Blosc Header Format
Blosc (as of Version 1.0.0) has the following 16 byte header that stores
information about the compressed buffer:
|-0-|-1-|-2-|-3-|-4-|-5-|-6-|-7-|-8-|-9-|-A-|-B-|-C-|-D-|-E-|-F-|
^ ^ ^ ^ | nbytes | blocksize | ctbytes |
| | | |
| | | +--typesize
| | +------flags
| +----------versionlz
+--------------version
Datatypes of the Header Entries
All entries are little endian.
| version: | (uint8) Blosc format version.
|
|---|
| versionlz: | (uint8) Version of the internal compressor used.
|
|---|
| flags and compressor enumeration: | (bitfield) The flags of the buffer
bit 0 (0x01): | Whether the byte-shuffle filter has been applied or not. |
|---|
bit 1 (0x02): | Whether the internal buffer is a pure memcpy or not. |
|---|
bit 2 (0x04): | Whether the bit-shuffle filter has been applied or not. |
|---|
bit 3 (0x08): | Reserved, must be zero. |
|---|
bit 4 (0x10): | If set, the blocks will not be split in sub-blocks during compression. |
|---|
bit 5 (0x20): | Part of the enumeration for compressors. |
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bit 6 (0x40): | Part of the enumeration for compressors. |
|---|
bit 7 (0x80): | Part of the enumeration for compressors. |
|---|
The last three bits form an enumeration that allows to use alternative
compressors.
0: | blosclz |
|---|
1: | lz4 or lz4hc |
|---|
2: | snappy |
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3: | zlib |
|---|
4: | zstd |
|---|
|
|---|
| typesize: | (uint8) Number of bytes for the atomic type.
|
|---|
| nbytes: | (uint32) Uncompressed size of the buffer.
|
|---|
| blocksize: | (uint32) Size of internal blocks.
|
|---|
| ctbytes: | (uint32) Compressed size of the buffer.
|
|---|