[PATCH rdma-next 08/12] overflow.h: Add arithmetic shift helper

[Leon Romanovsky <leon@kernel.org>]

From: Leon Romanovsky <leonro@mellanox.com>

Add shift_overflow() helper to help driver authors to ensure that
shift operand doesn't cause to overflow, which is very common pattern
for RDMA drivers.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
---
 include/linux/overflow.h | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 8712ff70995f..2a3395248e94 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -202,6 +202,29 @@

 #endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */

+/**
+ * shift_overflow() - Peform shift operation with overflow check
+ * @a: value to be shifted
+ * @b: shift operand
+ *
+ * Checks if a << b will overflow
+ *
+ * Returns: result of shift for no overflow or SIZE_MAX for overflow
+ */
+static inline __must_check size_t shift_overflow(size_t a, size_t b)
+{
+	size_t c, res;
+
+	if (b >= sizeof(size_t) * BITS_PER_BYTE)
+		return SIZE_MAX;
+
+	c = (size_t)1 << b;
+	if (check_mul_overflow(a, c, &res))
+		return SIZE_MAX;
+
+	return res;
+}
+
 /**
  * array_size() - Calculate size of 2-dimensional array.
  *
--
2.14.4