Function blosc_sys::blosc_compress

pub unsafe extern "C" fn blosc_compress(
    clevel: c_int, 
    doshuffle: c_int, 
    typesize: usize, 
    nbytes: usize, 
    src: *const c_void, 
    dest: *mut c_void, 
    destsize: usize
) -> c_int

Compress a block of data in the src buffer and returns the size of the compressed block. The size of src buffer is specified by nbytes. There is not a minimum for src buffer size (nbytes).

clevel is the desired compression level and must be a number between 0 (no compression) and 9 (maximum compression).

doshuffle specifies whether the shuffle compression filters should be applied or not. BLOSC_NOSHUFFLE means not applying it, BLOSC_SHUFFLE means applying it at a byte level and BLOSC_BITSHUFFLE at a bit level (slower but may achieve better entropy alignment).

typesize is the number of bytes for the atomic type in binary src buffer. This is mainly useful for the shuffle filters. For implementation reasons, only a 1 < typesize < 256 will allow the shuffle filter to work. When typesize is not in this range, shuffle will be silently disabled.

The dest buffer must have at least the size of destsize. Blosc guarantees that if you set destsize to, at least, (nbytes + BLOSC_MAX_OVERHEAD), the compression will always succeed. The src buffer and the dest buffer can not overlap.

Compression is memory safe and guaranteed not to write the dest buffer beyond what is specified in destsize.

If src buffer cannot be compressed into destsize, the return value is zero and you should discard the contents of the dest buffer.

A negative return value means that an internal error happened. This should never happen. If you see this, please report it back together with the buffer data causing this and compression settings.

Environment variables

blosc_compress() honors different environment variables to control internal parameters without the need of doing that programatically. Here are the ones supported:

BLOSC_CLEVEL=(INTEGER): This will overwrite the clevel parameter before the compression process starts.

BLOSC_SHUFFLE=[NOSHUFFLE | SHUFFLE | BITSHUFFLE]: This will overwrite the doshuffle parameter before the compression process starts.

BLOSC_TYPESIZE=(INTEGER): This will overwrite the typesize parameter before the compression process starts.

BLOSC_COMPRESSOR=[BLOSCLZ | LZ4 | LZ4HC | SNAPPY | ZLIB]: This will call blosc_set_compressor(BLOSC_COMPRESSOR) before the compression process starts.

BLOSC_NTHREADS=(INTEGER): This will call blosc_set_nthreads(BLOSC_NTHREADS) before the compression process starts.

BLOSC_BLOCKSIZE=(INTEGER): This will call blosc_set_blocksize(BLOSC_BLOCKSIZE) before the compression process starts. NOTE: The blocksize is a critical parameter with important restrictions in the allowed values, so use this with care.

BLOSC_NOLOCK=(ANY VALUE): This will call blosc_compress_ctx() under the hood, with the compressor, blocksize and numinternalthreads parameters set to the same as the last calls to blosc_set_compressor(), blosc_set_blocksize() and blosc_set_nthreads(). BLOSC_CLEVEL, BLOSC_SHUFFLE, BLOSC_TYPESIZE environment vars will also be honored.

BLOSC_SPLITMODE=[ FORWARD_COMPAT | AUTO | ALWAYS | NEVER ]: This will call blosc_set_splitmode() with the different supported values. See blosc_set_splitmode() docstrings for more info on each mode.