TagSection: Split AlphaIndexes into AlphaIndexes and BetaIndexes

Move the use of the AlphaHash to a new second hash table in
preparation for the arrival of the new perfect hash function.

With the new perfect hash function hashing most of the keys for
us, having 128 slots for a fallback hash function seems enough
and prevents us from wasting space.

diff --git a/apt-pkg/tagfile.cc b/apt-pkg/tagfile.cc
index 69148e08baff1435fd6cb6382ca4a09a51b9539d..bf8320c31be47154b9c9e645186489e61d460189 100644 (file)
--- a/apt-pkg/tagfile.cc
+++ b/apt-pkg/tagfile.cc
@@ -98,7 +98,7 @@ public:
 };
                                                                        /*}}}*/
 
-static unsigned long AlphaHash(const char *Text, size_t Length)                /*{{{*/
+static unsigned long BetaHash(const char *Text, size_t Length)         /*{{{*/
 {
    /* This very simple hash function for the last 8 letters gives
       very good performance on the debian package files */
@@ -110,7 +110,7 @@ static unsigned long AlphaHash(const char *Text, size_t Length)             /*{{{*/
    unsigned long Res = 0;
    for (size_t i = 0; i < Length; ++i)
       Res = ((unsigned long)(Text[i]) & 0xDF) ^ (Res << 1);
-   return Res & 0xFF;
+   return Res & 0x7F;
 }
                                                                        /*}}}*/
 
@@ -474,6 +474,7 @@ pkgTagSection::pkgTagSection()
    : Section(0), d(new pkgTagSectionPrivate()), Stop(0)
 {
    memset(&AlphaIndexes, 0, sizeof(AlphaIndexes));
+   memset(&BetaIndexes, 0, sizeof(BetaIndexes));
 }
 APT_IGNORE_DEPRECATED_POP
                                                                        /*}}}*/
@@ -499,6 +500,7 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength, bool const R
       if (d->Tags.empty() == false)
       {
         memset(&AlphaIndexes, 0, sizeof(AlphaIndexes));
+        memset(&BetaIndexes, 0, sizeof(BetaIndexes));
         d->Tags.clear();
       }
       d->Tags.reserve(0x100);
@@ -526,10 +528,10 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength, bool const R
         // store the last found tag
         if (lastTagData.EndTag != 0)
         {
-           if (AlphaIndexes[lastTagHash] != 0)
-              lastTagData.NextInBucket = AlphaIndexes[lastTagHash];
+           if (BetaIndexes[lastTagHash] != 0)
+              lastTagData.NextInBucket = BetaIndexes[lastTagHash];
            APT_IGNORE_DEPRECATED_PUSH
-           AlphaIndexes[lastTagHash] = TagCount;
+           BetaIndexes[lastTagHash] = TagCount;
            APT_IGNORE_DEPRECATED_POP
            d->Tags.push_back(lastTagData);
         }
@@ -547,7 +549,7 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength, bool const R
            ;
         ++EndTag;
         lastTagData.EndTag = EndTag - Section;
-        lastTagHash = AlphaHash(Stop, EndTag - Stop);
+        lastTagHash = BetaHash(Stop, EndTag - Stop);
         // find the beginning of the value
         Stop = Colon + 1;
         for (; Stop < End && isspace_ascii(*Stop) != 0; ++Stop)
@@ -572,9 +574,9 @@ bool pkgTagSection::Scan(const char *Start,unsigned long MaxLength, bool const R
       {
         if (lastTagData.EndTag != 0)
         {
-           if (AlphaIndexes[lastTagHash] != 0)
-              lastTagData.NextInBucket = AlphaIndexes[lastTagHash];
-           APT_IGNORE_DEPRECATED(AlphaIndexes[lastTagHash] = TagCount;)
+           if (BetaIndexes[lastTagHash] != 0)
+              lastTagData.NextInBucket = BetaIndexes[lastTagHash];
+           APT_IGNORE_DEPRECATED(BetaIndexes[lastTagHash] = TagCount;)
            d->Tags.push_back(lastTagData);
         }
 
@@ -622,7 +624,7 @@ bool pkgTagSection::Find(StringView TagView,unsigned int &Pos) const
 {
    const char * const Tag = TagView.data();
    size_t const Length = TagView.length();
-   unsigned int Bucket = AlphaIndexes[AlphaHash(Tag, Length)];
+   unsigned int Bucket = BetaIndexes[BetaHash(Tag, Length)];
    if (Bucket == 0)
       return false;
 

diff --git a/apt-pkg/tagfile.h b/apt-pkg/tagfile.h
index 0f4c15436a1bd6c82dfcb969bf3a8a9a0211a6eb..f0f2f48c691f325db8a6c4ac0ce8e59c9899af61 100644 (file)
--- a/apt-pkg/tagfile.h
+++ b/apt-pkg/tagfile.h
@@ -49,7 +49,8 @@ class pkgTagFilePrivate;
 class pkgTagSection
 {
    const char *Section;
-   unsigned int AlphaIndexes[0x100];
+   unsigned int AlphaIndexes[128];
+   unsigned int BetaIndexes[128];
 
    pkgTagSectionPrivate * const d;