Collecting entropy from device_attach() times.

[Dag-Erling Smørgrav]

Pawel Jakub Dawidek <pjd at FreeBSD.org> writes:
> http://people.freebsd.org/~pjd/patches/harvest_device_attach.2.patch

You can replace highbit(x) - 9 with flsll(x) - 10.  Unfortunately, we
don't have flsll() in the kernel, but here's a simple implementation:

/*
 * Find last bit set in an unsigned long long.  Assumes that ULL is
 * always 64 bits wide while UL may be either 32 or 64 bits wide.
 */
static __inline unsigned int
flsll(unsigned long long mask)
{
#ifdef __LP64__
        return (flsl(mask));
#else
        return (mask >> 32 ? 32 + flsl(mask >> 32) : flsl(mask));
#endif
}

On i386 and amd64, flsl() is an inline function that expands to a single
assembler instruction.  On all other platforms, it is a function in
libkern, which is stupid - gcc and clang have builtin functions for it
which are almost certainly faster than a function call.

Same goes for s/last bit/first bit/; s/fls/ffs/g.

DES
-- 
Dag-Erling Smørgrav - des at des.no