Add {leading,trailing}_ones to primitive int types

Author: Thom Chiovoloni

src/libcore/num/mod.rs

@@ -393,6 +393,48 @@ $EndFeature, "
             }
         }
 
+        doc_comment! {
+            concat!("Returns the number of leading ones in the binary representation of `self`.
+
+# Examples
+
+Basic usage:
+
+```
+", $Feature, "#![feature(leading_trailing_ones)]
+let n = -1", stringify!($SelfT), ";
+
+assert_eq!(n.leading_ones(), ", stringify!($BITS), ");",
+$EndFeature, "
+```"),
+            #[unstable(feature = "leading_trailing_ones", reason = "newly added", issue = "0")]
+            #[inline]
+            pub const fn leading_ones(self) -> u32 {
+                (self as $UnsignedT).leading_ones()
+            }
+        }
+
+        doc_comment! {
+            concat!("Returns the number of trailing ones in the binary representation of `self`.
+
+# Examples
+
+Basic usage:
+
+```
+", $Feature, "#![feature(leading_trailing_ones)]
+let n = 3", stringify!($SelfT), ";
+
+assert_eq!(n.trailing_ones(), 2);",
+$EndFeature, "
+```"),
+            #[unstable(feature = "leading_trailing_ones", reason = "newly added", issue = "0")]
+            #[inline]
+            pub const fn trailing_ones(self) -> u32 {
+                (self as $UnsignedT).trailing_ones()
+            }
+        }
+
         doc_comment! {
             concat!("Shifts the bits to the left by a specified amount, `n`,
 wrapping the truncated bits to the end of the resulting integer.
@@ -2485,6 +2527,47 @@ assert_eq!(n.trailing_zeros(), 3);", $EndFeature, "
             }
         }
 
+        doc_comment! {
+            concat!("Returns the number of leading ones in the binary representation of `self`.
+
+# Examples
+
+Basic usage:
+
+```
+", $Feature, "#![feature(leading_trailing_ones)]
+let n = !(", stringify!($SelfT), "::max_value() >> 2);
+
+assert_eq!(n.leading_ones(), 2);", $EndFeature, "
+```"),
+            #[unstable(feature = "leading_trailing_ones", reason = "newly added", issue = "0")]
+            #[inline]
+            pub const fn leading_ones(self) -> u32 {
+                (!self).leading_zeros()
+            }
+        }
+
+        doc_comment! {
+            concat!("Returns the number of trailing ones in the binary representation
+of `self`.
+
+# Examples
+
+Basic usage:
+
+```
+", $Feature, "#![feature(leading_trailing_ones)]
+let n = 0b1010111", stringify!($SelfT), ";
+
+assert_eq!(n.trailing_ones(), 3);", $EndFeature, "
+```"),
+            #[unstable(feature = "leading_trailing_ones", reason = "newly added", issue = "0")]
+            #[inline]
+            pub const fn trailing_ones(self) -> u32 {
+                (!self).trailing_zeros()
+            }
+        }
+
         doc_comment! {
             concat!("Shifts the bits to the left by a specified amount, `n`,
 wrapping the truncated bits to the end of the resulting integer.