Loosen restrictions on CheckedNumeric bitwise operators

base/numerics/safe_math.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_NUMERICS_SAFE_MATH_H_
 #define BASE_NUMERICS_SAFE_MATH_H_
 
 #include <stddef.h>
 
 #include <limits>
 #include <type_traits>
 
 #include "base/numerics/safe_math_impl.h"
 
 namespace base {
 namespace internal {
 
 // CheckedNumeric implements all the logic and operators for detecting integer
 // boundary conditions such as overflow, underflow, and invalid conversions.
 // The CheckedNumeric type implicitly converts from floating point and integer
 // data types, and contains overloads for basic arithmetic operations (i.e.: +,
-// -, *, / for all types, % for integers, and &, |, ^ for unsigned integers).
+// -, *, / for all types and %, <<, >>, &, |, ^ for integers; additionally the
+// result of all bitwise logical operations is always promoted to an unsigned
+// CheckedNumeric type matching the width of the larger operand).
 //
 // You may also use one of the variadic convenience functions, which accept
 // standard arithmetic or CheckedNumeric types, perform arithmetic operations,
 // and return a CheckedNumeric result. The supported functions are:
 //  CheckAdd() - Addition.
 //  CheckSub() - Subtraction.
 //  CheckMul() - Multiplication.
 //  CheckDiv() - Division.
 //  CheckMod() - Modulous (integer only).
 //  CheckLsh() - Left integer shift (integer only).
@@ skipping 370 matching lines @@
 using internal::CheckMod;
 using internal::CheckLsh;
 using internal::CheckRsh;
 using internal::CheckAnd;
 using internal::CheckOr;
 using internal::CheckXor;
 
 }  // namespace base
 
 #endif  // BASE_NUMERICS_SAFE_MATH_H_