Add soa crate

crates/soa/src/soa_slice.rs

@@ -0,0 +1,112 @@
+use core::fmt;
+use core::iter::Map;
+
+use crate::soa_index::Index;
+
+/// A slice into an array of values, based
+/// on an offset into the array rather than a pointer.
+///
+/// Unlike a Rust slice, this is a u32 offset
+/// rather than a pointer, and the length is u16.
+pub struct Slice<T> {
+    pub start: u32,
+    pub length: u16,
+    _marker: core::marker::PhantomData<T>,
+}
+
+impl<T> fmt::Debug for Slice<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(
+            f,
+            "Slice {{ start: {}, length: {} }}",
+            self.start, self.length
+        )
+    }
+}
+
+// derive of copy and clone does not play well with PhantomData
+
+impl<T> Copy for Slice<T> {}
+
+impl<T> Clone for Slice<T> {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl<T> Default for Slice<T> {
+    fn default() -> Self {
+        Self::empty()
+    }
+}
+
+impl<T> Slice<T> {
+    pub fn empty() -> Self {
+        Self {
+            start: 0,
+            length: 0,
+            _marker: Default::default(),
+        }
+    }
+
+    pub fn get_slice<'a>(&self, slice: &'a [T]) -> &'a [T] {
+        &slice[self.indices()]
+    }
+
+    pub fn get_slice_mut<'a>(&self, slice: &'a mut [T]) -> &'a mut [T] {
+        &mut slice[self.indices()]
+    }
+
+    #[inline(always)]
+    pub fn indices(&self) -> core::ops::Range<usize> {
+        self.start as usize..(self.start as usize + self.length as usize)
+    }
+
+    pub const fn len(&self) -> usize {
+        self.length as usize
+    }
+
+    pub const fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    pub const fn new(start: u32, length: u16) -> Self {
+        Self {
+            start,
+            length,
+            _marker: std::marker::PhantomData,
+        }
+    }
+
+    pub fn extend_new(vec: &mut Vec<T>, it: impl IntoIterator<Item = T>) -> Self {
+        let start = vec.len();
+
+        vec.extend(it);
+
+        let end = vec.len();
+
+        Self::new(start as u32, (end - start) as u16)
+    }
+}
+
+impl<T> IntoIterator for Slice<T> {
+    type Item = Index<T>;
+
+    #[allow(clippy::type_complexity)]
+    type IntoIter = Map<core::ops::Range<u32>, fn(u32) -> Self::Item>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        (self.start..(self.start + self.length as u32)).map(u32_to_index)
+    }
+}
+
+fn u32_to_index<T>(i: u32) -> Index<T> {
+    Index {
+        index: i,
+        _marker: core::marker::PhantomData,
+    }
+}
+
+pub trait GetSlice<T> {
+    fn get_slice(&self, slice: Slice<T>) -> &[T];
+}