How is af_array data arranged in memory?

[Alex Shroyer]

Hi, 

I'm trying to bind some ArrayFire functions with an interpreted language (which has a C FFI) and wondering how to get data in and out.

Currently I'm just focusing on getting data *out* of ArrayFire.

I'm using functions like af_create_handle and af_identity to generate data, but I do not know how to interpret the resulting pointers.

For example, if I want to transfer a 2x3 matrix of 64-bit ints back into my interpreted language, is there a specific function I should use to put the data into some kind of canonical form, or alternatively is there documentation about the array/struct layout so that I can deserialize it on the interpreter side?

Thanks,

Alex

[uma...@gmail.com]

You can use af_get_data_ptr to transfer data to host memory. The pointer returned will be in column major order.

So if your matrix looks like this:

1 2 3

4 5 6

The data pointer will return an array that will contain the following values:

1 4 2 5 3 6

Best,

Umar

[John Melonakos]

You can use af_get_data_ptr to transfer data to host memory. The pointer returned will be in column major order. 

So if your matrix looks like this:

1 2 3

4 5 6

The data pointer will return an array that will contain the following values:

1 4 2 5 3 6

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[Alex Shroyer]

Thanks for the tip!

I'm trying this (using python-like pseudocode)

1. p1 = host_allocate(num_bytes=16)

2. h1 = ffi(af_create_handle(p1,  ndims=2, dims=[4,4],  'f64'))

3. i1 = ffi(af_identity(h1, ndims=2, dims=[4,4], 'f64'))

4. result = ffi(af_get_data_ptr(p1, h1))

The problem I get with the above is that result is 0 (null pointer), so it appears that af_get_data_ptr did not succeed, even though AF_ERROR == AF_SUCCESS for all ffi calls.

What does it mean that af_get_data_ptr sets the destination pointer to 0?

[Alex Shroyer]

Oh, I found my error! 

I should have used af_get_data_ptr(p1, i1).

Thanks again,

Alex

[John Melonakos]

Wonderful, let us know if you have any other questions.

To view this discussion on the web visit https://groups.google.com/d/msgid/arrayfire-users/c2e9c6c6-2c03-4c70-afcf-4f7851a7a706n%40googlegroups.com.