But thinking about it again that’s probably suboptimal but not fatal.
However these lines immediately before that if statement look like you
are accessing the input array x *before* checking bounds
neighbor_idx(0) = i-shift(1);
neighbor_idx(1) = j+shift(0);
int neighbor_val = x(neighbor_idx(0), neighbor_idx(1));
So this should fix, I think:
if((neighbor_idx(0) < nr) && (neighbor_idx(1) < nc) &&
(neighbor_idx(0) >= 0) && (neighbor_idx(1) >= 0)){
int neighbor_val = x(neighbor_idx(0), neighbor_idx(1));
GLCM(focal_val,neighbor_val) = GLCM(focal_val,neighbor_val)+1;
GLCM(neighbor_val,focal_val) = GLCM(neighbor_val,focal_val)+1;
}
Best,
Greg.
https://github.com/ailich/GLCMTextures/blob/2d69b5b71c558b89463e4726140d3378f5674fa6/src/glcm_cpp_functions.cpp#L47-L53
Sent from my iPhone
On 29 Oct 2020, at 06:57, Gregory Jefferis
<jeffe...@mrc-lmb.cam.ac.uk> wrote:
Alexander,
I think your bounds checking code uses bitwise & rather than logical
&&
if((neighbor_idx(0) < nr) & (neighbor_idx(1) < nc) &
(neighbor_idx(0) >= 0) & (neighbor_idx(1) >= 0)){
GLCM(focal_val,neighbor_val) = GLCM(focal_val,neighbor_val)+1;
GLCM(neighbor_val,focal_val) = GLCM(neighbor_val,focal_val)+1;
}
Best,
Greg.
Sent from my iPhone
On 29 Oct 2020, at 00:15, Dirk Eddelbuettel <e...@debian.org> wrote:
Alexander,
A segmentation fault can take the session down as it is undefined
behavior,
yet is almost always the error of the programmers.
We have written the basic accessors for efficiency so they do not
check. But
there are checking accessor that throw with a proper message:
R> Rcpp::cppFunction("void foo(IntegerVector x) { int n = x.size();
Rcpp::Rcout << x.at(n+1) << std::endl; }")
R> foo(1:3)
Error in foo(1:3) : Index out of bounds: [index=4; extent=3].
R>
No segfault, just a clean error message. RcppArmadillo has something
similar.
By contrast if you don't check you can get garbage or bad behavior:
R> Rcpp::cppFunction("void bar(IntegerVector x) { int n = x.size();
Rcpp::Rcout << x[n+1] << std::endl; }")
R> bar(1:3)
1358954573
R>
No crash but not exactly 'right' either.
The other thing you can do is to couple R with gdb to run under the
debugger
to get access to your indexing variables. There are some writeups in
different places as it takes two steps---but may be worth it. Here
are two
quick hits from StackOverflow:
https://stackoverflow.com/questions/21226337/what-are-productive-ways-to-debug-rcpp-compiled-code-loaded-in-r-on-os-x-maveri
https://stackoverflow.com/questions/11345537/debugging-line-by-line-of-rcpp-generated-dll-under-windows
Dirk
--
https://dirk.eddelbuettel.com | @eddelbuettel | e...@debian.org
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--
Gregory Jefferis, PhD Tel: +44 1223 267048
Division of Neurobiology
MRC Laboratory of Molecular Biology
Francis Crick Avenue
Cambridge Biomedical Campus
Cambridge, CB2 0QH, UK
http://www2.mrc-lmb.cam.ac.uk/group-leaders/h-to-m/g-jefferis
http://jefferislab.org
http://www.zoo.cam.ac.uk/research/groups/connectomics
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