intel/isa-l

Control over `BFINAL` bit

Closed this issue · 2 comments

zbjornson commented

Hi,

I'm trying to concatenate raw DEFLATE blocks produced by isal_deflate_stateless(). ISA-L appears to always set the BFINAL bit on the last block of the output though. It also appears that it can produce multiple blocks, so it's not safe to just clear the first bit of the first byte.

The header says FULL_FLUSH will byte align the output deflate block so additional blocks can be easily appended, so I'm hoping this scenario has been thought through before.

For comparison, I think zlib only sets BFINAL when Z_FINISH is used, and Z_FINISH must be used at least once per stream.

Thanks-

gbtucker commented

Have you seen how the igzip cli program uses isal_deflate_stateless() to independently generate deflate blocks and concatenate them? https://github.com/intel/isa-l/blob/master/programs/igzip_cli.c#L533 It uses full_flush.

zbjornson commented

Ohh, it looks like end_of_stream is what controls whether or not BFINAL is set. Thanks for the pointer.