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Hi Ed, Bitfields are a black sheep in the datatype family and aren't terribly well documented (which we're trying to work on). Say something if you think we've got a terrible gap about them somewhere. > Is there an example somewhere about using bitfields in HDF5? Hmm, you can look in the test/dtypes.c for some examples of using them. Search for "H5T_STD_B"... > Or can you just tell me what functions would be used to create a > bitfield? The H5Tset_precision() routine determines the number of bits in a datatype that are significant within it. > Limits on number of bits? Up to the size of the datatype that contains it (which is defined for up to 64-bit datatypes currently). > How are these stored then? Any sort of padding or what? We currently don't pack them, so a 13-bit field in a 32-bit datatype still takes up 4 bytes of space. Frankly, I think this is a bit of a bug, but it's a fairly complicated problem to pack the bits on disk (in light of using bitfields in compound, array and variable-length datatypes mostly) and noone has whined strongly about it, so its been the status quo for a while now. :-/ Quincey