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.

2 files changed, 14 insertions, 11 deletions

diff --git a/apt-pkg/tagfile.cc b/apt-pkg/tagfile.cc
index 69148e08b..bf8320c31 100644
--- 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 0f4c15436..f0f2f48c6 100644
--- 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;