Remove comparison of unsigned expression < 0 warning

[wrongtest-intellif]

remove "comparison of unsigned expression < 0" warning

[tqchen]

Thanks @wrongtest . This might revealed another problem, as the default data structure for ndim should be int32_t as in https://github.com/dmlc/dlpack/blob/master/include/dlpack/dlpack.h#L136 So perhaps we want to change the API to use the new value.

There is always a temptation to use unsigned integers to represent values that can are non-negative. And there can be an active debate. On one hand, having unsigned values are great because we don't need to worry about negative checks like this one. On the other hand, unsigned values also creates potential problems, when there are a lot of implicit conversion between unsigned and signed, and potential underflow during subtraction.

So gradually my view has changed from use unsigned for non-neg values to use signed when possible. To make things consistent, perhaps we should change the arguments of these APIs to int or int32_t.

cc @liangfu @areusch

[areusch]

i guess the root problem here is we aren't able to use a higher-level language construct to describe the memory layout since we are serializing/deserializing. because of that, we're casting and can't rely on -Werror (my view is that most of these should be caught using -Werror) to really catch an underlying data format discrepancy; though, it should catch this bug. it looks like we aren't using -Werror with apps/bundle_deploy in master right now, we should probably turn that on and clean up all the warnings in a future PR.

[areusch]

@wrongtest I think it would make more sense here to change the type of ndim to int to match the dlpack.h header:
https://github.com/dmlc/dlpack/blob/master/include/dlpack/dlpack.h#L136

then we'd need to keep the original check. would you be up for making this change?

[wrongtest-intellif]

Sorry for not have noticed your comment later. I update related types of ndarray.c to int32_t. While original dlpack ndim is just defined as int, line 71 use also int instead of int32_t.

I run a local compile with -Wsign-compare -Wsign-conversion to ensure no inconsistency introduced internally in this file.

[tqchen]

Thanks @wrongtest @areusch !