From 94c2fb28d76c9c37849412a66b31d6861bce3155 Mon Sep 17 00:00:00 2001
From: Luboš Luňák <l.lunak@collabora.com>
Date: Wed, 6 Apr 2022 19:28:07 +0200
Subject: faster hashing of very long strings in SalLayoutGlyphsCache
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tdf#147284 being a (pathological) testcase.

Change-Id: I08d8dffb40193b461555bed818c040761e8d575b
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/132669
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>
---
 vcl/inc/TextLayoutCache.hxx        | 32 ++++++++++++++++++++++++++++++++
 vcl/source/gdi/CommonSalLayout.cxx | 30 +-----------------------------
 vcl/source/gdi/impglyphitem.cxx    |  6 ++++--
 3 files changed, 37 insertions(+), 31 deletions(-)

diff --git a/vcl/inc/TextLayoutCache.hxx b/vcl/inc/TextLayoutCache.hxx
index 0ce0c19d8278..ecb85ea7043d 100644
--- a/vcl/inc/TextLayoutCache.hxx
+++ b/vcl/inc/TextLayoutCache.hxx
@@ -20,6 +20,8 @@
 #pragma once
 
 #include <sal/types.h>
+#include <rtl/ustring.hxx>
+#include <o3tl/hash_combine.hxx>
 
 #include <vcl/dllapi.h>
 
@@ -48,6 +50,36 @@ public:
     std::vector<vcl::text::Run> runs;
     TextLayoutCache(sal_Unicode const* pStr, sal_Int32 const nEnd);
 };
+
+struct FirstCharsStringHash
+{
+    size_t operator()(const OUString& str) const
+    {
+        // Strings passed to GenericSalLayout::CreateTextLayoutCache() may be very long,
+        // and computing an entire hash could almost negate the gain of hashing. Hash just first
+        // characters, that should be good enough.
+        size_t hash
+            = rtl_ustr_hashCode_WithLength(str.getStr(), std::min<size_t>(100, str.getLength()));
+        o3tl::hash_combine(hash, str.getLength());
+        return hash;
+    }
+};
+
+struct FastStringCompareEqual
+{
+    bool operator()(const OUString& str1, const OUString& str2) const
+    {
+        // Strings passed to GenericSalLayout::CreateTextLayoutCache() may be very long,
+        // and OUString operator == compares backwards and using hard-written code, while
+        // memcmp() compares much faster.
+        if (str1.getLength() != str2.getLength())
+            return false;
+        if (str1.getStr() == str2.getStr())
+            return true;
+        return memcmp(str1.getStr(), str2.getStr(), str1.getLength() * sizeof(str1.getStr()[0]))
+               == 0;
+    }
+};
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
diff --git a/vcl/source/gdi/CommonSalLayout.cxx b/vcl/source/gdi/CommonSalLayout.cxx
index 8dee28727997..2c8a4db8398f 100644
--- a/vcl/source/gdi/CommonSalLayout.cxx
+++ b/vcl/source/gdi/CommonSalLayout.cxx
@@ -154,40 +154,12 @@ namespace {
         return VerticalOrientation(nRet);
     }
 
-struct FirstCharsStringHash
-{
-    size_t operator()( const OUString& str ) const
-    {
-        // Strings passed to GenericSalLayout::CreateTextLayoutCache() may be very long,
-        // and computing an entire hash could almost negate the gain of hashing. Hash just first
-        // characters, that should be good enough.
-        size_t hash = rtl_ustr_hashCode_WithLength( str.getStr(), std::min<size_t>( 100, str.getLength()));
-        o3tl::hash_combine(hash, str.getLength());
-        return hash;
-    }
-};
-
-struct ForwardStringCompareEqual
-{
-    bool operator()( const OUString& str1, const OUString& str2 ) const
-    {
-        // Strings passed to GenericSalLayout::CreateTextLayoutCache() may be very long,
-        // and OUString operator == compares backwards, which is inefficient for very long
-        // strings (bad memory prefetch).
-        if( str1.getLength() != str2.getLength())
-            return false;
-        if( str1.getStr() == str2.getStr())
-            return true;
-        return memcmp( str1.getStr(), str2.getStr(), str1.getLength() * sizeof( str1.getStr()[ 0 ] )) == 0;
-    }
-};
-
 } // namespace
 
 std::shared_ptr<const vcl::text::TextLayoutCache> GenericSalLayout::CreateTextLayoutCache(OUString const& rString)
 {
     typedef o3tl::lru_map<OUString, std::shared_ptr<const vcl::text::TextLayoutCache>,
-        FirstCharsStringHash, ForwardStringCompareEqual> Cache;
+        vcl::text::FirstCharsStringHash, vcl::text::FastStringCompareEqual> Cache;
     static vcl::DeleteOnDeinit< Cache > cache( 1000 );
     if( Cache* map = cache.get())
     {
diff --git a/vcl/source/gdi/impglyphitem.cxx b/vcl/source/gdi/impglyphitem.cxx
index eaf8cf5c8453..d320d27dad88 100644
--- a/vcl/source/gdi/impglyphitem.cxx
+++ b/vcl/source/gdi/impglyphitem.cxx
@@ -21,6 +21,7 @@
 #include <vcl/glyphitemcache.hxx>
 #include <vcl/vcllayout.hxx>
 #include <tools/stream.hxx>
+#include <TextLayoutCache.hxx>
 
 SalLayoutGlyphs::SalLayoutGlyphs() {}
 
@@ -146,7 +147,7 @@ SalLayoutGlyphsCache::CachedGlyphsKey::CachedGlyphsKey(const VclPtr<const Output
     SvMemoryStream stream;
     WriteFont(stream, outputDevice->GetFont());
     o3tl::hash_combine(hashValue, static_cast<const char*>(stream.GetData()), stream.GetSize());
-    o3tl::hash_combine(hashValue, text);
+    o3tl::hash_combine(hashValue, vcl::text::FirstCharsStringHash()(text));
     o3tl::hash_combine(hashValue, index);
     o3tl::hash_combine(hashValue, len);
     o3tl::hash_combine(hashValue, logicPos.X());
@@ -158,7 +159,8 @@ inline bool SalLayoutGlyphsCache::CachedGlyphsKey::operator==(const CachedGlyphs
 {
     return hashValue == other.hashValue && outputDevice == other.outputDevice
            && index == other.index && len == other.len && logicPos == other.logicPos
-           && logicWidth == other.logicWidth && text == other.text;
+           && logicWidth == other.logicWidth
+           && vcl::text::FastStringCompareEqual()(text, other.text);
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
-- 
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