1 files changed, 101 insertions, 0 deletions
diff --git a/third_party/rust/getrandom/src/util.rs b/third_party/rust/getrandom/src/util.rs
new file mode 100644
index 0000000000..3162afad35
--- /dev/null
+++ b/third_party/rust/getrandom/src/util.rs
@@ -0,0 +1,101 @@
+// Copyright 2019 Developers of the Rand project.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// https://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or https://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+#![allow(dead_code)]
+use core::{
+    mem::MaybeUninit,
+    ptr,
+    sync::atomic::{AtomicUsize, Ordering::Relaxed},
+};
+
+// This structure represents a lazily initialized static usize value. Useful
+// when it is preferable to just rerun initialization instead of locking.
+// Both unsync_init and sync_init will invoke an init() function until it
+// succeeds, then return the cached value for future calls.
+//
+// Both methods support init() "failing". If the init() method returns UNINIT,
+// that value will be returned as normal, but will not be cached.
+//
+// Users should only depend on the _value_ returned by init() functions.
+// Specifically, for the following init() function:
+//      fn init() -> usize {
+//          a();
+//          let v = b();
+//          c();
+//          v
+//      }
+// the effects of c() or writes to shared memory will not necessarily be
+// observed and additional synchronization methods with be needed.
+pub struct LazyUsize(AtomicUsize);
+
+impl LazyUsize {
+    pub const fn new() -> Self {
+        Self(AtomicUsize::new(Self::UNINIT))
+    }
+
+    // The initialization is not completed.
+    pub const UNINIT: usize = usize::max_value();
+
+    // Runs the init() function at least once, returning the value of some run
+    // of init(). Multiple callers can run their init() functions in parallel.
+    // init() should always return the same value, if it succeeds.
+    pub fn unsync_init(&self, init: impl FnOnce() -> usize) -> usize {
+        // Relaxed ordering is fine, as we only have a single atomic variable.
+        let mut val = self.0.load(Relaxed);
+        if val == Self::UNINIT {
+            val = init();
+            self.0.store(val, Relaxed);
+        }
+        val
+    }
+}
+
+// Identical to LazyUsize except with bool instead of usize.
+pub struct LazyBool(LazyUsize);
+
+impl LazyBool {
+    pub const fn new() -> Self {
+        Self(LazyUsize::new())
+    }
+
+    pub fn unsync_init(&self, init: impl FnOnce() -> bool) -> bool {
+        self.0.unsync_init(|| init() as usize) != 0
+    }
+}
+
+/// Polyfill for `maybe_uninit_slice` feature's
+/// `MaybeUninit::slice_assume_init_mut`. Every element of `slice` must have
+/// been initialized.
+#[inline(always)]
+pub unsafe fn slice_assume_init_mut<T>(slice: &mut [MaybeUninit<T>]) -> &mut [T] {
+    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.
+    &mut *(slice as *mut [MaybeUninit<T>] as *mut [T])
+}
+
+#[inline]
+pub fn uninit_slice_fill_zero(slice: &mut [MaybeUninit<u8>]) -> &mut [u8] {
+    unsafe { ptr::write_bytes(slice.as_mut_ptr(), 0, slice.len()) };
+    unsafe { slice_assume_init_mut(slice) }
+}
+
+#[inline(always)]
+pub fn slice_as_uninit<T>(slice: &[T]) -> &[MaybeUninit<T>] {
+    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.
+    // There is no risk of writing a `MaybeUninit<T>` into the result since
+    // the result isn't mutable.
+    unsafe { &*(slice as *const [T] as *const [MaybeUninit<T>]) }
+}
+
+/// View an mutable initialized array as potentially-uninitialized.
+///
+/// This is unsafe because it allows assigning uninitialized values into
+/// `slice`, which would be undefined behavior.
+#[inline(always)]
+pub unsafe fn slice_as_uninit_mut<T>(slice: &mut [T]) -> &mut [MaybeUninit<T>] {
+    // SAFETY: `MaybeUninit<T>` is guaranteed to be layout-compatible with `T`.
+    &mut *(slice as *mut [T] as *mut [MaybeUninit<T>])
+}