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[docs] qCompress/qUncompress: document size limits

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Zlib uses ulong in the interface, which, at least on Windows, is a
32-bit type, so qCompress cannot consume input and qUncompress cannot
produce output greater than ULONG_MAX, even on 64-bit platforms.

Document this limitation.

Pick-to: 6.4 6.3 6.2
Task-number: QTBUG-104972
Change-Id: I56c926a67f8705ef773977a86e157e6eb26aa585
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Marc Mutz 2022-09-06 22:02:47 +02:00
parent c97bcaaa1a
commit 6bdde52957
1 changed files with 22 additions and 0 deletions
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22
src/corelib/text/qbytearray.cpp
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@ -505,6 +505,15 @@ quint16 qChecksum(QByteArrayView data, Qt::ChecksumType standard)
The default value is -1, which specifies zlib's default
compression.
//![compress-limit-note]
\note The maximum size of data that this function can consume is limited by
what the platform's \c{unsigned long} can represent (a Zlib limitation).
That means that data > 4GiB can be compressed and decompressed on a 64-bit
Unix system, but not on a 64-bit Windows system. Portable code should
therefore avoid using qCompress()/qUncompress() to compress more than 4GiB
of input.
//![compress-limit-note]
\sa qUncompress(const QByteArray &data)
*/
@ -514,6 +523,8 @@ quint16 qChecksum(QByteArrayView data, Qt::ChecksumType standard)
Compresses the first \a nbytes of \a data at compression level
\a compressionLevel and returns the compressed data in a new byte array.
\include qbytearray.cpp compress-limit-note
*/
#ifndef QT_NO_COMPRESS
@ -578,6 +589,15 @@ QByteArray qCompress(const uchar* data, qsizetype nbytes, int compressionLevel)
contain the expected length (in bytes) of the uncompressed data,
expressed as an unsigned, big-endian, 32-bit integer.
//![uncompress-limit-note]
\note The maximum size of data that this function can produce is limited by
what the platform's \c{unsigned long} can represent (a Zlib limitation).
That means that data > 4GiB can be compressed and decompressed on a 64-bit
Unix system, but not on a 64-bit Windows system. Portable code should
therefore avoid using qCompress()/qUncompress() to compress more than 4GiB
of input.
//![uncompress-limit-note]
\sa qCompress()
*/
@ -594,6 +614,8 @@ static QByteArray invalidCompressedData()
Uncompresses the first \a nbytes of \a data and returns a new byte
array with the uncompressed data.
\include qbytearray.cpp uncompress-limit-note
*/
QByteArray qUncompress(const uchar* data, qsizetype nbytes)
{