93aa02e671
The zlib convenience API we've been using so far has two problems: - On Windows-64, where sizeof(long) == 4, the use of ulong for sizes meant that we could not compress data compressable on other 64-bit platforms (Unix). While zstream also uses ulong, being a stream API, it allows feeding data in chunks. The total_in and total_out members are only required for gzip compression and are otherwise just informational. They're unsigned, so their overflow does not cause UB. In summary, using zstream + deflate() allows us to compress more than 4GiB of data even on Windows-64. - On all platforms, we always allocated the output buffer in such a way as to accommodate the pathological case of random, incompressible data, so the output buffer was larger than the input. Using zstream + deflate(), we can start with a smaller buffer, then let zlib pick up where it left off when it ran out of output buffer space, saving memory in the common case that compression meaningfully reduces the size. To avoid the first few rounds of reallocations, we continue to use zlib's compressBound() for input less than 256KiB. This completely fixes the compression side of QTBUG-106542 and QTBUG-104972. Fixes: QTBUG-104972 Fixes: QTBUG-106542 Change-Id: Ia7e6c38403906b35462480fd611b482f05a5c59c Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org> Reviewed-by: Thiago Macieira <thiago.macieira@intel.com> Reviewed-by: Edward Welbourne <edward.welbourne@qt.io> (cherry picked from commit 2fd990b386c3555cf66cd3efff0d6a47cdc63763) Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>