rusticl/util: add MultiValProperties

Acked-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36007>

src/gallium/frontends/rusticl/util/properties.rs

@@ -84,3 +84,126 @@ impl<T> Properties<T> {
         &self.props
     }
 }
+
+#[derive(Default)]
+pub struct MultiValProperties<T> {
+    props: Vec<T>,
+    keys_pos: Vec<(usize, usize)>,
+}
+
+/// This encapsulates a C property array, where the list is 0 terminated and keys might contain
+/// multiple values.
+impl<T> MultiValProperties<T> {
+    /// Creates a Properties object copying from the supplied pointer.
+    ///
+    /// It returns `None` if any property is found twice.
+    ///
+    /// If `p` is null the saved list of properties will be empty. Otherwise it will be 0
+    /// terminated.
+    ///
+    /// # Safety
+    ///
+    /// Besides `p` being valid to be dereferenced, it also needs to point to a `T::default()`
+    /// terminated array of `T`. In addition to that, keys that contain list of values also need to
+    /// be `T::default()` terminated.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let raw_props = [
+    ///     KEY_A, VAL_A,
+    ///     MULTI_VAL_KEY_A, VAL_C, VAL_D, VAL_E, 0,
+    ///     KEY_B, VAL_B,
+    ///     0,
+    /// ];
+    /// let props = MultiValProperties::new(&raw_props, &[MULTI_VAL_KEY_A]).unwrap();
+    /// assert_eq!(props.get(KEY_B), Some(&[VAL_B]));
+    /// assert_eq!(props.get(MULTI_VAL_KEY_A), SOME(&[VAL_C, VAL_D, VAL_E]));
+    /// ```
+    pub unsafe fn new(mut p: *const T, multi_val_keys: &[T]) -> Option<Self>
+    where
+        T: Copy + Default + PartialEq,
+    {
+        let mut res = Self::default();
+        if !p.is_null() {
+            // SAFETY: Reading add offset 0 is safe according to the requirements of this function.
+            let mut val = unsafe { p.read_and_advance() };
+            while val != T::default() {
+                if res.get(val).is_some() {
+                    return None;
+                }
+
+                let start = res.props.len();
+                res.props.push(val);
+
+                let mut end = start + 1;
+                if multi_val_keys.contains(&val) {
+                    loop {
+                        // SAFETY: For a multi-value key it's safe to read until we hit a
+                        //         T::default()
+                        val = unsafe { p.read_and_advance() };
+                        res.props.push(val);
+
+                        // We break after pushing the value in order to keep the original values
+                        // intact.
+                        if val == T::default() {
+                            break;
+                        }
+                        end += 1;
+                    }
+                } else {
+                    // SAFETY: It's safe to read key-value pairs.
+                    res.props.push(unsafe { p.read_and_advance() });
+                    end += 1;
+                }
+
+                res.keys_pos.push((start, end));
+                // SAFETY: it's either a new key or T::default, therefore safe to read.
+                val = unsafe { p.read_and_advance() };
+            }
+
+            // terminate the array
+            res.props.push(T::default());
+        }
+
+        Some(res)
+    }
+
+    /// Returns the values for the given `key` if existent.
+    pub fn get(&self, key: T) -> Option<&[T]>
+    where
+        T: Copy + PartialEq,
+    {
+        // Property lists are expected to be small, so we can do a lookup each time without hurting
+        // perf too much.
+        self.iter().find_map(|(k, v)| (k == key).then_some(v))
+    }
+
+    /// Returns true when there is no property available.
+    pub fn is_empty(&self) -> bool {
+        self.props.len() <= 1
+    }
+
+    pub fn iter(&self) -> impl Iterator<Item = (T, &[T])>
+    where
+        T: Copy,
+    {
+        self.keys_pos.iter().map(|&(start, end)| {
+            let key = self.props[start];
+            (key, &self.props[start + 1..end])
+        })
+    }
+
+    /// Returns the amount of key/values pairs available.
+    pub fn len(&self) -> usize {
+        self.keys_pos.len()
+    }
+
+    /// Returns a slice to the raw buffer.
+    ///
+    /// It will return an empty slice if `self` was created with a null pointer. A `T::default()`
+    /// terminated one otherwise.
+    pub fn as_raw_slice(&self) -> &[T] {
+        &self.props
+    }
+}