Fix MPMC size asserts

Author: chemicstry

src/mpmc.rs

@@ -122,6 +122,7 @@ pub type Q32<T> = MpMcQueue<T, 32>;
 pub type Q64<T> = MpMcQueue<T, 64>;
 
 /// MPMC queue with a capacity for N elements
+/// N must be a power of 2
 /// The max value of N is u8::MAX - 1 if `mpmc_large` feature is not enabled.
 pub struct MpMcQueue<T, const N: usize> {
     buffer: UnsafeCell<[Cell<T>; N]>,
@@ -138,7 +139,8 @@ impl<T, const N: usize> MpMcQueue<T, N> {
     /// Creates an empty queue
     pub const fn new() -> Self {
         // Const assert
-        crate::sealed::greater_than_0::<N>();
+        crate::sealed::greater_than_1::<N>();
+        crate::sealed::power_of_two::<N>();
 
         // Const assert on size.
         Self::ASSERT[!(N < (IntSize::MAX as usize)) as usize];

src/sealed.rs

@@ -64,6 +64,13 @@ pub(crate) const fn greater_than_1<const N: usize>() {
     Assert::<N, 1>::GREATER;
 }
 
+#[allow(dead_code)]
+#[allow(path_statements)]
+pub(crate) const fn power_of_two<const N: usize>() {
+    Assert::<N, 0>::GREATER;
+    Assert::<N, 0>::POWER_OF_TWO;
+}
+
 #[allow(dead_code)]
 /// Const assert hack
 pub struct Assert<const L: usize, const R: usize>;
@@ -87,4 +94,7 @@ impl<const L: usize, const R: usize> Assert<L, R> {
 
     /// Const assert hack
     pub const LESS: usize = R - L - 1;
+
+    /// Const assert hack
+    pub const POWER_OF_TWO: usize = 0 - (L & (L - 1));
 }