 //
 /// The 8-bit signed integer type.