1 files changed, 88 insertions, 0 deletions
diff --git a/components/style/use_counters/mod.rs b/components/style/use_counters/mod.rs
new file mode 100644
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+++ b/components/style/use_counters/mod.rs
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+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! Various stuff for CSS property use counters.
+
+#[cfg(feature = "gecko")]
+use gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
+use properties::{NonCustomPropertyId, NON_CUSTOM_PROPERTY_ID_COUNT};
+use std::cell::Cell;
+
+#[cfg(target_pointer_width = "64")]
+const BITS_PER_ENTRY: usize = 64;
+
+#[cfg(target_pointer_width = "32")]
+const BITS_PER_ENTRY: usize = 32;
+
+/// One bit per each non-custom CSS property.
+#[derive(Default)]
+pub struct NonCustomPropertyUseCounters {
+    storage: [Cell<usize>; (NON_CUSTOM_PROPERTY_ID_COUNT - 1 + BITS_PER_ENTRY) / BITS_PER_ENTRY],
+}
+
+impl NonCustomPropertyUseCounters {
+    /// Returns the bucket a given property belongs in, and the bitmask for that
+    /// property.
+    #[inline(always)]
+    fn bucket_and_pattern(id: NonCustomPropertyId) -> (usize, usize) {
+        let bit = id.bit();
+        let bucket = bit / BITS_PER_ENTRY;
+        let bit_in_bucket = bit % BITS_PER_ENTRY;
+        (bucket, 1 << bit_in_bucket)
+    }
+
+    /// Record that a given non-custom property ID has been parsed.
+    #[inline]
+    pub fn record(&self, id: NonCustomPropertyId) {
+        let (bucket, pattern) = Self::bucket_and_pattern(id);
+        let bucket = &self.storage[bucket];
+        bucket.set(bucket.get() | pattern)
+    }
+
+    /// Returns whether a given non-custom property ID has been recorded
+    /// earlier.
+    #[inline]
+    pub fn recorded(&self, id: NonCustomPropertyId) -> bool {
+        let (bucket, pattern) = Self::bucket_and_pattern(id);
+        self.storage[bucket].get() & pattern != 0
+    }
+
+    /// Merge `other` into `self`.
+    #[inline]
+    fn merge(&self, other: &Self) {
+        for (bucket, other_bucket) in self.storage.iter().zip(other.storage.iter()) {
+            bucket.set(bucket.get() | other_bucket.get())
+        }
+    }
+}
+
+/// The use-counter data related to a given document we want to store.
+#[derive(Default)]
+pub struct UseCounters {
+    /// The counters for non-custom properties that have been parsed in the
+    /// document's stylesheets.
+    pub non_custom_properties: NonCustomPropertyUseCounters,
+}
+
+impl UseCounters {
+    /// Merge the use counters.
+    ///
+    /// Used for parallel parsing, where we parse off-main-thread.
+    #[inline]
+    pub fn merge(&self, other: &Self) {
+        self.non_custom_properties
+            .merge(&other.non_custom_properties)
+    }
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasFFI for UseCounters {
+    type FFIType = ::gecko_bindings::structs::StyleUseCounters;
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasSimpleFFI for UseCounters {}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasBoxFFI for UseCounters {}