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SubjectRe: [Linux-fbdev-devel] [PATCH 1/1 2.6.13] framebuffer: bit_putcs() optimization for 8x* fonts

>Probably you can make it even faster by avoiding the multiplication, like
>
> unsigned int offset = 0;
> for (i = 0; i < image.height; i++) {
> dst[offset] = src[i];
> offset += pitch;
> }
>

More than two decades ago I learned to avoid mul and imul. Use shifts,
add and lea instead,
that was the credo those days. The name of the game was CP/M 80/86, a86,
d86 and ddt ;-)

But let´s get serious again.

Your proposed change of the patch results in a 21 ms performance
decrease on my system.
Yes, I do know that this is hard to believe. I tested a similar
variation before, and the results
were even worse.

Avoiding mul is a good idea in assembly language today, but often it is
better to write a
multiplication with the loop counter in C and not to introduce an extra
variable instead. The
compiler will optimize the code and it´s easier for gcc without that
extra variable.

More interesting would be the question what should be done for idx==2 or
idx==3. Probably
fb_pad_aligned_buffer() is also slower for those cases. But does anybody
use such fonts?

cu,
knut
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