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Incorrect address for unsigned integers with ffi #1315

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djberg96 opened this issue Dec 7, 2013 · 7 comments
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Incorrect address for unsigned integers with ffi #1315

djberg96 opened this issue Dec 7, 2013 · 7 comments
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@djberg96
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djberg96 commented Dec 7, 2013

It seems that when using JRuby and ffi it returns an incorrect value for the address of an unsigned integer:

# Should be (1 << FFI::Platform::ADDRESS_SIZE) - 1
FFI::Pointer.new(-1).address # Returns -1 instead of correct value

This came up when trying to define INVALID_HANDLE_VALUE on Windows which internally is defined using a cast:

// 0xFFFFFFFF on 32 bit systems, 0xFFFFFFFFFFFFFFFF on 64 bit systems
INVALID_HANDLE_VALUE = (DWORD)-1;

I realize JRuby isn't big on addresses in general, but here I think we can simulate casting a negative int here to match C's behavior.

Originally reported on the ffi project, but was told to report it here.
@larskanis
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For reference the issue on ffi gem: ffi/ffi#313

@tduehr
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tduehr commented Feb 5, 2015

This is solved by:

address && Platform.getPlatform().addressMask()

The only question is where do we perform that? at initialization? on #address? both?
@enebo @headius comments?

@djberg96
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djberg96 commented Feb 5, 2016

Still happening as of 9.0.5.0.

@tduehr
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tduehr commented Feb 5, 2016

I'm not sure this can be fixed on 64bit systems. Since Java doesn't have unsigned integer types, I think we'd have to change the API to return a BigInteger to get 0xFFFFFFFFFFFFFFFF as a positive value.

@djberg96
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@tduehr Any update?

@djberg96
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@enebo @headius @tduehr Still happening as of 9.1.12.

@djberg96
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Looks like it's dead, just cleaning up my queue.

@enebo enebo added this to the Invalid or Duplicate milestone Apr 19, 2018
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@enebo @tduehr @djberg96 @larskanis