1 files changed, 109 insertions, 0 deletions
diff --git a/servo/components/style/use_counters/mod.rs b/servo/components/style/use_counters/mod.rs
new file mode 100644
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+++ b/servo/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 https://mozilla.org/MPL/2.0/. */
+
+//! Various stuff for CSS property use counters.
+
+#[cfg(feature = "gecko")]
+use crate::gecko_bindings::sugar::ownership::{HasBoxFFI, HasFFI, HasSimpleFFI};
+use crate::properties::{CountedUnknownProperty, COUNTED_UNKNOWN_PROPERTY_COUNT};
+use crate::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 CountedUnknownPropertyUseCounters {
+    storage: [Cell<usize>; (COUNTED_UNKNOWN_PROPERTY_COUNT - 1 + BITS_PER_ENTRY) / BITS_PER_ENTRY],
+}
+
+/// 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],
+}
+
+macro_rules! property_use_counters_methods {
+    ($id: ident) => {
+        /// Returns the bucket a given property belongs in, and the bitmask for that
+        /// property.
+        #[inline(always)]
+        fn bucket_and_pattern(id: $id) -> (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 property ID has been parsed.
+        #[inline]
+        pub fn record(&self, id: $id) {
+            let (bucket, pattern) = Self::bucket_and_pattern(id);
+            let bucket = &self.storage[bucket];
+            bucket.set(bucket.get() | pattern)
+        }
+
+        /// Returns whether a given property ID has been recorded
+        /// earlier.
+        #[inline]
+        pub fn recorded(&self, id: $id) -> 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())
+            }
+        }
+    };
+}
+
+impl CountedUnknownPropertyUseCounters {
+    property_use_counters_methods!(CountedUnknownProperty);
+}
+
+impl NonCustomPropertyUseCounters {
+    property_use_counters_methods!(NonCustomPropertyId);
+}
+
+/// 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,
+    /// The counters for css properties which we haven't implemented yet.
+    pub counted_unknown_properties: CountedUnknownPropertyUseCounters,
+}
+
+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);
+        self.counted_unknown_properties
+            .merge(&other.counted_unknown_properties);
+    }
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasFFI for UseCounters {
+    type FFIType = crate::gecko_bindings::structs::StyleUseCounters;
+}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasSimpleFFI for UseCounters {}
+
+#[cfg(feature = "gecko")]
+unsafe impl HasBoxFFI for UseCounters {}