Floating point and mipmapping and filtering
Some GPUs support floating point textures but don't support mipmapping or filtering.
How to detect if a GPU supports mipmapping and filtering?
If you want simplier approach then for FP16 textures check for GL_NV_fragment_program_3 - on NVIDIA this extension is suported since GeForce 6 and this GPU can filter/blend FP16 textures.
On ATI you need to check for GL_ATI_shader_texture_lod. That's FP16 blending. As for filtering it wasn't supported on Radeon X1k and below. X2k should support it - check for geometry shaders or some other SM4.0 feature.
<This information comes from <a href="http://www.opengl.org/discussion_boards/ubb/ultimatebb.php?ubb=get_topic;f=3;t=015278">http://www.opengl.org/discussion_boards/ubb/ultimatebb.php?ubb=get_topic;f=3;t=015278</a>