Merge pull request #5662 from blubberdiblub/improve_mmu_mask_checks

Improve MMU mask checks

1 files changed, 22 insertions, 0 deletions

diff --git a/Source/Core/Common/BitUtils.h b/Source/Core/Common/BitUtils.h
index eacf6bf099..8d5398fb39 100644
--- a/Source/Core/Common/BitUtils.h
+++ b/Source/Core/Common/BitUtils.h
@@ -99,4 +99,26 @@ constexpr Result ExtractBits(const T src) noexcept
 
   return ExtractBits<T, Result>(src, begin, end);
 }
+
+///
+/// Verifies whether the supplied value is a valid bit mask of the form 0b00...0011...11.
+/// Both edge cases of all zeros and all ones are considered valid masks, too.
+///
+/// @param  mask The mask value to test for validity.
+///
+/// @tparam T    The type of the value.
+///
+/// @return A bool indicating whether the mask is valid.
+///
+template <typename T>
+constexpr bool IsValidLowMask(const T mask) noexcept
+{
+  static_assert(std::is_integral<T>::value, "Mask must be an integral type.");
+  static_assert(std::is_unsigned<T>::value, "Signed masks can introduce hard to find bugs.");
+
+  // Can be efficiently determined without looping or bit counting. It's the counterpart
+  // to https://graphics.stanford.edu/~seander/bithacks.html#DetermineIfPowerOf2
+  // and doesn't require special casing either edge case.
+  return (mask & (mask + 1)) == 0;
+}
 }  // namespace Common