[Blackclaws]

Big-endian data was refused outright — "Byte order conversion is not (yet) support by PureHDF" — which puts a large class of files out of reach. Big-endian is HDF5's portable choice and what a good deal of instrument software writes.

The refusal was incomplete, which mattered more than the refusal

It inspected only the top-level datatype, so anything nested went unguarded and was byte-copied through:

// dataset of compound { a: >i4, b: >f8 } holding (1, 2.0), (3, 4.0)
dataset.Read<Compound[]>()   →   (16777216, 3.16E-322), (50331648, 2.0553E-320)

No exception. The same held for an enumeration's base type, an array datatype's base type, and a variable-length sequence's base type. The honest refusal was the good case; everything it did not reach returned plausible-looking nonsense.

Byte order belongs to the leaf, not the dataset

A compound can hold one member of each order, so no single answer per read can be correct — mixed_compound in the fixture is exactly that, and would defeat any per-dataset approach.

Conversion is therefore driven by the datatype tree:

• the bulk decoders (a packed struct, an array datatype, a variable-length sequence) take a layout plan of (offset, width) pairs collected from the tree, and reverse those spans in the buffer the data was read into
• the element-at-a-time decoders convert per leaf, each member answering for its own order

Both routes are covered by tests, because a struct and a class decode by different paths and only one of them would otherwise be exercised.

The common path is untouched

Data already in the host's byte order gets the existing decoder exactly — the same static delegate, capturing nothing, with no extra pass over the buffer. The conversion is a second pass only where one is needed, and the read itself stays zero-copy either way.

Still refused

VAX floating-point, which is a different representation rather than a permutation of the bytes, and a variable-length datatype whose values would need conversion on the global heap, which this pass cannot reach. Both now fail with a message saying which.

Fixtures

AddEndianness writes through the C library with the file type as the memory type, so the bytes are exactly what a big-endian producer would emit rather than something converted on the way in. It covers a big-endian integer and float, a little-endian control, a wholly big-endian compound, a mixed-endianness compound, an enumeration over a big-endian base, and an array member over one.

🤖 Generated with Claude Code