1 files changed, 60 insertions, 0 deletions
diff --git a/third_party/rust/minimal-lexical/src/mask.rs b/third_party/rust/minimal-lexical/src/mask.rs
new file mode 100644
index 0000000000..1957c8be03
--- /dev/null
+++ b/third_party/rust/minimal-lexical/src/mask.rs
@@ -0,0 +1,60 @@
+//! Utilities to generate bitmasks.
+
+#![doc(hidden)]
+
+/// Generate a bitwise mask for the lower `n` bits.
+///
+/// # Examples
+///
+/// ```rust
+/// # use minimal_lexical::mask::lower_n_mask;
+/// # pub fn main() {
+/// assert_eq!(lower_n_mask(2), 0b11);
+/// # }
+/// ```
+#[inline]
+pub fn lower_n_mask(n: u64) -> u64 {
+    debug_assert!(n <= 64, "lower_n_mask() overflow in shl.");
+
+    match n == 64 {
+        // u64::MAX for older Rustc versions.
+        true => 0xffff_ffff_ffff_ffff,
+        false => (1 << n) - 1,
+    }
+}
+
+/// Calculate the halfway point for the lower `n` bits.
+///
+/// # Examples
+///
+/// ```rust
+/// # use minimal_lexical::mask::lower_n_halfway;
+/// # pub fn main() {
+/// assert_eq!(lower_n_halfway(2), 0b10);
+/// # }
+/// ```
+#[inline]
+pub fn lower_n_halfway(n: u64) -> u64 {
+    debug_assert!(n <= 64, "lower_n_halfway() overflow in shl.");
+
+    match n == 0 {
+        true => 0,
+        false => nth_bit(n - 1),
+    }
+}
+
+/// Calculate a scalar factor of 2 above the halfway point.
+///
+/// # Examples
+///
+/// ```rust
+/// # use minimal_lexical::mask::nth_bit;
+/// # pub fn main() {
+/// assert_eq!(nth_bit(2), 0b100);
+/// # }
+/// ```
+#[inline]
+pub fn nth_bit(n: u64) -> u64 {
+    debug_assert!(n < 64, "nth_bit() overflow in shl.");
+    1 << n
+}