Add a small LRU cache for the JBIG2 symbol dictionary.

core/src/fxcodec/jbig2/JBig2_Context.cpp

Index: core/src/fxcodec/jbig2/JBig2_Context.cpp
diff --git a/core/src/fxcodec/jbig2/JBig2_Context.cpp b/core/src/fxcodec/jbig2/JBig2_Context.cpp
index 83ded6fbe18f15ac81bde0b7d0de95d9b25ad2be..34a32c51389e4b54c08a05c15aa9014d54b013a3 100644
--- a/core/src/fxcodec/jbig2/JBig2_Context.cpp
+++ b/core/src/fxcodec/jbig2/JBig2_Context.cpp
@@ -4,7 +4,21 @@
  
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
+#include <map>
+#include <list>
 #include "JBig2_Context.h"
+
+// Implement a very small least recently used (LRU) cache. It is very
+// common for a JBIG2 dictionary to span multiple page in a PDF file,
+// and we do not want to decode the same dictionary over an over
+// again. We key off of the memory location of the dictionary. The
+// list keeps track of the freshness of enties, with freshest ones are
+// at the front. Even a tiny cache size like 2 makes a dramatic
+// difference for Google Books PDF files.
+const int kMaxCacheSize = 2;
+static std::map<FX_BYTE*, CJBig2_SymbolDict*> cache;
+static list<FX_BYTE*> cache_keys;
+
 void OutputBitmap(CJBig2_Image* pImage)
 {
     if(!pImage) {
@@ -614,6 +628,7 @@ FX_INT32 CJBig2_Context::parseSymbolDict(CJBig2_Segment *pSegment, IFX_Pause* pP
     JBig2ArithCtx *gbContext = NULL, *grContext = NULL;
     CJBig2_ArithDecoder *pArithDecoder;
     JBIG2_ALLOC(pSymbolDictDecoder, CJBig2_SDDProc());
+    FX_BYTE *key = pSegment->m_pData;
     if(m_pStream->readShortInteger(&wFlags) != 0) {
         m_pModule->JBig2_Error("symbol dictionary segment : data header too short.");
         nRet = JBIG2_ERROR_TOO_SHORT;
@@ -791,7 +806,17 @@ FX_INT32 CJBig2_Context::parseSymbolDict(CJBig2_Segment *pSegment, IFX_Pause* pP
         }
     }
     pSegment->m_nResultType = JBIG2_SYMBOL_DICT_POINTER;
-    if(pSymbolDictDecoder->SDHUFF == 0) {
+    if (cache.find(key) != cache.end()) {
+        pSegment->m_Result.sd = cache[key]->DeepCopy();
+        for(std::list<FX_BYTE*>::iterator it = cache_keys.begin();

[Bo Xu, 2014/12/08 23:00:17]

Nit: set tab size to 4

[jab, 2014/12/08 23:21:04]

Done.

+            it != cache_keys.end(); ++it) {
+          if (*it == key) {
+            cache_keys.erase(it);
+            break;
+          }
+        }
+        cache_keys.push_front(key);
+    } else if(pSymbolDictDecoder->SDHUFF == 0) {
         JBIG2_ALLOC(pArithDecoder, CJBig2_ArithDecoder(m_pStream));
         pSegment->m_Result.sd = pSymbolDictDecoder->decode_Arith(pArithDecoder, gbContext, grContext);
         delete pArithDecoder;
@@ -809,6 +834,18 @@ FX_INT32 CJBig2_Context::parseSymbolDict(CJBig2_Segment *pSegment, IFX_Pause* pP
         }
         m_pStream->alignByte();
     }
+    if (cache.find(key) == cache.end()) {
+        CJBig2_SymbolDict *value = pSegment->m_Result.sd->DeepCopy();
+        if (value) {
+            while (cache_keys.size() >= kMaxCacheSize) {
+                // Destroy cache(cache_keys.back());
+                cache.erase(cache_keys.back());
+                cache_keys.pop_back();
+            }
+            cache.insert(std::pair<FX_BYTE*, CJBig2_SymbolDict*>(key, value));
+            cache_keys.push_front(key);
+        }
+    }
     if(wFlags & 0x0200) {
         pSegment->m_Result.sd->m_bContextRetained = TRUE;
         if(pSymbolDictDecoder->SDHUFF == 0) {