Avoid O(n*m) complexity in StringRef::find_first(_not)_of(StringRef).
- Cache used characters in a bitset to reduce memory overhead to just 32 bytes.
- On my core2 this code is faster except when the checked string was very short
(smaller than the list of delimiters).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@111817 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Support/StringRef.cpp b/lib/Support/StringRef.cpp
index ca0f518..40b732c 100644
--- a/lib/Support/StringRef.cpp
+++ b/lib/Support/StringRef.cpp
@@ -9,6 +9,7 @@
#include "llvm/ADT/StringRef.h"
#include "llvm/ADT/APInt.h"
+#include <bitset>
using namespace llvm;
@@ -153,11 +154,15 @@
/// find_first_of - Find the first character in the string that is in \arg
/// Chars, or npos if not found.
///
-/// Note: O(size() * Chars.size())
+/// Note: O(size() + Chars.size())
StringRef::size_type StringRef::find_first_of(StringRef Chars,
size_t From) const {
+ std::bitset<1 << CHAR_BIT> CharBits;
+ for (size_type i = 0; i != Chars.size(); ++i)
+ CharBits.set((unsigned char)Chars[i]);
+
for (size_type i = min(From, Length), e = Length; i != e; ++i)
- if (Chars.find(Data[i]) != npos)
+ if (CharBits.test((unsigned char)Data[i]))
return i;
return npos;
}
@@ -174,11 +179,15 @@
/// find_first_not_of - Find the first character in the string that is not
/// in the string \arg Chars, or npos if not found.
///
-/// Note: O(size() * Chars.size())
+/// Note: O(size() + Chars.size())
StringRef::size_type StringRef::find_first_not_of(StringRef Chars,
size_t From) const {
+ std::bitset<1 << CHAR_BIT> CharBits;
+ for (size_type i = 0; i != Chars.size(); ++i)
+ CharBits.set((unsigned char)Chars[i]);
+
for (size_type i = min(From, Length), e = Length; i != e; ++i)
- if (Chars.find(Data[i]) == npos)
+ if (!CharBits.test((unsigned char)Data[i]))
return i;
return npos;
}