From 8d84ec6d1c40ed2769556c3642bd4fa785c1905c Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Sun, 17 Jun 2018 14:01:38 +0100
Subject: Massively simplified CTF with C++17 constexpr

---
 libadhocutil/compileTimeFormatter.h | 194 +++++++++---------------------------
 1 file changed, 48 insertions(+), 146 deletions(-)

diff --git a/libadhocutil/compileTimeFormatter.h b/libadhocutil/compileTimeFormatter.h
index d55012e..4b268f7 100644
--- a/libadhocutil/compileTimeFormatter.h
+++ b/libadhocutil/compileTimeFormatter.h
@@ -34,61 +34,35 @@ namespace AdHoc {
 		return off;
 	}
 
-	/// @cond
-	inline constexpr int WRAP_AT = 120;
+	template <const char * const &, auto> class Formatter;
 
-	namespace FormatterImpl {
-		template <bool, char...> struct ParserBuffer { };
-		template <int, char...> struct Buffer { };
-	}
-
-	template <const char * const & S, int start, typename stream, char ... sn>
+	template<const char * const & S, auto L, auto pos, typename stream, char ...>
 	struct StreamWriter {
-		template<typename ... Pn>
-		static void write(stream & s, const Pn & ... pn);
-
-		template<typename ... Pn, int len, char... ssn, template <int, char...> class Buffer>
-		static void next(stream & s, const Buffer<len, ssn...>&, const Pn & ... pn)
-		{
-			StreamWriter<S, start + len, stream, ssn...>::write(s, pn...);
-		}
-	};
-
-	template<const char * const & S, int start, typename stream>
-	struct StreamWriter<S, start, stream> {
-		template<typename ... Pn>
-		static void write(stream &, const Pn & ...) { }
 	};
 
-	template<const char * const & S, int start, typename stream>
-	struct StreamWriter<S, start, stream, 0> {
-		template<typename ... Pn>
-		static void write(stream &, const Pn & ...) { }
-	};
-
-	template<const char * const & S, int start, int len, typename stream, char ... sn>
+	template<const char * const & S, auto L, auto pos, typename stream>
 	struct StreamWriterBase {
 		template<typename ... Pn>
-		static void next(stream & s, const Pn & ... pn)
+		static inline void next(stream & s, const Pn & ... pn)
 		{
-			StreamWriter<S, start + len, stream, sn...>::write(s, pn...);
+			Formatter<S, L>::template Parser<stream, pos + 1, Pn...>::run(s, pn...);
 		}
 	};
 
 #define StreamWriterT(C...) \
-	template<const char * const & S, int start, typename stream, char ... sn> \
-	struct StreamWriter<S, start, stream, '%', C, sn...> : \
-		public StreamWriterBase<S, start, BOOST_PP_VARIADIC_SIZE(C) + 1, stream, sn...>
+	template<const char * const & S, auto L, auto pos, typename stream, char ... sn> \
+	struct StreamWriter<S, L, pos, stream, '%', C, sn...> : \
+		public StreamWriterBase<S, L, BOOST_PP_VARIADIC_SIZE(C) + pos, stream>
 
 #define StreamWriterTP(P, C...) \
-	template<const char * const & S, int start, typename stream, char P, char ... sn> \
-	struct StreamWriter<S, start, stream, '%', C, sn...> : \
-		public StreamWriterBase<S, start, BOOST_PP_VARIADIC_SIZE(C) + 1, stream, sn...>
+	template<const char * const & S, auto L, auto pos, typename stream, char P, char ... sn> \
+	struct StreamWriter<S, L, pos, stream, '%', C, sn...> : \
+		public StreamWriterBase<S, L, BOOST_PP_VARIADIC_SIZE(C) + pos, stream>
 
 	// Default stream writer formatter
 	StreamWriterT('?') {
 		template<typename P, typename ... Pn>
-		static void write(stream & s, const P & p, const Pn & ... pn)
+		static inline void write(stream & s, const P & p, const Pn & ... pn)
 		{
 			s << p;
 			StreamWriter::next(s, pn...);
@@ -98,7 +72,7 @@ namespace AdHoc {
 	// Escaped % stream writer formatter
 	StreamWriterT('%') {
 		template<typename ... Pn>
-		static void write(stream & s, const Pn & ... pn)
+		static inline void write(stream & s, const Pn & ... pn)
 		{
 			s << '%';
 			StreamWriter::next(s, pn...);
@@ -106,8 +80,8 @@ namespace AdHoc {
 	};
 
 	// Unknown stream writer formatter
-	template<const char * const & S, int start, typename stream, char ... sn>
-	struct StreamWriter<S, start, stream, '%', sn...> {
+	template<const char * const & S, auto L, auto pos, typename stream, char ... sn>
+	struct StreamWriter<S, L, pos, stream, '%', sn...> {
 		template<typename ... Pn>
 		static void write(stream &, const Pn & ...)
 		{
@@ -120,94 +94,10 @@ namespace AdHoc {
 	 * Compile time string formatter.
 	 * @param S the format string.
 	 */
-	template <const char * const & S>
+	template <const char * const & S, auto L = strlen<S>()>
 	class Formatter {
 		private:
-			template<const char * const &, int, typename, char ...> friend struct StreamWriter;
-
-			template <int start, int offset, char ...>
-			struct Upto {
-				template<typename stream>
-				static auto scan(stream &, const FormatterImpl::Buffer<start> & f)
-				{
-					return f;
-				}
-			};
-			template <int start, int offset, char s0, char... sn>
-			struct Upto<start, offset, s0, sn...> {
-				template<typename stream, int len, char... sm>
-				static auto scan(stream & s, const FormatterImpl::Buffer<len, sm...> &)
-				{
-					return Upto<start, offset + 1, sn...>::scan(s, FormatterImpl::Buffer<len, sm..., s0>());
-				}
-			};
-			template <int start, char... sn>
-			struct UptoWrite {
-				template<typename stream, int len, char... sm>
-				static auto scan(stream & s, const FormatterImpl::Buffer<len, sm...> &)
-				{
-					s.write(S + start, sizeof...(sm));
-					return FormatterImpl::Buffer<sizeof...(sm), sn...>();
-				}
-			};
-			template <int start, int offset, char... sn>
-			struct Upto<start, offset, '%', sn...> : public UptoWrite<start, '%', sn...> { };
-			template <int start, int offset, char... sn>
-			struct Upto<start, offset, 0, sn...> : public UptoWrite<start, 0, sn...> { };
-			template <int start, char s0, char... sn>
-			struct Upto<start, WRAP_AT, s0, sn...> : public UptoWrite<start, s0, sn...> { };
-			template <int start, char... sn>
-			struct Upto<start, WRAP_AT, '%', sn...> : public UptoWrite<start, '%', sn...> { };
-			template <int start, char... sn>
-			struct Upto<start, WRAP_AT, 0, sn...> : public UptoWrite<start, 0, sn...> { };
-
-			template <int offset, int roffset, char s0, char ... sn>
-			struct Parser {
-				static auto parse()
-				{
-					return append(innerparse());
-				}
-				static auto innerparse()
-				{
-					return Parser<offset + 1, roffset + 1, S[offset + 1], sn..., s0>::innerparse();
-				}
-				template<char...ssn>
-				static auto append(const FormatterImpl::ParserBuffer<true, ssn...> & b)
-				{
-					return join(b, Parser<offset + 1 + WRAP_AT, 0, S[offset + 1 + WRAP_AT]>::parse());
-				}
-				template<char...ssn>
-				static auto append(const FormatterImpl::ParserBuffer<false, ssn...> & b)
-				{
-					return b;
-				}
-				template<bool more, char...ssn, char...ssm>
-				static auto join(const FormatterImpl::ParserBuffer<true, ssn...> &, const FormatterImpl::ParserBuffer<more, ssm...> &)
-				{
-					return FormatterImpl::ParserBuffer<more, ssn..., ssm...>();
-				}
-			};
-
-			template <bool more, char ... sn>
-			struct ParserBase {
-				static auto parse()
-				{
-					return innerparse();
-				}
-				static auto innerparse()
-				{
-					return FormatterImpl::ParserBuffer<more, sn...>();
-				}
-			};
-
-			template <int offset, char s0, char ... sn>
-			struct Parser<offset, WRAP_AT, s0, sn...> : public ParserBase<true, sn..., s0> { };
-
-			template <int offset, char ... sn>
-			struct Parser<offset, WRAP_AT, 0, sn...> : public ParserBase<true, sn..., 0> { };
-
-			template <int offset, int roffset, char ... sn>
-			struct Parser<offset, roffset, 0, sn...> : public ParserBase<false, sn..., 0>{ };
+			template<const char * const &, auto, auto, typename> friend struct StreamWriterBase;
 
 		public:
 			/**
@@ -216,10 +106,10 @@ namespace AdHoc {
 			 * @return the formatted string.
 			 */
 			template<typename ... Pn>
-			static std::string get(const Pn & ... pn)
+			static inline std::string get(const Pn & ... pn)
 			{
 				std::stringstream s;
-				return run(Parser<0, 0, *S>::parse(), s, pn...).str();
+				return write(s, pn...).str();
 			}
 
 			/**
@@ -229,28 +119,40 @@ namespace AdHoc {
 			 * @return the stream.
 			 */
 			template<typename stream, typename ... Pn>
-			static stream & write(stream & s, const Pn & ... pn)
+			static inline stream & write(stream & s, const Pn & ... pn)
 			{
-				return run(Parser<0, 0, *S>::parse(), s, pn...);
+				return Parser<stream, 0, Pn...>::run(s, pn...);
 			}
 
 		private:
-			template<typename stream, char...ssn, template<bool, char...> class ParserBuffer, typename ... Pn>
-			static stream & run(const ParserBuffer<false, ssn...> &, stream & s, const Pn & ... pn)
-			{
-				StreamWriter<S, 0, stream, ssn...>::write(s, pn...);
-				return s;
-			}
+			template<typename stream, int pos, typename ... Pn>
+			struct Parser {
+				static inline stream &
+				run(stream & s, const Pn & ... pn)
+				{
+					if (pos != L) {
+						constexpr int ph = strchrnul<S, '%', pos>();
+						if constexpr (ph != pos) {
+							s.write((S + pos), ph - pos);
+						}
+						if constexpr (ph != L) {
+							packAndWrite<ph>(s, pn...);
+						}
+					}
+					return s;
+				}
+				template<int ph, int off = 0, char ... Pck>
+				static inline void packAndWrite(stream & s, const Pn & ... pn)
+				{
+					if constexpr (ph + off == L || sizeof...(Pck) == 32) {
+						StreamWriter<S, L, ph, stream, Pck...>::write(s, pn...);
+					}
+					else if constexpr (ph + off < L) {
+						packAndWrite<ph, off + 1, Pck..., S[ph + off]>(s, pn...);
+					}
+				}
+			};
 	};
-
-	/// @cond
-	template <const char * const & S, int start, typename stream, char ... sn>
-	template<typename ... Pn>
-	void StreamWriter<S, start, stream, sn...>::write(stream & s, const Pn & ... pn)
-	{
-		next(s, Formatter<S>::template Upto<start, 0, sn...>::scan(s, FormatterImpl::Buffer<0>()), pn...);
-	}
-	/// @endcond
 }
 
 #define AdHocFormatterTypedef(name, str, id) \
-- 
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