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

On Tue, 30 Aug 2005, Knut Petersen wrote:

> > 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.

Could you try the patch below, for a few extra cycles you might want to
make it an inline function.

bye, Roman

Index: linux-2.6/drivers/video/fbmem.c
===================================================================
--- linux-2.6.orig/drivers/video/fbmem.c 2005-08-30 01:55:18.000000000 +0200
+++ linux-2.6/drivers/video/fbmem.c 2005-08-30 21:10:25.705462837 +0200
@@ -82,11 +82,11 @@ void fb_pad_aligned_buffer(u8 *dst, u32
{
int i, j;

+ d_pitch -= s_pitch;
for (i = height; i--; ) {
/* s_pitch is a few bytes at the most, memcpy is suboptimal */
for (j = 0; j < s_pitch; j++)
- dst[j] = src[j];
- src += s_pitch;
+ *dst++ = *src++;
dst += d_pitch;
}
}
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