b2nd format is specified as a metalayer on top of a Blosc2 container for storing multidimensional information. Specifically, this metalayer is named 'b2nd' and follows this format:
|-0-|-1-|-2-|-3-|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~| | 9X| v | nd| 9X| shape | 9X| chunkshape | 9X| blockshape | |---|---|---|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~|---|~~~~~~~~~~~~~~~~| ^ ^ ^ ^ ^ ^ | | | | | | | | | | | +--[msgpack] fixarray with X=nd elements | | | | +--[msgpack] fixarray with X=nd elements | | | +--[msgpack] fixarray with X=nd elements | | +--[msgpack] positive fixnum for the number of dimensions (up to 127) | +--[msgpack] positive fixnum for the metalayer format version (up to 127) +---[msgpack] fixarray with X=7 elements
The shape section is meant to store the actual shape info:
|---|--8 bytes---|---|--8 bytes---|~~~~~|---|--8 bytes---| | d3| first_dim | d3| second_dim | ... | d3| nth_dim | |---|------------|---|------------|~~~~~|---|------------| ^ ^ ^ | | | | | +--[msgpack] int64 | +--[msgpack] int64 +--[msgpack] int64
Next, the chunkshape section is meant to store the actual chunk shape info:
|---|--4 bytes---|---|--4 bytes---|~~~~~|---|--4 bytes---| | d2| first_dim | d2| second_dim | ... | d2| nth_dim | |---|------------|---|------------|~~~~~|---|------------| ^ ^ ^ | | | | | +--[msgpack] int32 | +--[msgpack] int32 +--[msgpack] int32
Next, the blockshape section is meant to store the actual block shape info:
|---|--4 bytes---|---|--4 bytes---|~~~~~|---|--4 bytes---| | d2| first_dim | d2| second_dim | ... | d2| nth_dim | |---|------------|---|------------|~~~~~|---|------------| ^ ^ ^ | | | | | +--[msgpack] int32 | +--[msgpack] int32 +--[msgpack] int32
Finally, the dtype section is meant to store the data type information:
|---|---|--4 bytes---|--------------| | XX| db| dtype_len | dtype_string | |---|---|------------|--------------| ^ ^ | | | +--[msgpack] str32 +--[msgpack] positive fixint (7-bit integer). dtype_format; 0 means NumPy format.
The 0 value for dtype_format means that the dtype_string field follows the NumPy convention (e.g. an int32_t dtype is represented as "<i4"). For more examples on NumPy dtype specs, see https://numpy.org/doc/stable/reference/arrays.dtypes.html#arrays-dtypes-constructing.