bitops: Ensure the compile time HWEIGHT is only used for such
[linux-2.6.git] / include / linux / bitops.h
index ba0fd1e..25b8b2f 100644 (file)
@@ -45,19 +45,30 @@ static inline unsigned long hweight_long(unsigned long w)
        return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
 }
 
-#define HWEIGHT8(w)                    \
-      (        (!!((w) & (1ULL << 0))) +       \
-       (!!((w) & (1ULL << 1))) +       \
-       (!!((w) & (1ULL << 2))) +       \
-       (!!((w) & (1ULL << 3))) +       \
-       (!!((w) & (1ULL << 4))) +       \
-       (!!((w) & (1ULL << 5))) +       \
-       (!!((w) & (1ULL << 6))) +       \
+/*
+ * Clearly slow versions of the hweightN() functions, their benefit is
+ * of course compile time evaluation of constant arguments.
+ */
+#define HWEIGHT8(w)                                    \
+      (        BUILD_BUG_ON_ZERO(!__builtin_constant_p(w)) +   \
+       (!!((w) & (1ULL << 0))) +                       \
+       (!!((w) & (1ULL << 1))) +                       \
+       (!!((w) & (1ULL << 2))) +                       \
+       (!!((w) & (1ULL << 3))) +                       \
+       (!!((w) & (1ULL << 4))) +                       \
+       (!!((w) & (1ULL << 5))) +                       \
+       (!!((w) & (1ULL << 6))) +                       \
        (!!((w) & (1ULL << 7))) )
 
-#define HWEIGHT16(w) (HWEIGHT8(w)  + HWEIGHT8(w >> 8))
-#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16(w >> 16))
-#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32(w >> 32))
+#define HWEIGHT16(w) (HWEIGHT8(w)  + HWEIGHT8((w) >> 8))
+#define HWEIGHT32(w) (HWEIGHT16(w) + HWEIGHT16((w) >> 16))
+#define HWEIGHT64(w) (HWEIGHT32(w) + HWEIGHT32((w) >> 32))
+
+/*
+ * Type invariant version that simply casts things to the
+ * largest type.
+ */
+#define HWEIGHT(w)   HWEIGHT64((u64)(w))
 
 /**
  * rol32 - rotate a 32-bit value left