Bug 559715: Micro-optimize nsCSSPropertySet by adjusting types so tha…

…t the compiler can do index calculations more efficiently., r=dbaron, a=dholbert_sheriff
dothq · Apr 23, 2010 · 590227c · 590227c
1 parent 9a2068c
commit 590227c
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Showing 2 changed files with 30 additions and 24 deletions.
diff --git a/layout/style/nsCSSDataBlock.cpp b/layout/style/nsCSSDataBlock.cpp
@@ -714,10 +714,10 @@ nsCSSExpandedDataBlock::ComputeSizeResult
 nsCSSExpandedDataBlock::ComputeSize()
 {
     ComputeSizeResult result = {0, 0};
-    for (PRUint32 iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
+    for (size_t iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
         if (!mPropertiesSet.HasPropertyInChunk(iHigh))
             continue;
-        for (PRInt32 iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
+        for (size_t iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
             if (!mPropertiesSet.HasPropertyAt(iHigh, iLow))
                 continue;
             nsCSSProperty iProp = nsCSSPropertySet::CSSPropertyAt(iHigh, iLow);
@@ -808,10 +808,10 @@ nsCSSExpandedDataBlock::Compress(nsCSSCompressedDataBlock **aNormalBlock,
      * corresponding to the stored data in the expanded block, and then
      * clearing the data in the expanded block.
      */
-    for (PRUint32 iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
+    for (size_t iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
         if (!mPropertiesSet.HasPropertyInChunk(iHigh))
             continue;
-        for (PRInt32 iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
+        for (size_t iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
             if (!mPropertiesSet.HasPropertyAt(iHigh, iLow))
                 continue;
             nsCSSProperty iProp = nsCSSPropertySet::CSSPropertyAt(iHigh, iLow);
@@ -896,10 +896,10 @@ nsCSSExpandedDataBlock::Compress(nsCSSCompressedDataBlock **aNormalBlock,
 void
 nsCSSExpandedDataBlock::Clear()
 {
-    for (PRUint32 iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
+    for (size_t iHigh = 0; iHigh < nsCSSPropertySet::kChunkCount; ++iHigh) {
         if (!mPropertiesSet.HasPropertyInChunk(iHigh))
             continue;
-        for (PRInt32 iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
+        for (size_t iLow = 0; iLow < nsCSSPropertySet::kBitsInChunk; ++iLow) {
             if (!mPropertiesSet.HasPropertyAt(iHigh, iLow))
                 continue;
             nsCSSProperty iProp = nsCSSPropertySet::CSSPropertyAt(iHigh, iLow);

diff --git a/layout/style/nsCSSPropertySet.h b/layout/style/nsCSSPropertySet.h
@@ -40,6 +40,7 @@
 #define nsCSSPropertySet_h__
 
 #include "nsCSSProperty.h"
+#include <limits.h> // for CHAR_BIT
 
 /**
  * nsCSSPropertySet maintains a set of non-shorthand CSS properties.  In
@@ -57,56 +58,61 @@ class nsCSSPropertySet {
                      "out of bounds");
     }
 
+    // Conversion of aProperty to |size_t| after AssertInSetRange
+    // lets the compiler generate significantly tighter code.
+
     void AddProperty(nsCSSProperty aProperty) {
         AssertInSetRange(aProperty);
-        mProperties[aProperty / kBitsInChunk] |=
-            property_set_type(1 << (aProperty % kBitsInChunk));
+        size_t p = aProperty;
+        mProperties[p / kBitsInChunk] |=
+          property_set_type(1) << (p % kBitsInChunk);
     }
 
     void RemoveProperty(nsCSSProperty aProperty) {
         AssertInSetRange(aProperty);
-        mProperties[aProperty / kBitsInChunk] &=
-            ~property_set_type(1 << (aProperty % kBitsInChunk));
+        size_t p = aProperty;
+        mProperties[p / kBitsInChunk] &=
+            ~(property_set_type(1) << (p % kBitsInChunk));
     }
 
-    PRBool HasProperty(nsCSSProperty aProperty) const {
+    bool HasProperty(nsCSSProperty aProperty) const {
         AssertInSetRange(aProperty);
-        return (mProperties[aProperty / kBitsInChunk] &
-                (1 << (aProperty % kBitsInChunk))) != 0;
+        size_t p = aProperty;
+        return (mProperties[p / kBitsInChunk] &
+                (property_set_type(1) << (p % kBitsInChunk))) != 0;
     }
 
     void Empty() {
         memset(mProperties, 0, sizeof(mProperties));
     }
 
     void AssertIsEmpty(const char* aText) const {
-        for (PRUint32 i = 0; i < NS_ARRAY_LENGTH(mProperties); ++i) {
+        for (size_t i = 0; i < NS_ARRAY_LENGTH(mProperties); ++i) {
             NS_ASSERTION(mProperties[i] == 0, aText);
         }
     }
 
 private:
-    typedef PRUint8 property_set_type;
+    typedef unsigned long property_set_type;
 public:
-    enum { kBitsInChunk = 8 }; // number of bits in
-                                          // |property_set_type|.
+    // number of bits in |property_set_type|.
+    static const size_t kBitsInChunk = sizeof(property_set_type)*CHAR_BIT;
     // number of |property_set_type|s in the set
-    enum { kChunkCount =
-             (eCSSProperty_COUNT_no_shorthands + (kBitsInChunk-1)) /
-             kBitsInChunk };
+    static const size_t kChunkCount =
+        (eCSSProperty_COUNT_no_shorthands + kBitsInChunk - 1) / kBitsInChunk;
 
     /*
      * For fast enumeration of all the bits that are set, callers can
      * check each chunk against zero (since in normal cases few bits are
      * likely to be set).
      */
-    PRBool HasPropertyInChunk(PRUint32 aChunk) const {
+    bool HasPropertyInChunk(size_t aChunk) const {
         return mProperties[aChunk] != 0;
     }
-    PRBool HasPropertyAt(PRUint32 aChunk, PRInt32 aBit) const {
-        return (mProperties[aChunk] & (1 << aBit)) != 0;
+    bool HasPropertyAt(size_t aChunk, size_t aBit) const {
+        return (mProperties[aChunk] & (property_set_type(1) << aBit)) != 0;
     }
-    static nsCSSProperty CSSPropertyAt(PRUint32 aChunk, PRInt32 aBit) {
+    static nsCSSProperty CSSPropertyAt(size_t aChunk, size_t aBit) {
         return nsCSSProperty(aChunk * kBitsInChunk + aBit);
     }