Re: [vsipl++] [patch] Fix for generic pwarp

[Jules Bergmann <jules@xxxxxxxxxxxxxxxx>]

Stefan Seefeld wrote:
> Jules Bergmann wrote:
> > Stefan,
> >
> > This patch attempts to fix the generic pwarp impl so that it doesn't
> > access memory past the end of the input image.
> >
> > Can you give a spin on windows to see if it fixes the segfault?
> Unfortunately it still fails.
> Luckily, though, I have been able to reproduce the failure under Linux,
> using ElectricFence, and it seems to be the exact same place as on
> Windows, at least if I trust the debugger(s):
Can you try running the patch through electric fence?

In particular, it replaces

> z11 = *(p + in_stride_0 + 1)
with

> +	T z11 = *(p + off_11); // in.get(v0+1, u0+1);
where

> +	stride_type off_11 = std::min<stride_type>(in_stride_0 + 1, limit);
i.e. the patch attempts to clip off_11 if it results in an address 
beyond the image.  Perhaps I am setting limit incorrectly.

The problem with adjusting the clipping

-      if (u >= 0 && u <= u_clip && v >= 0 && v <= v_clip)
+      if (u >= 0 && u < u_clip && v >= 0 && v < v_clip)

is that u == u_clip is actually valid, since it falls exactly on a pixel 
and does not require interpolation with u_clip+1.  (This is the case 
mentioned yesterday, where values outside the image may be read, but are 
not used in computing the result (since they are weighted with 0)).
				-- Jules

--
Jules Bergmann
CodeSourcery
jules@xxxxxxxxxxxxxxxx
(650) 331-3385 x705