[PATCH] checkpatch: Try to avoid mask and shift errors

[Joe Perches <joe@perches.com>]

Shift has a higher precedence that mask so warn
when a mask then shift operation is done without
parentheses around the mask.

This test works well for a right shift, but the
left shift is pretty commonly done correctly so
only warn on the right shift.

Signed-off-by: Joe Perches <joe@perches.com>
---
 scripts/checkpatch.pl | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index d94f5d8..9b474d5 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4478,6 +4478,14 @@ sub process {
 			}
 		}
 
+# check for mask then right shift without a parentheses
+		if ($^V && $^V ge 5.10.0 &&
+		    $line =~ /$LvalOrFunc\s*\&\s*($LvalOrFunc)\s*>>/ &&
+		    $4 !~ /^\&/) { # $LvalOrFunc may be &foo, ignore if so
+			WARN("MASK_THEN_SHIFT",
+			     "Possible precedence defect with mask then right shift - may need parentheses\n" . $herecurr);
+		}
+
 # check for bad placement of section $InitAttribute (e.g.: __initdata)
 		if ($line =~ /(\b$InitAttribute\b)/) {
 			my $attr = $1;