Do not use MD5SumValue for Description_md5()

Our profile says we spend about 5% of the time transforming the
hex digits into the binary format used by HashsumValue, all for
comparing them against the other strings. That makes no sense
at all.

According to callgrind, this reduces the overall instruction
count from 5,3 billion to 5 billion in my example, which
roughly matches the 5%.

2 files changed, 11 insertions, 12 deletions

diff --git a/apt-pkg/deb/deblistparser.cc b/apt-pkg/deb/deblistparser.cc
index ea4d8e063..0fc08d8fb 100644
--- a/apt-pkg/deb/deblistparser.cc
+++ b/apt-pkg/deb/deblistparser.cc
@@ -276,31 +276,27 @@ std::vector<std::string> debListParser::AvailableDescriptionLanguages()
    description. If no Description-md5 is found in the section it will be
    calculated.
  */
-MD5SumValue debListParser::Description_md5()
+APT::StringView debListParser::Description_md5()
 {
    StringView const value = Section.Find(pkgTagSection::Key::Description_md5);
-   if (value.empty() == true)
+   if (unlikely(value.empty() == true))
    {
       StringView const desc = Section.Find(pkgTagSection::Key::Description);
       if (desc == "\n")
-	 return MD5SumValue();
+	 return StringView();
 
       MD5Summation md5;
       md5.Add(desc.data(), desc.size());
       md5.Add("\n");
-      return md5.Result();
+      MD5Buffer = md5.Result();
+      return StringView(MD5Buffer);
    }
    else if (likely(value.size() == 32))
    {
-      MD5SumValue sumvalue;
-      if (sumvalue.Set(value))
-	 return sumvalue;
-
-      _error->Error("Malformed Description-md5 line; includes invalid character '%.*s'", (int)value.length(), value.data());
-      return MD5SumValue();
+      return value;
    }
    _error->Error("Malformed Description-md5 line; doesn't have the required length (32 != %d) '%.*s'", (int)value.size(), (int)value.length(), value.data());
-   return MD5SumValue();
+   return StringView();
 }
                                                                         /*}}}*/
 // ListParser::UsePackage - Update a package structure			/*{{{*/
diff --git a/apt-pkg/deb/deblistparser.h b/apt-pkg/deb/deblistparser.h
index 43ce0cfd3..3d5065953 100644
--- a/apt-pkg/deb/deblistparser.h
+++ b/apt-pkg/deb/deblistparser.h
@@ -45,6 +45,7 @@ class APT_HIDDEN debListParser : public pkgCacheListParser
    private:
    std::vector<std::string> forceEssential;
    std::vector<std::string> forceImportant;
+   std::string MD5Buffer;
 
    protected:
    pkgTagFile Tags;
@@ -74,7 +75,9 @@ class APT_HIDDEN debListParser : public pkgCacheListParser
 #endif
    virtual bool NewVersion(pkgCache::VerIterator &Ver) APT_OVERRIDE;
    virtual std::vector<std::string> AvailableDescriptionLanguages() APT_OVERRIDE;
-   virtual MD5SumValue Description_md5() APT_OVERRIDE;
+#ifdef APT_PKG_EXPOSE_STRING_VIEW
+   virtual APT::StringView Description_md5() APT_OVERRIDE;
+#endif
    virtual unsigned short VersionHash() APT_OVERRIDE;
    virtual bool SameVersion(unsigned short const Hash, pkgCache::VerIterator const &Ver) APT_OVERRIDE;
    virtual bool UsePackage(pkgCache::PkgIterator &Pkg,