use stack buffer in transliterateImpl

Change-Id: I7c3e24f3974dafeb9abb2af9e2a986003af7bfc1
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135873
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>

1 files changed, 14 insertions, 4 deletions

diff --git a/i18npool/source/transliteration/transliteration_body.cxx b/i18npool/source/transliteration/transliteration_body.cxx
index 605a3bb64284..69ba0c236714 100644
--- a/i18npool/source/transliteration/transliteration_body.cxx
+++ b/i18npool/source/transliteration/transliteration_body.cxx
@@ -121,8 +121,17 @@ Transliteration_body::transliterateImpl(
     // Yes, on massive use even such small things do count.
     if ( pOffset )
     {
-        std::vector<sal_Int32> aVec;
-        aVec.reserve(std::max<sal_Int32>(nLocalBuf, nCount) * NMAPPINGMAX);
+        sal_Int32* offsetData;
+        std::unique_ptr<sal_Int32[]> pOffsetHeapBuf;
+        sal_Int32 nOffsetCount = std::max<sal_Int32>(nLocalBuf, nCount);
+        if (nOffsetCount <= nLocalBuf)
+            offsetData = static_cast<sal_Int32*>(alloca(nOffsetCount * NMAPPINGMAX * sizeof(sal_Int32)));
+        else
+        {
+            pOffsetHeapBuf.reset(new sal_Int32[ nOffsetCount * NMAPPINGMAX ]);
+            offsetData = pOffsetHeapBuf.get();
+        }
+        sal_Int32* offsetDataEnd = offsetData;
 
         for (sal_Int32 i = 0; i < nCount; i++)
         {
@@ -130,12 +139,13 @@ Transliteration_body::transliterateImpl(
             MappingType nTmpMappingType = lcl_getMappingTypeForToggleCase( nMappingType, in[i] );
 
             const i18nutil::Mapping &map = i18nutil::casefolding::getValue( in, i, nCount, aLocale, nTmpMappingType );
-            std::fill_n(std::back_inserter(aVec), map.nmap, i + startPos);
+            std::fill_n(offsetDataEnd, map.nmap, i + startPos);
+            offsetDataEnd += map.nmap;
             std::copy_n(map.map, map.nmap, out + j);
             j += map.nmap;
         }
 
-        *pOffset = comphelper::containerToSequence(aVec);
+        *pOffset = css::uno::Sequence< sal_Int32 >(offsetData, offsetDataEnd - offsetData);
     }
     else
     {