Re: Image scaling performance

["Vladimir 'φ-coder/phcoder' Serbinenko" <phcoder@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 2390 bytes --]

On 25.02.2015 19:46, Michael Zimmermann wrote:
> oh ok so linux's div/mod/... assembler is as slow/fast as grub's code?
> Linux uses armv5>= ifdefs. Maybe we could optimized things a little :)
> About scale_nn,
> amarullz(https://plus.google.com/u/0/+AhmadAmarullah/about) wrote a
> optimized version without divs:
> loops: http://pastebin.com/MaZqWSA9
> memcpy: http://pastebin.com/iNq0V5Tw
>
Please try my patch (reattached here after minor fixes). The patch by 
anonymous source, sent by third-party through pastebin isn't acceptable 
from legal perspective
> this code works a little faster. I'm still questioning the efficiency
> math operations because on slow devices there are other bottlenecks of
> the same kind(like de/compression).
>
> On Wed, Feb 25, 2015 at 7:41 PM, Vladimir 'phcoder' Serbinenko
> <phcoder@gmail.com> wrote:
>> ARMv7 doesn't mandate div instructions. It's a separate flag in features.
>> GRUB supports earlier CPUs as well and we use them for testing. My only test
>> machine is armv6
>>
>> Le 2015-02-25 19:38, "Michael Zimmermann" <sigmaepsilon92@gmail.com> a écrit
>> :
>>
>>> Why u think the native div code would crash on most devices? I support
>>> ARMv7+ only anyway.
>>>
>>> On Wed, Feb 25, 2015 at 5:23 PM, Leif Lindholm <leif.lindholm@linaro.org>
>>> wrote:
>>>> On Wed, Feb 25, 2015 at 03:45:40PM +0000, Leif Lindholm wrote:
>>>>>>>> Some technical info:
>>>>>>>> ARMv7
>>>>>>>> Linaro GCC 4.9
>>>>>
>>>>> I don't see any calls to any of the __aeabi helpers generated for this
>>>>> file with current head. Which specific Linaro toolchain are you using?
>>>>> (mine is"Linaro GCC 4.9-2014.09").
>>>>
>>>> Scratch that, I do see them. Just failing to drive the tools properly.
>>>>
>>>> /
>>>>      Leif
>>>>
>>>> _______________________________________________
>>>> Grub-devel mailing list
>>>> Grub-devel@gnu.org
>>>> https://lists.gnu.org/mailman/listinfo/grub-devel
>>>
>>> _______________________________________________
>>> Grub-devel mailing list
>>> Grub-devel@gnu.org
>>> https://lists.gnu.org/mailman/listinfo/grub-devel
>>
>>
>> _______________________________________________
>> Grub-devel mailing list
>> Grub-devel@gnu.org
>> https://lists.gnu.org/mailman/listinfo/grub-devel
>>
>
> _______________________________________________
> Grub-devel mailing list
> Grub-devel@gnu.org
> https://lists.gnu.org/mailman/listinfo/grub-devel
>


[-- Attachment #2: scale.diff --]
[-- Type: text/x-diff, Size: 1442 bytes --]

diff --git a/grub-core/video/bitmap_scale.c b/grub-core/video/bitmap_scale.c
index 0b93d02..64bacbf 100644
--- a/grub-core/video/bitmap_scale.c
+++ b/grub-core/video/bitmap_scale.c
@@ -366,22 +366,31 @@ scale_nn (struct grub_video_bitmap *dst, struct grub_video_bitmap *src)
   /* bytes_per_pixel is the same for both src and dst. */
   unsigned bytes_per_pixel = dst->mode_info.bytes_per_pixel;
 
-  unsigned dy;
-  for (dy = 0; dy < dh; dy++)
+  unsigned dy, sy, ystep, yfrac, yover;
+  unsigned dx, sx, xstep, xfrac, xover;
+  ystep = sw / dw;
+  yover = sw % dw;
+  xstep = sh / dh;
+  xover = sh % dh;
+
+  for (dy = 0, sy = 0, yfrac = 0; dy < dh; dy++, sy += ystep, yfrac += yover)
     {
-      unsigned dx;
-      for (dx = 0; dx < dw; dx++)
+      if (yfrac > dw)
+	{
+	  yfrac -= dw;
+	  sy++;
+	}
+      for (dx = 0, sx = 0, xfrac = 0; dx < dw; dx++, sx += xstep, xfrac += xover)
         {
           grub_uint8_t *dptr;
           grub_uint8_t *sptr;
-          unsigned sx;
-          unsigned sy;
           unsigned comp;
 
-          /* Compute the source coordinate that the destination coordinate
-             maps to.  Note: sx/sw = dx/dw  =>  sx = sw*dx/dw. */
-          sx = sw * dx / dw;
-          sy = sh * dy / dh;
+	  if (xfrac > dh)
+	    {
+	      xfrac -= dh;
+	      sx++;
+	    }
 
           /* Get the address of the pixels in src and dst. */
           dptr = ddata + dy * dstride + dx * bytes_per_pixel;