db/simple/Directory: optimize GetName() using the parent's path

This method gets called a lot during MPD startup, via FindChild() and directory_load_subdir(), so this is worth optimizing at the expense of code readability. This speeds up MPD startup by 10%.

db/simple/Directory: optimize GetName() using the parent's path
cdddaf21 · Max Kellermann · b267ba5f · cdddaf21
Commit cdddaf21 authored Apr 02, 2020 by Max Kellermann
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Directory.cxx src/db/plugins/simple/Directory.cxx +10 -1

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--- a/src/db/plugins/simple/Directory.cxx
+++ b/src/db/plugins/simple/Directory.cxx
@@ -32,6 +32,7 @@
 #include "fs/Traits.hxx"
 #include "util/Alloc.hxx"
 #include "util/DeleteDisposer.hxx"
+#include "util/StringCompare.hxx"

 #include <assert.h>
 #include <string.h>
@@ -69,7 +70,15 @@ Directory::GetName() const noexcept
 {
 	assert(!IsRoot());

-	return PathTraitsUTF8::GetBase(path.c_str());
+	if (parent->IsRoot())
+		return path.c_str();
+
+	assert(StringAfterPrefix(path.c_str(), parent->path.c_str()) != nullptr);
+	assert(*StringAfterPrefix(path.c_str(), parent->path.c_str()) == PathTraitsUTF8::SEPARATOR);
+
+	/* strip the parent directory path and the slash separator
+	   from this directory's path, and the base name remains */
+	return path.c_str() + parent->path.length() + 1;
 }

 Directory *