Avoid COW overhead using css::uno::Sequence

The scenarios are:

1. Calling sequence's begin() and end() in pairs to pass to algorithms
(both calls use getArray(), which does the COW checks)
2. In addition to #1, calling end() again when checking result of find
algorithms, and/or begin() to calculate result's distance
3. Using non-const sequences in range-based for loops, which internally
do #1
4. Assigning sequence to another sequence variable, and then modifying
one of them

In many cases, the sequences could be made const, or treated as const
for the purposes of the algorithms (using std::as_const, std::cbegin,
and std::cend). Where algorithm modifies the sequence, it was changed
to only call getArray() once. For that, css::uno::toNonConstRange was
introduced, which returns a struct (sublclass of std::pair) with two
iterators [begin, end], that are calculated using one call to begin()
and one call to getLength().

To handle #4, css::uno::Sequence::swap was introduced, that swaps the
internal pointer to uno_Sequence. So when a local Sequence variable
should be assigned to another variable, and the latter will be modified
further, it's now possible to use swap instead, so the two sequences
are kept independent.

The modified places were found by temporarily removing non-const end().

Change-Id: I8fe2787f200eecb70744e8b77fbdf7a49653f628
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/123542
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>

4 files changed, 5 insertions, 7 deletions

diff --git a/oox/source/crypto/AgileEngine.cxx b/oox/source/crypto/AgileEngine.cxx
index 63712d01b3ef..0fd655ced63c 100644
--- a/oox/source/crypto/AgileEngine.cxx
+++ b/oox/source/crypto/AgileEngine.cxx
@@ -504,7 +504,7 @@ bool AgileEngine::readEncryptionInfo(uno::Reference<io::XInputStream> & rxInputS
     uno::Sequence<sal_Int8> aReadReservedBytes(sizeof(sal_uInt32));
     rxInputStream->readBytes(aReadReservedBytes, aReadReservedBytes.getLength());
 
-    if (!std::equal(aReadReservedBytes.begin(), aReadReservedBytes.end(), aExpectedReservedBytes.begin()))
+    if (!std::equal(std::cbegin(aReadReservedBytes), std::cend(aReadReservedBytes), aExpectedReservedBytes.begin()))
         return false;
 
     mInfo.spinCount = 0;
diff --git a/oox/source/export/chartexport.cxx b/oox/source/export/chartexport.cxx
index 452b5f5ef851..32736e67fad0 100644
--- a/oox/source/export/chartexport.cxx
+++ b/oox/source/export/chartexport.cxx
@@ -406,7 +406,7 @@ static void lcl_fillCategoriesIntoStringVector(
     if( xTextualDataSequence.is())
     {
         rOutCategories.clear();
-        Sequence< OUString > aTextData( xTextualDataSequence->getTextualData());
+        const Sequence< OUString > aTextData( xTextualDataSequence->getTextualData());
         rOutCategories.insert( rOutCategories.end(), aTextData.begin(), aTextData.end() );
     }
     else
@@ -425,7 +425,7 @@ static ::std::vector< double > lcl_getAllValuesFromSequence( const Reference< ch
     Reference< chart2::data::XNumericalDataSequence > xNumSeq( xSeq, uno::UNO_QUERY );
     if( xNumSeq.is())
     {
-        Sequence< double > aValues( xNumSeq->getNumericalData());
+        const Sequence< double > aValues( xNumSeq->getNumericalData());
         aResult.insert( aResult.end(), aValues.begin(), aValues.end() );
     }
     else if( xSeq.is())
diff --git a/oox/source/helper/zipstorage.cxx b/oox/source/helper/zipstorage.cxx
index 987ab3b809d1..d11d145bb764 100644
--- a/oox/source/helper/zipstorage.cxx
+++ b/oox/source/helper/zipstorage.cxx
@@ -110,10 +110,9 @@ Reference< XStorage > ZipStorage::implGetXStorage() const
 
 void ZipStorage::implGetElementNames( ::std::vector< OUString >& orElementNames ) const
 {
-    Sequence< OUString > aNames;
     if( mxStorage.is() ) try
     {
-        aNames = mxStorage->getElementNames();
+        const Sequence<OUString> aNames = mxStorage->getElementNames();
         if( aNames.hasElements() )
             orElementNames.insert( orElementNames.end(), aNames.begin(), aNames.end() );
     }
diff --git a/oox/source/ole/olestorage.cxx b/oox/source/ole/olestorage.cxx
index 82aa1cd79fe8..32673fa699af 100644
--- a/oox/source/ole/olestorage.cxx
+++ b/oox/source/ole/olestorage.cxx
@@ -279,10 +279,9 @@ Reference< XStorage > OleStorage::implGetXStorage() const
 
 void OleStorage::implGetElementNames( ::std::vector< OUString >& orElementNames ) const
 {
-    Sequence< OUString > aNames;
     if( mxStorage.is() ) try
     {
-        aNames = mxStorage->getElementNames();
+        const Sequence<OUString> aNames = mxStorage->getElementNames();
         if( aNames.hasElements() )
             orElementNames.insert( orElementNames.end(), aNames.begin(), aNames.end() );
     }