5 files changed, 102 insertions, 7 deletions
diff --git a/src/libcore/hash/mod.rs b/src/libcore/hash/mod.rs
index d80101753cb..6abe19dc155 100644
--- a/src/libcore/hash/mod.rs
+++ b/src/libcore/hash/mod.rs
@@ -333,31 +333,31 @@ pub trait Hasher {
     #[inline]
     #[stable(feature = "hasher_write", since = "1.3.0")]
     fn write_i16(&mut self, i: i16) {
-        self.write(&i.to_ne_bytes())
+        self.write_u16(i as u16)
     }
     /// Writes a single `i32` into this hasher.
     #[inline]
     #[stable(feature = "hasher_write", since = "1.3.0")]
     fn write_i32(&mut self, i: i32) {
-        self.write(&i.to_ne_bytes())
+        self.write_u32(i as u32)
     }
     /// Writes a single `i64` into this hasher.
     #[inline]
     #[stable(feature = "hasher_write", since = "1.3.0")]
     fn write_i64(&mut self, i: i64) {
-        self.write(&i.to_ne_bytes())
+        self.write_u64(i as u64)
     }
     /// Writes a single `i128` into this hasher.
     #[inline]
     #[stable(feature = "i128", since = "1.26.0")]
     fn write_i128(&mut self, i: i128) {
-        self.write(&i.to_ne_bytes())
+        self.write_u128(i as u128)
     }
     /// Writes a single `isize` into this hasher.
     #[inline]
     #[stable(feature = "hasher_write", since = "1.3.0")]
     fn write_isize(&mut self, i: isize) {
-        self.write(&i.to_ne_bytes())
+        self.write_usize(i as usize)
     }
 }
 
diff --git a/src/libcore/lib.rs b/src/libcore/lib.rs
index 2b26e5303a8..15466ce94a8 100644
--- a/src/libcore/lib.rs
+++ b/src/libcore/lib.rs
@@ -279,9 +279,9 @@ pub mod primitive;
 // crate uses the this crate as its libcore.
 #[path = "../stdarch/crates/core_arch/src/mod.rs"]
 #[allow(missing_docs, missing_debug_implementations, dead_code, unused_imports)]
-// FIXME: This annotation should be moved into rust-lang/stdarch after clashing_extern_decl is
+// FIXME: This annotation should be moved into rust-lang/stdarch after clashing_extern_declarations is
 // merged. It currently cannot because bootstrap fails as the lint hasn't been defined yet.
-#[cfg_attr(not(bootstrap), allow(clashing_extern_decl))]
+#[cfg_attr(not(bootstrap), allow(clashing_extern_declarations))]
 #[unstable(feature = "stdsimd", issue = "48556")]
 mod core_arch;
 
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index 57bacdd99ef..6a50cdbc1d9 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -2663,6 +2663,60 @@ impl<T> [T] {
     {
         self.iter().is_sorted_by_key(f)
     }
+
+    /// Returns the index of the partition point according to the given predicate
+    /// (the index of the first element of the second partition).
+    ///
+    /// The slice is assumed to be partitioned according to the given predicate.
+    /// This means that all elements for which the predicate returns true are at the start of the slice
+    /// and all elements for which the predicate returns false are at the end.
+    /// For example, [7, 15, 3, 5, 4, 12, 6] is a partitioned under the predicate x % 2 != 0
+    /// (all odd numbers are at the start, all even at the end).
+    ///
+    /// If this slice is not partitioned, the returned result is unspecified and meaningless,
+    /// as this method performs a kind of binary search.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(partition_point)]
+    ///
+    /// let v = [1, 2, 3, 3, 5, 6, 7];
+    /// let i = v.partition_point(|&x| x < 5);
+    ///
+    /// assert_eq!(i, 4);
+    /// assert!(v[..i].iter().all(|&x| x < 5));
+    /// assert!(v[i..].iter().all(|&x| !(x < 5)));
+    /// ```
+    #[unstable(feature = "partition_point", reason = "new API", issue = "73831")]
+    pub fn partition_point<P>(&self, mut pred: P) -> usize
+    where
+        P: FnMut(&T) -> bool,
+    {
+        let mut left = 0;
+        let mut right = self.len();
+
+        while left != right {
+            let mid = left + (right - left) / 2;
+            // SAFETY:
+            // When left < right, left <= mid < right.
+            // Therefore left always increases and right always decreases,
+            // and eigher of them is selected.
+            // In both cases left <= right is satisfied.
+            // Therefore if left < right in a step,
+            // left <= right is satisfied in the next step.
+            // Therefore as long as left != right, 0 <= left < right <= len is satisfied
+            // and if this case 0 <= mid < len is satisfied too.
+            let value = unsafe { self.get_unchecked(mid) };
+            if pred(value) {
+                left = mid + 1;
+            } else {
+                right = mid;
+            }
+        }
+
+        left
+    }
 }
 
 #[lang = "slice_u8"]
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 4e55452a4c3..524c38a7ab4 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -44,6 +44,7 @@
 #![feature(const_forget)]
 #![feature(option_unwrap_none)]
 #![feature(peekable_next_if)]
+#![feature(partition_point)]
 
 extern crate test;
 
diff --git a/src/libcore/tests/slice.rs b/src/libcore/tests/slice.rs
index cd46117f763..fba73be92be 100644
--- a/src/libcore/tests/slice.rs
+++ b/src/libcore/tests/slice.rs
@@ -82,6 +82,46 @@ fn test_binary_search_implementation_details() {
 }
 
 #[test]
+fn test_partition_point() {
+    let b: [i32; 0] = [];
+    assert_eq!(b.partition_point(|&x| x < 5), 0);
+
+    let b = [4];
+    assert_eq!(b.partition_point(|&x| x < 3), 0);
+    assert_eq!(b.partition_point(|&x| x < 4), 0);
+    assert_eq!(b.partition_point(|&x| x < 5), 1);
+
+    let b = [1, 2, 4, 6, 8, 9];
+    assert_eq!(b.partition_point(|&x| x < 5), 3);
+    assert_eq!(b.partition_point(|&x| x < 6), 3);
+    assert_eq!(b.partition_point(|&x| x < 7), 4);
+    assert_eq!(b.partition_point(|&x| x < 8), 4);
+
+    let b = [1, 2, 4, 5, 6, 8];
+    assert_eq!(b.partition_point(|&x| x < 9), 6);
+
+    let b = [1, 2, 4, 6, 7, 8, 9];
+    assert_eq!(b.partition_point(|&x| x < 6), 3);
+    assert_eq!(b.partition_point(|&x| x < 5), 3);
+    assert_eq!(b.partition_point(|&x| x < 8), 5);
+
+    let b = [1, 2, 4, 5, 6, 8, 9];
+    assert_eq!(b.partition_point(|&x| x < 7), 5);
+    assert_eq!(b.partition_point(|&x| x < 0), 0);
+
+    let b = [1, 3, 3, 3, 7];
+    assert_eq!(b.partition_point(|&x| x < 0), 0);
+    assert_eq!(b.partition_point(|&x| x < 1), 0);
+    assert_eq!(b.partition_point(|&x| x < 2), 1);
+    assert_eq!(b.partition_point(|&x| x < 3), 1);
+    assert_eq!(b.partition_point(|&x| x < 4), 4);
+    assert_eq!(b.partition_point(|&x| x < 5), 4);
+    assert_eq!(b.partition_point(|&x| x < 6), 4);
+    assert_eq!(b.partition_point(|&x| x < 7), 4);
+    assert_eq!(b.partition_point(|&x| x < 8), 5);
+}
+
+#[test]
 fn test_iterator_nth() {
     let v: &[_] = &[0, 1, 2, 3, 4];
     for i in 0..v.len() {