64 bit of data per pixel on 965GM?

I'd like to try GPGPU on my 965GM. However each computation would output
a 64 bit integer value. How can I do this?
glxinfo tells me about RGBA8888 visuals only, that could be used as 32
bit integer per pixel. What could I do to get 64 bit?
The visuals that have a 64 bit accum buffer are markes as slow, which
means software rendering I suppose.

Philipp

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