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< Erlang ~ Efficient C binding (no sockets!) |
| senseiwa |
 Posted: Tue Jul 08, 2008 1:35 pm |
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Joined: 08 Jul 2008
Posts: 2
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Hi everyone!
I have a question that has been answered in the Erlang book, unfortunately that solution isn't satisfying.
My test bed is as follows: some ISO C libraries containing functions that should be called from an erlang program. All C functions will need several IEEE floating points, and clearly, using a socket-based approach as described in the book isn't the best option: it isn't fast, and it raises portability issues that I'd like to avoid.
What would you suggest to get the job done?
I am new to erlang, I program mainly in C and assembly, so you can understand my point of view 
Another (maybe) stupid question. The "erlang:binary_to_float(Binary)" and its counterpart are marked as internal. So what is the portable, erlang-proof way of passing IEEE floating point values to and from an erlang program?
Thanks to anyone giving hints! |
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| flodis |
| Posted: Wed Jul 09, 2008 8:28 am |
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Joined: 09 Jul 2008
Posts: 27
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I think you want to make a c driver. It allows you to call c functions directly from erlang processes.
I think binary_to_term/term_to_binary are the functions you are looking for. |
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| francesco |
| Posted: Wed Jul 09, 2008 9:19 am |
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Joined: 07 Jul 2006
Posts: 249
Location: London
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When interfacing to C, also take a look at erl_interface. It might be easier to use that writing your own drivers.
Francesco
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http://www.erlang-consulting.com |
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| martin |
| Posted: Wed Jul 09, 2008 11:19 am |
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Joined: 06 Aug 2006
Posts: 11
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Well what you want to look at are the example drivers in the otp_src_R12B-1/erts/example dir (also described in the ERTS user guide), further points worth mentioning is:
When writing drivers i find the control (see erl_ddll and driver_entry man pages) function easiest to use returning a binary constructed by the ei_x_encode_X API.
Further, do not hesitate to open ports to the driver as needed.
Use the try_load/3 try_unlaod/2 functions on demand since they are ref counted.
The threading model is to me unsound or its something i simply don't get so i simply avoid it and build a sep thread pool if needed...
Hope that helps
//Martin |
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| martin |
| Posted: Wed Jul 09, 2008 11:23 am |
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Joined: 06 Aug 2006
Posts: 11
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Some things i missed....
the binary returned should be constructed using the driver_alloc_binary and copied from the er_x_buff struct.
When opening the port pass the binary flag and or use the
set_port_control_flags(port, PORT_CONTROL_FLAG_BINARY); in the start function of your driver, then use the binary_to_term on the return value and term_to_binary on the input. |
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