X-Git-Url: http://ftp.safe.ca/?a=blobdiff_plain;f=include%2Flinux%2Flog2.h;h=25b808631cd92c50d10cf6a31b2d9b9942b62ac9;hb=f653398c86a1c104f0992bd788dd4bb065449be4;hp=1b8a2c1cb0e30e36ac1369372453dba264d4c3f9;hpb=1a06a52ee1b0cdb65222474ba6186f3991df68b0;p=safe%2Fjmp%2Flinux-2.6

diff --git a/include/linux/log2.h b/include/linux/log2.h
index 1b8a2c1..25b8086 100644
--- a/include/linux/log2.h
+++ b/include/linux/log2.h
@@ -63,6 +63,15 @@ unsigned long __roundup_pow_of_two(unsigned long n)
 	return 1UL << fls_long(n - 1);
 }
 
+/*
+ * round down to nearest power of two
+ */
+static inline __attribute__((const))
+unsigned long __rounddown_pow_of_two(unsigned long n)
+{
+	return 1UL << (fls_long(n) - 1);
+}
+
 /**
  * ilog2 - log of base 2 of 32-bit or a 64-bit unsigned value
  * @n - parameter
@@ -165,4 +174,36 @@ unsigned long __roundup_pow_of_two(unsigned long n)
 	__roundup_pow_of_two(n)			\
  )
 
+/**
+ * rounddown_pow_of_two - round the given value down to nearest power of two
+ * @n - parameter
+ *
+ * round the given value down to the nearest power of two
+ * - the result is undefined when n == 0
+ * - this can be used to initialise global variables from constant data
+ */
+#define rounddown_pow_of_two(n)			\
+(						\
+	__builtin_constant_p(n) ? (		\
+		(n == 1) ? 0 :			\
+		(1UL << ilog2(n))) :		\
+	__rounddown_pow_of_two(n)		\
+ )
+
+/**
+ * order_base_2 - calculate the (rounded up) base 2 order of the argument
+ * @n: parameter
+ *
+ * The first few values calculated by this routine:
+ *  ob2(0) = 0
+ *  ob2(1) = 0
+ *  ob2(2) = 1
+ *  ob2(3) = 2
+ *  ob2(4) = 2
+ *  ob2(5) = 3
+ *  ... and so on.
+ */
+
+#define order_base_2(n) ilog2(roundup_pow_of_two(n))
+
 #endif /* _LINUX_LOG2_H */