Add a mean to unset a bit in the cache

library/stdarch/crates/std_detect/src/detect/cache.rs

@@ -23,6 +23,12 @@ const fn test_bit(x: u64, bit: u32) -> bool {
     x & (1 << bit) != 0
 }
 
+/// Unset the `bit of `x`.
+#[inline]
+const fn unset_bit(x: u64, bit: u32) -> u64 {
+    x & !(1 << bit)
+}
+
 /// Maximum number of features that can be cached.
 const CACHE_CAPACITY: u32 = 63;
 
@@ -63,6 +69,19 @@ impl Initializer {
         let v = self.0;
         self.0 = set_bit(v, bit);
     }
+
+    /// Unsets the `bit` of the cache.
+    #[inline]
+    pub(crate) fn unset(&mut self, bit: u32) {
+        // FIXME: this way of making sure that the cache is large enough is
+        // brittle.
+        debug_assert!(
+            bit < CACHE_CAPACITY,
+            "too many features, time to increase the cache size!"
+        );
+        let v = self.0;
+        self.0 = unset_bit(v, bit);
+    }
 }
 
 /// This global variable is a cache of the features supported by the CPU.