From a088f105aa2e099ba027e47f9bc29c30b06b416e Mon Sep 17 00:00:00 2001
From: Oliver Schneider <git-spam-no-reply9815368754983@oli-obk.de>
Date: Mon, 20 Jun 2016 17:52:14 +0200
Subject: [PATCH] add a comment explaining the magic numbers

---
 src/primval.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/primval.rs b/src/primval.rs
index 586aaeee4e92..29d79abbbfc4 100644
--- a/src/primval.rs
+++ b/src/primval.rs
@@ -69,6 +69,8 @@ pub fn binary_op<'tcx>(bin_op: mir::BinOp, left: PrimVal, right: PrimVal) -> Eva
     match bin_op {
         // can have rhs with a different numeric type
         Shl | Shr => {
+            // these numbers are the maximum number of bits a bitshift rhs could possibly have
+            // e.g. u16 can be bitshifted by 0..16, so 2^4 - 1 is the largest possible bitshift
             let mask_bits = match left {
                 I8(_) => 3,
                 I16(_) => 4,