wip between-user padding

src/padding.zig

@@ -0,0 +1,29 @@
+const std = @import("std");
+
+// rounds up a u12 to the nearest factor of 4 and returns the difference
+// (padding)
+pub fn roundUp4Padding(comptime T: type, n: T) T {
+    return roundUp4(T, n) - n;
+}
+
+// rounds up a u12 to the nearest factor of 4.
+pub fn roundUp4(comptime T: type, n: T) T {
+    return ((n + 3) & ~@as(T, 3));
+}
+
+const testing = std.testing;
+
+test "padding" {
+    try testing.expectEqual(roundUp4Padding(u12, 0), 0);
+    try testing.expectEqual(roundUp4Padding(u12, 1), 3);
+    try testing.expectEqual(roundUp4Padding(u12, 2), 2);
+    try testing.expectEqual(roundUp4Padding(u12, 3), 1);
+    try testing.expectEqual(roundUp4Padding(u12, 4), 0);
+    try testing.expectEqual(roundUp4Padding(u12, 40), 0);
+    try testing.expectEqual(roundUp4Padding(u12, 41), 3);
+    try testing.expectEqual(roundUp4Padding(u12, 42), 2);
+    try testing.expectEqual(roundUp4Padding(u12, 43), 1);
+    try testing.expectEqual(roundUp4Padding(u12, 44), 0);
+    try testing.expectEqual(roundUp4Padding(u12, 4091), 1);
+    try testing.expectEqual(roundUp4Padding(u12, 4092), 0);
+}