1 files changed, 85 insertions, 0 deletions
diff --git a/rendy-memory/src/mapping/range.rs b/rendy-memory/src/mapping/range.rs
new file mode 100644
index 0000000..f4c49be
--- /dev/null
+++ b/rendy-memory/src/mapping/range.rs
@@ -0,0 +1,85 @@
+use {
+    crate::util::fits_usize,
+    std::{
+        mem::{align_of, size_of},
+        ops::Range,
+        ptr::NonNull,
+        slice::{from_raw_parts, from_raw_parts_mut},
+    },
+};
+
+/// Get sub-range of memory mapping.
+/// `range` and `fitting` are in memory object space.
+/// `ptr` points to the `range.start` offset from memory origin.
+/// returns pointer to `fitting.start` offset from memory origin
+/// if `fitting` is contained in `range`.
+pub(crate) fn mapped_sub_range(
+    ptr: NonNull<u8>,
+    range: Range<u64>,
+    fitting: Range<u64>,
+) -> Option<NonNull<u8>> {
+    assert!(
+        range.start < range.end,
+        "Memory mapping region must have valid size"
+    );
+    assert!(
+        fitting.start < fitting.end,
+        "Memory mapping region must have valid size"
+    );
+    assert!(fits_usize(range.end - range.start));
+    assert!(usize::max_value() - (range.end - range.start) as usize >= ptr.as_ptr() as usize);
+
+    if fitting.start < range.start || fitting.end > range.end {
+        None
+    } else {
+        Some(unsafe {
+            // for x > 0 and y >= 0: x + y > 0. No overflow due to checks above.
+            NonNull::new_unchecked(
+                (ptr.as_ptr() as usize + (fitting.start - range.start) as usize) as *mut u8,
+            )
+        })
+    }
+}
+
+/// # Safety
+///
+/// User must ensure that:
+/// * this function won't create aliasing slices.
+/// * returned slice doesn't outlive mapping.
+/// * `T` Must be plain-old-data type compatible with data in mapped region.
+pub(crate) unsafe fn mapped_slice_mut<'a, T>(ptr: NonNull<u8>, size: usize) -> &'a mut [T] {
+    assert_eq!(
+        size % size_of::<T>(),
+        0,
+        "Range length must be multiple of element size"
+    );
+    let offset = ptr.as_ptr() as usize;
+    assert_eq!(
+        offset % align_of::<T>(),
+        0,
+        "Range offset must be multiple of element alignment"
+    );
+    assert!(usize::max_value() - size >= ptr.as_ptr() as usize);
+    from_raw_parts_mut(ptr.as_ptr() as *mut T, size)
+}
+
+/// # Safety
+///
+/// User must ensure that:
+/// * returned slice doesn't outlive mapping.
+/// * `T` Must be plain-old-data type compatible with data in mapped region.
+pub(crate) unsafe fn mapped_slice<'a, T>(ptr: NonNull<u8>, size: usize) -> &'a [T] {
+    assert_eq!(
+        size % size_of::<T>(),
+        0,
+        "Range length must be multiple of element size"
+    );
+    let offset = ptr.as_ptr() as usize;
+    assert_eq!(
+        offset % align_of::<T>(),
+        0,
+        "Range offset must be multiple of element alignment"
+    );
+    assert!(usize::max_value() - size >= ptr.as_ptr() as usize);
+    from_raw_parts(ptr.as_ptr() as *const T, size)
+}