fastest way to write a bitstream on modern x86 hardware

Question

What is the fastest way to write a bitstream on x86/x86-64? (codeword <= 32bit)

by writing a bitstream I refer to the process of concatenating variable bit-length

Answer 1

You'll probably have to wait until 2013 to get hold of real HW, but the "Haswell" new instructions will bring proper vectorised shifts (ie the ability to shift each vector element by different amounts specified in another vector) to x86/AVX. Not sure of details (plenty of time to figure them out), but that will surely enable a massive performance improvement in bitstream construction code.