dfilter: Add binary arithmetic (add/subtract)

Add support for display filter binary addition and subtraction.

The grammar is intentionally kept simple for now. The use case
is to add a constant to a protocol field, or (maybe) add two
fields in an expression.

We use signed arithmetic with unsigned numbers, checking for
overflow and casting where necessary to do the conversion.
We could legitimately opt to use traditional modular arithmetic
instead (like C) and if it turns out that that is more useful for
some reason we may want to in the future.

Fixes #15504.

1 files changed, 3 insertions, 0 deletions

diff --git a/tools/checklicenses.py b/tools/checklicenses.py
index 7d04c49138..d6a0a37fef 100755
--- a/tools/checklicenses.py
+++ b/tools/checklicenses.py
@@ -149,6 +149,9 @@ PATH_SPECIFIC_ALLOWED_LICENSES = {
     '.gitlab/': [
         'UNKNOWN',
     ],
+    'wsutil/safe-math.h': [ # Public domain (CC0)
+        'UNKNOWN',
+    ],
 }
 
 def check_licenses(options, args):