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-rw-r--r--include/linux/log2.h34
1 files changed, 34 insertions, 0 deletions
diff --git a/include/linux/log2.h b/include/linux/log2.h
index 1aec01365ed4..83a4a3ca3e8a 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -220,4 +220,38 @@ int __order_base_2(unsigned long n)
ilog2((n) - 1) + 1) : \
__order_base_2(n) \
)
+
+static inline __attribute__((const))
+int __bits_per(unsigned long n)
+{
+ if (n < 2)
+ return 1;
+ if (is_power_of_2(n))
+ return order_base_2(n) + 1;
+ return order_base_2(n);
+}
+
+/**
+ * bits_per - calculate the number of bits required for the argument
+ * @n: parameter
+ *
+ * This is constant-capable and can be used for compile time
+ * initializations, e.g bitfields.
+ *
+ * The first few values calculated by this routine:
+ * bf(0) = 1
+ * bf(1) = 1
+ * bf(2) = 2
+ * bf(3) = 2
+ * bf(4) = 3
+ * ... and so on.
+ */
+#define bits_per(n) \
+( \
+ __builtin_constant_p(n) ? ( \
+ ((n) == 0 || (n) == 1) \
+ ? 1 : ilog2(n) + 1 \
+ ) : \
+ __bits_per(n) \
+)
#endif /* _LINUX_LOG2_H */