buf_set_buf around 30% speed increase

buf_set_buf around 30% speed increase

Also i have checked the input of this function and in many cases
a simple byte copy is possible.

I have added this check now and is it possible the buffer is
copied byte by byte and not bit by bit.

With byte boundary input the test looks like this:

buf_set_buf 0x02000000 iteration test:
runtime (seconds): old: 6.828559 new: 0.436191 diff: 6.392368
runtime (seconds): old: 6.853636 new: 0.430389 diff: 6.423247
runtime (seconds): old: 6.794985 new: 0.423065 diff: 6.371920

Without:

buf_set_buf 0x02000000 iteration test:
runtime (seconds): old: 6.370869 new: 5.552624 diff: 0.818245
runtime (seconds): old: 6.420730 new: 5.665887 diff: 0.754843
runtime (seconds): old: 6.583306 new: 5.599021 diff: 0.984285

Regards,

Mathias