Reimplement boost::split_iterator to make it less slow

boost::split_iterator type-erases the predicate, which makes it require
a virtual call per character (!) along with a heap allocation. As it
turns out we only ever need one predicate (comparing to a single
character), so replace it with a split_iterator that just does that.

libaegisub/include/libaegisub/split.h

@@ -1,4 +1,4 @@
-// Copyright (c) 2013, Thomas Goyne <plorkyeran@aegisub.org>
+// Copyright (c) 2015, Thomas Goyne <plorkyeran@aegisub.org>
 //
 // Permission to use, copy, modify, and distribute this software for any
 // purpose with or without fee is hereby granted, provided that the above
@@ -14,32 +14,89 @@
 //
 // Aegisub Project http://www.aegisub.org/
 
-#include <boost/algorithm/string/finder.hpp>
-#include <boost/algorithm/string/split.hpp>
+#include <boost/range/iterator_range.hpp>
 
 namespace agi {
 	typedef boost::iterator_range<std::string::const_iterator> StringRange;
 
+	template<typename Iterator>
+	class split_iterator {
+		bool is_end = false;
+		Iterator b;
+		Iterator cur;
+		Iterator e;
+		typename Iterator::value_type c;
+
+	public:
+		using iterator_category = std::forward_iterator_tag;
+		using value_type = boost::iterator_range<Iterator>;
+		using pointer = value_type*;
+		using reference = value_type&;
+		using difference_type = ptrdiff_t;
+
+		split_iterator(Iterator begin, Iterator end, typename Iterator::value_type c)
+		: b(begin), cur(begin), e(end), c(c)
+		{
+			if (b != e)
+				cur = std::find(b, e, c);
+			else
+				is_end = true;
+		}
+
+		split_iterator() : is_end(true) { }
+
+		bool eof() const { return is_end; }
+
+		boost::iterator_range<Iterator> operator*() const {
+			return boost::make_iterator_range(b, cur);
+		}
+
+		bool operator==(split_iterator const& it) const {
+			if (is_end || it.is_end)
+				return is_end && it.is_end;
+			return b == it.b && cur == it.cur && e == it.e && c == it.c;
+		}
+
+		bool operator!=(split_iterator const& it) const {
+			return !(*this == it);
+		}
+
+		split_iterator& operator++() {
+			if (cur != e) {
+				b = cur + 1;
+				cur = std::find(b, e, c);
+			}
+			else {
+				b = e;
+				is_end = true;
+			}
+
+			return *this;
+		}
+
+		split_iterator operator++(int) {
+			split_iterator tmp = *this;
+			++*this;
+			return tmp;
+		}
+	};
+
+	template<typename Iterator>
+	split_iterator<Iterator> begin(split_iterator<Iterator> const& it) {
+		return it;
+	}
+
+	template<typename Iterator>
+	split_iterator<Iterator> end(split_iterator<Iterator> const&) {
+		return split_iterator<Iterator>();
+	}
+
 	template<typename Str, typename Char>
-	boost::split_iterator<typename Str::const_iterator> Split(Str const& str, Char delim) {
-		return boost::make_split_iterator(str, boost::token_finder([=](Char c) { return c == delim; }));
+	split_iterator<typename Str::const_iterator> Split(Str const& str, Char delim) {
+		return split_iterator<typename Str::const_iterator>(begin(str), end(str), delim);
 	}
 
 	static inline std::string str(StringRange const& r) {
 		return std::string(r.begin(), r.end());
 	}
 }
-
-namespace boost {
-	namespace algorithm {
-		template<typename Iterator>
-		split_iterator<Iterator> begin(split_iterator<Iterator> it) {
-			return it;
-		}
-
-		template<typename Iterator>
-		split_iterator<Iterator> end(split_iterator<Iterator>) {
-			return split_iterator<Iterator>();
-		}
-	}
-}

src/ass_dialogue.cpp

@@ -73,7 +73,7 @@ AssDialogue::~AssDialogue () { }
 
 class tokenizer {
 	agi::StringRange str;
-	boost::split_iterator<agi::StringRange::const_iterator> pos;
+	agi::split_iterator<agi::StringRange::const_iterator> pos;
 
 public:
 	tokenizer(agi::StringRange const& str) : str(str) , pos(agi::Split(str, ',')) { }

src/ass_style.cpp

@@ -54,7 +54,7 @@ AssEntryGroup AssStyle::Group() const { return AssEntryGroup::STYLE; }
 
 namespace {
 class parser {
-	boost::split_iterator<agi::StringRange::const_iterator> pos;
+	agi::split_iterator<agi::StringRange::const_iterator> pos;
 
 	std::string next_tok() {
 		if (pos.eof())

tests/tests/split.cpp

@@ -41,7 +41,7 @@ TEST(lagi_split, does_not_copy_input) {
 	}
 
 	auto rng = agi::Split(str, 'e');
-	EXPECT_EQ(str.begin(), rng->begin());
-	EXPECT_EQ(str.end(), std::next(rng)->end());
+	EXPECT_EQ(str.begin(), begin(*rng));
+	EXPECT_EQ(str.end(), end(*std::next(rng)));
 }