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diff --git a/package/source/zipapi/ThreadedDeflater.cxx b/package/source/zipapi/ThreadedDeflater.cxx
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+++ b/package/source/zipapi/ThreadedDeflater.cxx
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+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * This file incorporates work covered by the following license notice:
+ *
+ *   Licensed to the Apache Software Foundation (ASF) under one or more
+ *   contributor license agreements. See the NOTICE file distributed
+ *   with this work for additional information regarding copyright
+ *   ownership. The ASF licenses this file to you under the Apache
+ *   License, Version 2.0 (the "License"); you may not use this file
+ *   except in compliance with the License. You may obtain a copy of
+ *   the License at http://www.apache.org/licenses/LICENSE-2.0 .
+ */
+
+#include <ThreadedDeflater.hxx>
+#include <zlib.h>
+#include <com/sun/star/packages/zip/ZipConstants.hpp>
+#include <sal/log.hxx>
+
+using namespace com::sun::star::packages::zip::ZipConstants;
+using namespace com::sun::star;
+
+namespace ZipUtils
+{
+const sal_Int64 MaxBlockSize = 128 * 1024;
+
+// Parallel ZLIB compression using threads. The class internally splits the data into
+// blocks and spawns ThreadPool tasks to process them independently. This is achieved
+// in a similar way how pigz works, see comments from Mark Adler at
+// https://stackoverflow.com/questions/30294766/how-to-use-multiple-threads-for-zlib-compression
+// and
+// https://stackoverflow.com/questions/30794053/how-to-use-multiple-threads-for-zlib-compression-same-input-source
+
+// Everything here should be either read-only, or writing to distinct data, or atomic.
+
+class ThreadedDeflater::Task : public comphelper::ThreadTask
+{
+    z_stream stream;
+    ThreadedDeflater* deflater;
+    int sequence;
+    int blockSize;
+    bool firstTask : 1;
+    bool lastTask : 1;
+
+public:
+    Task(ThreadedDeflater* deflater_, int sequence_, int blockSize_, bool firstTask_,
+         bool lastTask_)
+        : comphelper::ThreadTask(deflater_->threadTaskTag)
+        , stream()
+        , deflater(deflater_)
+        , sequence(sequence_)
+        , blockSize(blockSize_)
+        , firstTask(firstTask_)
+        , lastTask(lastTask_)
+    {
+    }
+
+private:
+    virtual void doWork() override;
+};
+
+ThreadedDeflater::ThreadedDeflater(sal_Int32 nSetLevel)
+    : threadTaskTag(comphelper::ThreadPool::createThreadTaskTag())
+    , totalIn(0)
+    , totalOut(0)
+    , zlibLevel(nSetLevel)
+{
+}
+
+ThreadedDeflater::~ThreadedDeflater() COVERITY_NOEXCEPT_FALSE { clear(); }
+
+void ThreadedDeflater::deflateWrite(
+    const css::uno::Reference<css::io::XInputStream>& xInStream,
+    std::function<void(const css::uno::Sequence<sal_Int8>&, sal_Int32)> aProcessInputFunc,
+    std::function<void(const css::uno::Sequence<sal_Int8>&, sal_Int32)> aProcessOutputFunc)
+{
+    sal_Int64 nThreadCount = comphelper::ThreadPool::getSharedOptimalPool().getWorkerCount();
+    sal_Int64 batchSize = MaxBlockSize * nThreadCount;
+    inBuffer.realloc(batchSize);
+    prevDataBlock.realloc(MaxBlockSize);
+    outBuffers.resize(nThreadCount);
+    maProcessOutputFunc = aProcessOutputFunc;
+    bool firstTask = true;
+
+    while (xInStream->available() > 0)
+    {
+        sal_Int64 inputBytes = xInStream->readBytes(inBuffer, batchSize);
+        aProcessInputFunc(inBuffer, inputBytes);
+        totalIn += inputBytes;
+        int sequence = 0;
+        bool lastBatch = xInStream->available() <= 0;
+        sal_Int64 bytesPending = inputBytes;
+        while (bytesPending > 0)
+        {
+            sal_Int64 taskSize = std::min(MaxBlockSize, bytesPending);
+            bytesPending -= taskSize;
+            bool lastTask = lastBatch && !bytesPending;
+            comphelper::ThreadPool::getSharedOptimalPool().pushTask(
+                std::make_unique<Task>(this, sequence++, taskSize, firstTask, lastTask));
+
+            if (firstTask)
+                firstTask = false;
+        }
+
+        assert(bytesPending == 0);
+
+        comphelper::ThreadPool::getSharedOptimalPool().waitUntilDone(threadTaskTag);
+
+        if (!lastBatch)
+        {
+            assert(inputBytes == batchSize);
+            std::copy_n(std::cbegin(inBuffer) + (batchSize - MaxBlockSize), MaxBlockSize,
+                        prevDataBlock.getArray());
+        }
+
+        processDeflatedBuffers();
+    }
+}
+
+void ThreadedDeflater::processDeflatedBuffers()
+{
+    sal_Int64 batchOutputSize = 0;
+    for (const auto& buffer : outBuffers)
+        batchOutputSize += buffer.size();
+
+    css::uno::Sequence<sal_Int8> outBuffer(batchOutputSize);
+
+    auto pos = outBuffer.getArray();
+    for (auto& buffer : outBuffers)
+    {
+        pos = std::copy(buffer.begin(), buffer.end(), pos);
+        buffer.clear();
+    }
+
+    maProcessOutputFunc(outBuffer, batchOutputSize);
+    totalOut += batchOutputSize;
+}
+
+void ThreadedDeflater::clear()
+{
+    inBuffer = uno::Sequence<sal_Int8>();
+    outBuffers.clear();
+}
+
+#if defined Z_PREFIX
+#define deflateInit2 z_deflateInit2
+#define deflateBound z_deflateBound
+#define deflateSetDictionary z_deflateSetDictionary
+#define deflate z_deflate
+#define deflateEnd z_deflateEnd
+#endif
+
+void ThreadedDeflater::Task::doWork()
+{
+    stream.zalloc = nullptr;
+    stream.zfree = nullptr;
+    stream.opaque = nullptr;
+    // -MAX_WBITS means 32k window size and raw stream
+    if (deflateInit2(&stream, deflater->zlibLevel, Z_DEFLATED, -MAX_WBITS, DEF_MEM_LEVEL,
+                     Z_DEFAULT_STRATEGY)
+        != Z_OK)
+    {
+        SAL_WARN("package.threadeddeflate", "deflateInit2() failed");
+        abort();
+    }
+    // Find out size for our output buffer to be large enough for deflate() needing to be called just once.
+    sal_Int64 outputMaxSize = deflateBound(&stream, blockSize);
+    // add extra size for Z_SYNC_FLUSH
+    outputMaxSize += 20;
+    deflater->outBuffers[sequence].resize(outputMaxSize);
+    sal_Int64 myInBufferStart = sequence * MaxBlockSize;
+    // zlib doesn't handle const properly
+    unsigned char* inBufferPtr = reinterpret_cast<unsigned char*>(
+        const_cast<signed char*>(deflater->inBuffer.getConstArray()));
+    if (!firstTask)
+    {
+        // the window size is 32k, so set last 32k of previous data as the dictionary
+        assert(MAX_WBITS == 15);
+        assert(MaxBlockSize >= 32768);
+        if (sequence > 0)
+        {
+            deflateSetDictionary(&stream, inBufferPtr + myInBufferStart - 32768, 32768);
+        }
+        else
+        {
+            unsigned char* prevBufferPtr = reinterpret_cast<unsigned char*>(
+                const_cast<signed char*>(deflater->prevDataBlock.getConstArray()));
+            deflateSetDictionary(&stream, prevBufferPtr + MaxBlockSize - 32768, 32768);
+        }
+    }
+    stream.next_in = inBufferPtr + myInBufferStart;
+    stream.avail_in = blockSize;
+    stream.next_out = reinterpret_cast<unsigned char*>(deflater->outBuffers[sequence].data());
+    stream.avail_out = outputMaxSize;
+
+    // The trick is in using Z_SYNC_FLUSH instead of Z_NO_FLUSH. It will align the data at a byte boundary,
+    // and since we use a raw stream, the data blocks then can be simply concatenated.
+    int res = deflate(&stream, lastTask ? Z_FINISH : Z_SYNC_FLUSH);
+    assert(stream.avail_in == 0); // Check that everything has been deflated.
+    if (lastTask ? res == Z_STREAM_END : res == Z_OK)
+    { // ok
+        sal_Int64 outSize = outputMaxSize - stream.avail_out;
+        deflater->outBuffers[sequence].resize(outSize);
+    }
+    else
+    {
+        SAL_WARN("package.threadeddeflate", "deflate() failed");
+        abort();
+    }
+    deflateEnd(&stream);
+}
+
+} // namespace
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */