List.repeat in zig

compiler/builtins/bitcode/src/list.zig

@@ -7,6 +7,9 @@ const Allocator = mem.Allocator;
 const EqFn = fn (?[*]u8, ?[*]u8) callconv(.C) bool;
 const Opaque = ?[*]u8;
 
+const Inc = fn (?[*]u8) callconv(.C) void;
+const Dec = fn (?[*]u8) callconv(.C) void;
+
 pub const RocList = extern struct {
     bytes: ?[*]u8,
     length: usize,
@@ -278,3 +281,30 @@ pub fn listContains(list: RocList, key: Opaque, key_width: usize, is_eq: EqFn) c
 
     return false;
 }
+
+pub fn listRepeat(count: usize, alignment: usize, element: Opaque, element_width: usize, inc_n_element: Inc) callconv(.C) RocList {
+    if (count == 0) {
+        return RocList.empty();
+    }
+
+    const allocator = std.heap.c_allocator;
+    var output = RocList.allocate(allocator, alignment, count, element_width);
+
+    if (output.bytes) |target_ptr| {
+        var i: usize = 0;
+        const source = element orelse unreachable;
+        while (i < count) : (i += 1) {
+            @memcpy(target_ptr + i * element_width, source, element_width);
+        }
+
+        // TODO do all increments at once!
+        i = 0;
+        while (i < count) : (i += 1) {
+            inc_n_element(element);
+        }
+
+        return output;
+    } else {
+        unreachable;
+    }
+}

compiler/builtins/bitcode/src/main.zig

@@ -14,6 +14,7 @@ comptime {
     exportListFn(list.listKeepOks, "keep_oks");
     exportListFn(list.listKeepErrs, "keep_errs");
     exportListFn(list.listContains, "contains");
+    exportListFn(list.listRepeat, "repeat");
 }
 
 // Dict Module