tdf#119992 sw: compare sub-strings in SwTextGlyphsKey comparison

Time till the layout reaches idle, before:

77.412 seconds

After:

26.221 seconds (33% of baseline) for me.

Change-Id: Idd0c5255070c836fde2fb048b02c851f5f2321e4
Reviewed-on: https://gerrit.libreoffice.org/61724
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins

1 files changed, 10 insertions, 3 deletions

diff --git a/sw/source/core/txtnode/fntcache.cxx b/sw/source/core/txtnode/fntcache.cxx
index 740710c6c27e..9166965dfb7e 100644
--- a/sw/source/core/txtnode/fntcache.cxx
+++ b/sw/source/core/txtnode/fntcache.cxx
@@ -144,9 +144,16 @@ bool operator<(const SwTextGlyphsKey& l, const SwTextGlyphsKey& r)
     if (l.m_nLength > r.m_nLength)
         return false;
 
-    // Comparing strings is expensive, so compare them only at the end, and
-    // only once.
-    sal_Int32 nRet = l.m_aText.compareTo(r.m_aText);
+    // Comparing strings is expensive, so compare them:
+    // - only at the end of this function
+    // - only once
+    // - only the relevant substring (if the index/length is not out of bounds)
+    sal_Int32 nRet = 0;
+    if (l.m_nLength < 0 || l.m_nIndex < 0 || l.m_nIndex + l.m_nLength > l.m_aText.getLength())
+        nRet = l.m_aText.compareTo(r.m_aText);
+    else
+        nRet = memcmp(l.m_aText.getStr() + l.m_nIndex, r.m_aText.getStr() + r.m_nIndex,
+                      l.m_nLength * sizeof(sal_Unicode));
     if (nRet < 0)
         return true;
     if (nRet > 0)