WIP: list assignment

nac3core/irrt/irrt/list.hpp

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <irrt/debug.hpp>
+#include <irrt/exception.hpp>
 #include <irrt/int_types.hpp>
 #include <irrt/slice.hpp>
 
@@ -16,4 +18,42 @@ template <typename SizeT> struct List
     uint8_t *items;
     SizeT len;
 };
+
+namespace list
+{
+template <typename SizeT> void range_assign(List<SizeT> *dst, SizeT itemsize, Range<SizeT> *range, List<SizeT> *src)
+{
+    debug_assert(range->step != 0);
+    SizeT assign_len = range->len();
+
+    if (assign_len < src->len)
+    {
+        // Encountered things like
+        // ```
+        // xs = [1, 2, 3, 4, 5]
+        // xs[1:3] = [999, 1000, 1001, 1002] # Note that step has to be 1.
+        // xs = [1, 999, 1000, 1001, 1002, 4, 5] # xs is longer
+        // ```
+        //
+        // We do not support extending lists since that requires allocation.
+        raise_exception(SizeT, EXN_VALUE_ERROR,
+                        "List assignment does not support list extension. Attempting to assign {0} item(s) into a "
+                        "space of {1} item(s).",
+                        src->len, assign_len, NO_PARAM);
+    }
+
+    if (range->step == 1)
+    {
+        // Assigning into a contiguous region. Optimized with memmove.
+
+        uint8_t* p1 = dst->items + range->start * itemsize;
+        uint8_t* p2 = dst->items + range->start * itemsize + assign_len * itemsize;
+
+        __builtin_memmove(cursor, src->items, assign_len * itemsize);
+        cursor += range_len * itemsize;
+
+        __builtin_memmove(cursor, );
+    }
+}
+} // namespace list
 } // namespace