1 files changed, 46 insertions, 0 deletions
diff --git a/library/portable-simd/crates/core_simd/src/lane_count.rs b/library/portable-simd/crates/core_simd/src/lane_count.rs
new file mode 100644
index 000000000..63723e2ec
--- /dev/null
+++ b/library/portable-simd/crates/core_simd/src/lane_count.rs
@@ -0,0 +1,46 @@
+mod sealed {
+    pub trait Sealed {}
+}
+use sealed::Sealed;
+
+/// Specifies the number of lanes in a SIMD vector as a type.
+pub struct LaneCount<const LANES: usize>;
+
+impl<const LANES: usize> LaneCount<LANES> {
+    /// The number of bytes in a bitmask with this many lanes.
+    pub const BITMASK_LEN: usize = (LANES + 7) / 8;
+}
+
+/// Statically guarantees that a lane count is marked as supported.
+///
+/// This trait is *sealed*: the list of implementors below is total.
+/// Users do not have the ability to mark additional `LaneCount<N>` values as supported.
+/// Only SIMD vectors with supported lane counts are constructable.
+pub trait SupportedLaneCount: Sealed {
+    #[doc(hidden)]
+    type BitMask: Copy + Default + AsRef<[u8]> + AsMut<[u8]>;
+}
+
+impl<const LANES: usize> Sealed for LaneCount<LANES> {}
+
+impl SupportedLaneCount for LaneCount<1> {
+    type BitMask = [u8; 1];
+}
+impl SupportedLaneCount for LaneCount<2> {
+    type BitMask = [u8; 1];
+}
+impl SupportedLaneCount for LaneCount<4> {
+    type BitMask = [u8; 1];
+}
+impl SupportedLaneCount for LaneCount<8> {
+    type BitMask = [u8; 1];
+}
+impl SupportedLaneCount for LaneCount<16> {
+    type BitMask = [u8; 2];
+}
+impl SupportedLaneCount for LaneCount<32> {
+    type BitMask = [u8; 4];
+}
+impl SupportedLaneCount for LaneCount<64> {
+    type BitMask = [u8; 8];
+}