Fix issue #337 and #457

[ryanrhymes]

This PR changes number type from int32 to int64 in underlying indexing and slicing function. This change affects many c code in owl core, therefore needs careful examination before merge.

[jzstark]

I've tried the new branch and do make test. All tests pass except for the know "sylvester" test.

I then tried the DNNs, including mnist training example, the inception inference, and fast style transfer, and the computation results seem normal.

The only issue I get is that there are several compilation warnings:

dune build @install
      ocamlc src/owl/owl_ndarray_transpose_stub.o
In file included from src/owl/core/owl_ndarray_transpose_stub.c:17:
src/owl/core/owl_ndarray_transpose_impl.h:241:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = X->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_ndarray_transpose_stub.c:26:
src/owl/core/owl_ndarray_transpose_impl.h:241:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = X->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_ndarray_transpose_stub.c:35:
src/owl/core/owl_ndarray_transpose_impl.h:241:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = X->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_ndarray_transpose_stub.c:44:
src/owl/core/owl_ndarray_transpose_impl.h:241:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = X->dim;
        ^ ~~~~~~
4 warnings generated.
      ocamlc src/owl/owl_slicing_fancy_stub.o
In file included from src/owl/core/owl_slicing_fancy_stub.c:19:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:28:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:37:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:46:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:57:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:66:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:75:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_fancy_stub.c:84:
src/owl/core/owl_slicing_fancy_impl.h:92:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  fp->n = Y->dim;
        ^ ~~~~~~
8 warnings generated.
      ocamlc src/owl/owl_slicing_basic_stub.o
In file included from src/owl/core/owl_slicing_basic_stub.c:20:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:29:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:38:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:47:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:58:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:67:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:76:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
In file included from src/owl/core/owl_slicing_basic_stub.c:85:
src/owl/core/owl_slicing_basic_impl.h:239:9: warning: incompatible pointer types assigning to 'int64_t *' (aka 'long long *') from 'intnat []' [-Wincompatible-pointer-types]
  sp->n = Y->dim;
        ^ ~~~~~~
8 warnings generated.

[mseri]

Maybe we should use intnat as well. It is defined by the ocaml runtime and chooses between int and long int depending on the arch support: https://github.com/ocaml/ocaml/blob/fe31a0179dd0575f217dcde11ca4dabcc2673c57/runtime/caml/config.h#L127

It is used pervasively in the mmap code in ocaml and would prevent breakage in 32bit arch.

What do you think?

[jzstark]

But perhaps sticking with one explicit type would potentially reduce bug? I'm thinking how widely is Owl used on 32bit machines.