[PATCH 9/12] generic hweight64()

This patch introduces the C-language equivalent of the function:
unsigned long hweight64(__u64 w);

HAVE_ARCH_HWEIGHT64_BITOPS is defined when the architecture has its own
version of these functions.

This code largely copied from:
include/linux/bitops.h

Index: 2.6-git/include/asm-generic/bitops.h
===================================================================
--- 2.6-git.orig/include/asm-generic/bitops.h	2006-01-25 19:14:11.000000000 +0900
+++ 2.6-git/include/asm-generic/bitops.h	2006-01-25 19:14:11.000000000 +0900
@@ -491,6 +491,25 @@
 
 #endif /* HAVE_ARCH_HWEIGHT_BITOPS */
 
+#ifndef HAVE_ARCH_HWEIGHT64_BITOPS
+
+static inline unsigned long hweight64(__u64 w)
+{
+#if BITS_PER_LONG < 64
+	return hweight32((unsigned int)(w >> 32)) + hweight32((unsigned int)w);
+#else
+	u64 res;
+	res = (w & 0x5555555555555555ul) + ((w >> 1) & 0x5555555555555555ul);
+	res = (res & 0x3333333333333333ul) + ((res >> 2) & 0x3333333333333333ul);
+	res = (res & 0x0F0F0F0F0F0F0F0Ful) + ((res >> 4) & 0x0F0F0F0F0F0F0F0Ful);
+	res = (res & 0x00FF00FF00FF00FFul) + ((res >> 8) & 0x00FF00FF00FF00FFul);
+	res = (res & 0x0000FFFF0000FFFFul) + ((res >> 16) & 0x0000FFFF0000FFFFul);
+	return (res & 0x00000000FFFFFFFFul) + ((res >> 32) & 0x00000000FFFFFFFFul);
+#endif
+}
+
+#endif /* HAVE_ARCH_HWEIGHT64_BITOPS */
+
 #endif /* __KERNEL__ */
 
 #endif /* _ASM_GENERIC_BITOPS_H */
-
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