copy-bit macro

[Colin Plumb]

I notice that a lot of code contains long lines of

if (input & INPUT_FLAG_FOO)
	output |= OUTPUT_FLAG_FOO;
if (input & INPUT_FLAG_BAR)
	output |= OUTPUT_FLAG_BAR
if (input & INPUT_FLAG_BAZ)
	output |= OUTPUT_FLAG_BAZ
etc.

The GCC output from this on the x86 is full of (slow) jumps.
Also, jumps inhibit optimization.
More efficient code, which can also be optimized around more,
is produced by

	output |= ((input / INPUT_FLAG_FOO) & 1) * OUTPUT_FLAG_FOO;
	output |= ((input / INPUT_FLAG_BAR) & 1) * OUTPUT_FLAG_BAR;
	output |= ((input / INPUT_FLAG_BAZ) & 1) * OUTPUT_FLAG_BAZ;

Withot having to define bit-shift amounts, GCC nicely optimizes that
into, e.g. 
	movl %edx,%eax
	sall $17,%eax
	andl $16777216,%eax
	orl %eax,%ecx

Might such a copy_bit macro be a useful general kernel utility?
I know Linus hates slow code, and a jump is slower than just about
anything.
--
	-Colin