DM: find max component difference

DM: find max component difference

So far unused except to back BitmapsEqual, but I want to play with it in CLs I'm working on.

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=14759

[reed1, 2014-05-16 12:29:59]

lgtm

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.cpp
File dm/DMUtil.cpp (right):

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.cpp#newcode87
dm/DMUtil.cpp:87: return a.info() == b.info() && 0 == MaxComponentDifference(a,
b);
This seems like it will be slower than just memcmp for straight equals
calculation...

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.h
File dm/DMUtil.h (right):

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.h#newcode32
dm/DMUtil.h:32: unsigned MaxComponentDifference(const SkBitmap& a, const
SkBitmap& b);
For the future, it might prove useful to return 4 values, one for each
component, as that may be interesting to the operator. Not for this CL per-se.

[mtklein, 2014-05-16 13:00:53]

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.cpp
File dm/DMUtil.cpp (right):

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.cpp#newcode87
dm/DMUtil.cpp:87: return a.info() == b.info() && 0 == MaxComponentDifference(a,
b);
On 2014/05/16 12:30:00, reed1 wrote:
> This seems like it will be slower than just memcmp for straight equals
> calculation...

Definitely, but it's low enough down the profile I haven't noticed the extra
cost yet.  I sort of also want to provoke myself into accelerating the component
comparison.

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.h
File dm/DMUtil.h (right):

https://codereview.chromium.org/290043005/diff/20001/dm/DMUtil.h#newcode32
dm/DMUtil.h:32: unsigned MaxComponentDifference(const SkBitmap& a, const
SkBitmap& b);
On 2014/05/16 12:30:00, reed1 wrote:
> For the future, it might prove useful to return 4 values, one for each
> component, as that may be interesting to the operator. Not for this CL per-se.

Agreed.

[mtklein, 2014-05-16 13:01:03]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2014-05-16 13:01:14]

CQ is trying da patch. Follow status at
 https://skia-tree-status.appspot.com/cq/mtklein@chromium.org/290043005/20001

[commit-bot: I haz the power, 2014-05-16 13:03:47]

Change committed as 14759