The IBM-provided zlib compatible C library provides the following query functions in addition to the standard zlib functions:

deflateHwAvail(buflen)

Determines if the compression accelerator is available for a deflate operation. The input parameter buflen is an integer that represents the input buffer size of the first deflate request. The function returns an integer with a value of 1 if the compression accelerator will be used for the deflate operation or a value of 0 if software will be used instead.

inflateHwAvail(buflen)

Determines if the compression accelerator is available for an inflate operation. The input parameter buflen is an integer that represents the input buffer size of the first inflate request. The function returns an integer with a value of 1 if the compression accelerator will be used for this inflate operation or a value of 0 if software will be used instead.

hwCheck(strm)

Determines if a zlib stream is using the compression accelerator or software compression. The input parameter strm is a pointer to a zlib z_stream structure to check. The function returns an integer with a value of 0 if the stream has gone to the compression accelerator, a value of 1 if the stream is pending to go to the compression accelerator, but still could fall back to software compression, a value of 2 if the stream has gone to software compression, or Z_STREAM_ERROR if the stream has not been initialized correctly.