Prepare hashbrown for inclusion in the standard library

Author: Amanieu

Cargo.toml

@@ -11,13 +11,15 @@ categories = ["data-structures", "no-std"]
 exclude = [".travis.yml", "bors.toml"]
 
 [dependencies]
-byteorder = { version = "1.0", default-features = false }
-scopeguard = { version = "0.3", default-features = false }
-
 # For external trait impls
 rayon = { version = "1.0", optional = true }
 serde = { version = "1.0.25", default-features = false, optional = true }
 
+# When built as part of libstd
+core = { version = "1.0.0", optional = true, package = "rustc-std-workspace-core" }
+compiler_builtins = { version = "0.1.2", optional = true }
+alloc = { version = "1.0.0", optional = true, package = "rustc-std-workspace-alloc" }
+
 [dev-dependencies]
 lazy_static = "~1.2"
 rand = "0.5.1"
@@ -27,3 +29,4 @@ serde_test = "1.0"
 
 [features]
 nightly = []
+rustc-dep-of-std = ["nightly", "core", "compiler_builtins", "alloc"]

src/fx.rs

@@ -5,8 +5,6 @@ use core::hash::{BuildHasherDefault, Hasher};
 use core::mem::size_of;
 use core::ops::BitXor;
 
-use byteorder::{ByteOrder, NativeEndian};
-
 /// Type alias for a `HashBuilder` using the `fx` hash algorithm.
 pub type FxHashBuilder = BuildHasherDefault<FxHasher>;
 
@@ -47,23 +45,29 @@ impl FxHasher {
 impl Hasher for FxHasher {
     #[inline]
     fn write(&mut self, mut bytes: &[u8]) {
-        #[cfg(target_pointer_width = "32")]
-        let read_usize = |bytes| NativeEndian::read_u32(bytes);
-        #[cfg(target_pointer_width = "64")]
-        let read_usize = |bytes| NativeEndian::read_u64(bytes);
+        macro_rules! read_bytes {
+            ($ty:ty, $src:expr) => {{
+                assert!(size_of::<$ty>() <= $src.len());
+                let mut data: $ty = 0;
+                unsafe {
+                    $src.as_ptr().copy_to_nonoverlapping(&mut data as *mut $ty as *mut u8, size_of::<$ty>());
+                }
+                data
+            }};
+        }
 
         let mut hash = FxHasher { hash: self.hash };
         assert!(size_of::<usize>() <= 8);
         while bytes.len() >= size_of::<usize>() {
-            hash.add_to_hash(read_usize(bytes) as usize);
+            hash.add_to_hash(read_bytes!(usize, bytes) as usize);
             bytes = &bytes[size_of::<usize>()..];
         }
         if (size_of::<usize>() > 4) && (bytes.len() >= 4) {
-            hash.add_to_hash(NativeEndian::read_u32(bytes) as usize);
+            hash.add_to_hash(read_bytes!(u32, bytes) as usize);
             bytes = &bytes[4..];
         }
         if (size_of::<usize>() > 2) && bytes.len() >= 2 {
-            hash.add_to_hash(NativeEndian::read_u16(bytes) as usize);
+            hash.add_to_hash(read_bytes!(u16, bytes) as usize);
             bytes = &bytes[2..];
         }
         if (size_of::<usize>() > 1) && bytes.len() >= 1 {

src/lib.rs

@@ -25,18 +25,16 @@
 #![warn(missing_docs)]
 
 #[cfg(test)]
-#[macro_use]
+#[cfg_attr(feature = "rayon", macro_use)]
 extern crate std;
 #[cfg(test)]
 extern crate rand;
 
 #[cfg(feature = "nightly")]
 #[cfg_attr(test, macro_use)]
 extern crate alloc;
-extern crate byteorder;
 #[cfg(feature = "rayon")]
 extern crate rayon;
-extern crate scopeguard;
 #[cfg(feature = "serde")]
 extern crate serde;
 #[cfg(not(feature = "nightly"))]
@@ -51,11 +49,16 @@ mod fx;
 mod map;
 mod raw;
 mod set;
+#[cfg(feature = "rustc-dep-of-std")]
+mod rustc_entry;
 
 pub mod hash_map {
     //! A hash map implemented with quadratic probing and SIMD lookup.
     pub use map::*;
 
+    #[cfg(feature = "rustc-dep-of-std")]
+    pub use rustc_entry::*;
+
     #[cfg(feature = "rayon")]
     /// [rayon]-based parallel iterator types for hash maps.
     /// You will rarely need to interact with it directly unless you have need