diff --git a/sprout/cstring/memchr.hpp b/sprout/cstring/memchr.hpp
index b93abc89..de47093c 100644
--- a/sprout/cstring/memchr.hpp
+++ b/sprout/cstring/memchr.hpp
@@ -3,30 +3,49 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
 	namespace detail {
-		inline SPROUT_CONSTEXPR void const*
-		memchr_impl(unsigned char const* s, unsigned char c, std::size_t n) {
-			return !n ? 0
-				: *s == c ? s
-				: sprout::detail::memchr_impl(s + 1, c, n - 1)
-			;
+		inline SPROUT_CONSTEXPR unsigned char const*
+		memchr_impl(unsigned char const* found, unsigned char const* last) {
+			return found == last ? nullptr
+				: found
+				;
+		}
+		inline SPROUT_CONSTEXPR unsigned char*
+		memchr_impl(unsigned char* found, unsigned char* last) {
+			return found == last ? nullptr
+				: found
+				;
 		}
 	}	// namespace detail
 
 	// 7.21.5.1  memchr 関数
 	inline SPROUT_CONSTEXPR void const*
-	memchr(void const* s, int c, size_t n) {
-		return sprout::detail::memchr_impl(static_cast<unsigned char const*>(s), static_cast<unsigned char>(c), n);
+	memchr(void const* s, int c, std::size_t n) {
+		return sprout::detail::memchr_impl(
+			sprout::as_iterator_base(
+				NS_SSCRISK_CEL_OR_SPROUT::find(
+					sprout::as_iterator(static_cast<unsigned char const*>(s)), sprout::as_iterator(static_cast<unsigned char const*>(s), n),
+					static_cast<unsigned char>(c)
+					)
+				),
+			static_cast<unsigned char const*>(s) + n
+			);
 	}
 
 	inline SPROUT_CONSTEXPR void*
-	memchr(void* s, int c, size_t n) {
-		return const_cast<void*>(
-			sprout::detail::memchr_impl(static_cast<unsigned char*>(s), static_cast<unsigned char>(c), n)
+	memchr(void* s, int c, std::size_t n) {
+		return sprout::detail::memchr_impl(
+			sprout::as_iterator_base(
+				NS_SSCRISK_CEL_OR_SPROUT::find(
+					sprout::as_iterator(static_cast<unsigned char*>(s)), sprout::as_iterator(static_cast<unsigned char*>(s), n),
+					static_cast<unsigned char>(c)
+					)
+				),
+			static_cast<unsigned char*>(s) + n
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/cstring/memcmp.hpp b/sprout/cstring/memcmp.hpp
index 5370b38d..2ad44770 100644
--- a/sprout/cstring/memcmp.hpp
+++ b/sprout/cstring/memcmp.hpp
@@ -3,27 +3,16 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include <sprout/algorithm/tristate_lexicographical_compare.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR int
-		memcmp_impl(unsigned char const* s1, unsigned char const* s2, std::size_t n) {
-			return !n ? 0
-				: *s1 == *s2 ? sprout::detail::memcmp_impl(s1 + 1, s2 + 1, n - 1)
-				: *s1 - *s2
-				;
-		}
-	}	// namespace detail
-
 	// 7.21.4.1  memcmp 関数
 	inline SPROUT_CONSTEXPR int
 	memcmp(void const* s1, void const* s2, std::size_t n) {
-		return sprout::detail::memcmp_impl(
-			static_cast<unsigned char const*>(s1),
-			static_cast<unsigned char const*>(s2),
-			n
+		return sprout::tristate_lexicographical_compare(
+			sprout::as_iterator(static_cast<unsigned char const*>(s1)), sprout::as_iterator(static_cast<unsigned char const*>(s1), n),
+			sprout::as_iterator(static_cast<unsigned char const*>(s2)), sprout::as_iterator(static_cast<unsigned char const*>(s2), n)
 			);
 	}
 }	// namespace sprout
diff --git a/sprout/cstring/strcspn.hpp b/sprout/cstring/strcspn.hpp
index 49d5e2e8..cbb620b2 100644
--- a/sprout/cstring/strcspn.hpp
+++ b/sprout/cstring/strcspn.hpp
@@ -6,21 +6,12 @@
 #include <sprout/cstring/strchr.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR std::size_t
-		strcspn_impl(char const* s1, char const* s2, std::size_t n) {
-			return !*s1 || sprout::strchr(s2, *s1) ? n
-				: sprout::detail::strcspn_impl(s1 + 1, s2, n + 1)
-				;
-		}
-	}	// amespace detail
-
 	// 7.21.5.3  strcspn 関数
 	inline SPROUT_CONSTEXPR std::size_t
 	strcspn(char const* s1, char const* s2) {
-		return sprout::detail::strcspn_impl(s1, s2, 0);
+		return !*s1 || sprout::strchr(s2, *s1) ? 0
+			: 1 + sprout::strcspn(s1 + 1, s2)
+			;
 	}
 }	// namespace sprout
 
diff --git a/sprout/cstring/strlen.hpp b/sprout/cstring/strlen.hpp
index 44809ff9..029ca42f 100644
--- a/sprout/cstring/strlen.hpp
+++ b/sprout/cstring/strlen.hpp
@@ -3,6 +3,9 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
+#include HDR_ITERATOR_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
 	// 7.21.6.3  strlen 関数
@@ -12,6 +15,14 @@ namespace sprout {
 			: 1 + sprout::strlen(s + 1)
 			;
 	}
+
+	inline SPROUT_CONSTEXPR std::size_t
+	strlen(char const* s, std::size_t n) {
+		return NS_SSCRISK_CEL_OR_SPROUT::distance(
+			sprout::as_iterator(s),
+			NS_SSCRISK_CEL_OR_SPROUT::find(sprout::as_iterator(s), sprout::as_iterator(s, n), '\0')
+			);
+	}
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_CSTRING_STRLEN_HPP
diff --git a/sprout/cstring/strncmp.hpp b/sprout/cstring/strncmp.hpp
index d0db0c9d..56bac73a 100644
--- a/sprout/cstring/strncmp.hpp
+++ b/sprout/cstring/strncmp.hpp
@@ -3,19 +3,19 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include <sprout/algorithm/tristate_lexicographical_compare.hpp>
+#include <sprout/cstring/strlen.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
 	// 7.21.4.4  strncmp 関数
 	inline SPROUT_CONSTEXPR int
 	strncmp(char const* s1, char const* s2, std::size_t n) {
-		return !n || (!*s1 && !*s2) ? 0
-			: !*s1 ? -1
-			: !*s2 ? 1
-			: *s1 == *s2 ? sprout::strncmp(s1 + 1, s2 + 1, n - 1)
-			: static_cast<unsigned char>(*s1) - static_cast<unsigned char>(*s2)
-			;
+		return sprout::tristate_lexicographical_compare(
+			sprout::as_iterator(s1), sprout::as_iterator(s1, sprout::strlen(s1, n)),
+			sprout::as_iterator(s2), sprout::as_iterator(s2, sprout::strlen(s2, n))
+			);
 	}
 }	// namespace sprout
 
diff --git a/sprout/cstring/strspn.hpp b/sprout/cstring/strspn.hpp
index 0ffb2cdb..ab2a061b 100644
--- a/sprout/cstring/strspn.hpp
+++ b/sprout/cstring/strspn.hpp
@@ -1,27 +1,18 @@
 #ifndef SPROUT_CSTRING_STRSPN_HPP
-#define SPROUT_CSTRING_XXX_HPP
+#define SPROUT_CSTRING_STRSPN_HPP
 
 #include <cstddef>
 #include <sprout/config.hpp>
 #include <sprout/cstring/strchr.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR std::size_t
-		strspn_impl(char const* s1, char const* s2, std::size_t n) {
-			return !*s1 || !sprout::strchr(s2, *s1) ? n
-				: sprout::detail::strspn_impl(s1 + 1, s2, n + 1)
-				;
-		}
-	}	// namespace detail
-
 	// 7.21.5.6  strspn 関数
 	inline SPROUT_CONSTEXPR std::size_t
 	strspn(char const* s1, char const* s2) {
-		return sprout::detail::strspn_impl(s1, s2, 0);
+		return !*s1 || !sprout::strchr(s2, *s1) ? 0
+			: 1 + sprout::strspn(s1 + 1, s2)
+			;
 	}
 }	// namespace sprout
 
-#endif	// #ifndef SPROUT_CSTRING_XXX_HPP
+#endif	// #ifndef SPROUT_CSTRING_STRSPN_HPP
diff --git a/sprout/cwchar/wcscmp.hpp b/sprout/cwchar/wcscmp.hpp
index 0f6b5521..96baded0 100644
--- a/sprout/cwchar/wcscmp.hpp
+++ b/sprout/cwchar/wcscmp.hpp
@@ -6,6 +6,9 @@
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
+	//
+	// wcscmp
+	//
 	inline SPROUT_CONSTEXPR int
 	wcscmp(wchar_t const* s1, wchar_t const* s2) {
 		return !*s1 && !*s2 ? 0
diff --git a/sprout/cwchar/wcscoll.hpp b/sprout/cwchar/wcscoll.hpp
index 03ce6821..45b6f338 100644
--- a/sprout/cwchar/wcscoll.hpp
+++ b/sprout/cwchar/wcscoll.hpp
@@ -2,11 +2,14 @@
 #define SPROUT_CWCHAR_WCSCOLL_HPP
 
 #include <sprout/config.hpp>
-#include <sprout/cstring/strcmp.hpp>
+#include <sprout/cwchar/wcscmp.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
+	//
+	// wcscoll
+	//
 	inline SPROUT_CONSTEXPR int
 	wcscoll(wchar_t const* s1, wchar_t const* s2) {
 		return sprout::wcscmp(s1, s2);
diff --git a/sprout/cwchar/wcscspn.hpp b/sprout/cwchar/wcscspn.hpp
index f2a4a0ba..fe68b86e 100644
--- a/sprout/cwchar/wcscspn.hpp
+++ b/sprout/cwchar/wcscspn.hpp
@@ -3,23 +3,17 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
-#include <sprout/cstring/strchr.hpp>
+#include <sprout/cwchar/wcschr.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR std::size_t
-		wcscspn_impl(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
-			return !*s1 || sprout::wcschr(s2, *s1) ? n
-				: sprout::detail::wcscspn_impl(s1 + 1, s2, n + 1)
-				;
-		}
-	}	// amespace detail
-
+	//
+	// wcscspn
+	//
 	inline SPROUT_CONSTEXPR std::size_t
 	wcscspn(wchar_t const* s1, wchar_t const* s2) {
-		return sprout::detail::wcscspn_impl(s1, s2, 0);
+		return !*s1 || sprout::wcschr(s2, *s1) ? 0
+			: 1 + sprout::wcscspn(s1 + 1, s2)
+			;
 	}
 }	// namespace sprout
 
diff --git a/sprout/cwchar/wcslen.hpp b/sprout/cwchar/wcslen.hpp
index b901a4c7..0271e579 100644
--- a/sprout/cwchar/wcslen.hpp
+++ b/sprout/cwchar/wcslen.hpp
@@ -3,14 +3,28 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
+#include HDR_ITERATOR_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
+	//
+	// wcslen
+	//
 	inline SPROUT_CONSTEXPR std::size_t
 	wcslen(wchar_t const* s) {
 		return !*s ? 0
 			: 1 + sprout::wcslen(s + 1)
 			;
 	}
+
+	inline SPROUT_CONSTEXPR std::size_t
+	wcslen(wchar_t const* s, std::size_t n) {
+		return NS_SSCRISK_CEL_OR_SPROUT::distance(
+			sprout::as_iterator(s),
+			NS_SSCRISK_CEL_OR_SPROUT::find(sprout::as_iterator(s), sprout::as_iterator(s, n), L'\0')
+			);
+	}
 }	// namespace sprout
 
 #endif	// #ifndef SPROUT_CWCHAR_WCSLEN_HPP
diff --git a/sprout/cwchar/wcsncmp.hpp b/sprout/cwchar/wcsncmp.hpp
index 77b0c44e..ecf7c083 100644
--- a/sprout/cwchar/wcsncmp.hpp
+++ b/sprout/cwchar/wcsncmp.hpp
@@ -3,18 +3,21 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include <sprout/algorithm/tristate_lexicographical_compare.hpp>
+#include <sprout/cwchar/wcslen.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
+	//
+	// wcsncmp
+	//
 	inline SPROUT_CONSTEXPR int
 	wcsncmp(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
-		return !n || (!*s1 && !*s2) ? 0
-			: !*s1 ? -1
-			: !*s2 ? 1
-			: *s1 == *s2 ? sprout::wcsncmp(s1 + 1, s2 + 1, n - 1)
-			: *s1 - *s2
-			;
+		return sprout::tristate_lexicographical_compare(
+			sprout::as_iterator(s1), sprout::as_iterator(s1, sprout::wcslen(s1, n)),
+			sprout::as_iterator(s2), sprout::as_iterator(s2, sprout::wcslen(s2, n))
+			);
 	}
 }	// namespace sprout
 
diff --git a/sprout/cwchar/wcspbrk.hpp b/sprout/cwchar/wcspbrk.hpp
index 1921fa77..6ac95b1a 100644
--- a/sprout/cwchar/wcspbrk.hpp
+++ b/sprout/cwchar/wcspbrk.hpp
@@ -3,11 +3,14 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
-#include <sprout/cstring/strchr.hpp>
+#include <sprout/cwchar/wcschr.hpp>
 
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
+	//
+	// wcspbrk
+	//
 	inline SPROUT_CONSTEXPR wchar_t const*
 	wcspbrk(wchar_t const* s1, wchar_t const* s2) {
 		return !*s1 ? nullptr
diff --git a/sprout/cwchar/wcsrchr.hpp b/sprout/cwchar/wcsrchr.hpp
index d750af79..e5561e5f 100644
--- a/sprout/cwchar/wcsrchr.hpp
+++ b/sprout/cwchar/wcsrchr.hpp
@@ -7,6 +7,9 @@
 namespace sprout {
 	// Copyright (C) 2011 RiSK (sscrisk)
 
+	//
+	// wcsrchr
+	//
 	inline SPROUT_CONSTEXPR wchar_t const*
 	wcsrchr(wchar_t const* s, int c) {
 		return *s == static_cast<wchar_t>(c) && (!*s || !sprout::wcsrchr(s + 1, c))? s
diff --git a/sprout/cwchar/wcsspn.hpp b/sprout/cwchar/wcsspn.hpp
index f43bf342..a636e3d0 100644
--- a/sprout/cwchar/wcsspn.hpp
+++ b/sprout/cwchar/wcsspn.hpp
@@ -1,26 +1,20 @@
 #ifndef SPROUT_CWCHAR_WCSSPN_HPP
-#define SPROUT_CWCHAR_XXX_HPP
+#define SPROUT_CWCHAR_WCSSPN_HPP
 
 #include <cstddef>
 #include <sprout/config.hpp>
-#include <sprout/cstring/strchr.hpp>
+#include <sprout/cwchar/wcschr.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR std::size_t
-		wcsspn_impl(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
-			return !*s1 || !sprout::wcschr(s2, *s1) ? n
-				: sprout::detail::wcsspn_impl(s1 + 1, s2, n + 1)
-				;
-		}
-	}	// namespace detail
-
+	//
+	// wcsspn
+	//
 	inline SPROUT_CONSTEXPR std::size_t
 	wcsspn(wchar_t const* s1, wchar_t const* s2) {
-		return sprout::detail::wcsspn_impl(s1, s2, 0);
+		return !*s1 || !sprout::wcschr(s2, *s1) ? 0
+			: 1 + sprout::wcsspn(s1 + 1, s2)
+			;
 	}
 }	// namespace sprout
 
-#endif	// #ifndef SPROUT_CWCHAR_XXX_HPP
+#endif	// #ifndef SPROUT_CWCHAR_WCSSPN_HPP
diff --git a/sprout/cwchar/wmemchr.hpp b/sprout/cwchar/wmemchr.hpp
index e4b92b00..e77638bd 100644
--- a/sprout/cwchar/wmemchr.hpp
+++ b/sprout/cwchar/wmemchr.hpp
@@ -3,28 +3,52 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include HDR_ALGORITHM_SSCRISK_CEL_OR_SPROUT
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
 	namespace detail {
 		inline SPROUT_CONSTEXPR wchar_t const*
-		wmemchr_impl(wchar_t const* s, wchar_t c, std::size_t n) {
-			return !n ? 0
-				: *s == c ? s
-				: sprout::detail::wmemchr_impl(s + 1, c, n - 1)
-			;
+		wmemchr_impl(wchar_t const* found, wchar_t const* last) {
+			return found == last ? nullptr
+				: found
+				;
+		}
+		inline SPROUT_CONSTEXPR wchar_t*
+		wmemchr_impl(wchar_t* found, wchar_t* last) {
+			return found == last ? nullptr
+				: found
+				;
 		}
 	}	// namespace detail
 
+	//
+	// wmemchr
+	//
 	inline SPROUT_CONSTEXPR wchar_t const*
 	wmemchr(wchar_t const* s, wchar_t c, size_t n) {
-		return sprout::detail::wmemchr_impl(s, c, n);
+		return sprout::detail::wmemchr_impl(
+			sprout::as_iterator_base(
+				NS_SSCRISK_CEL_OR_SPROUT::find(
+					sprout::as_iterator(s), sprout::as_iterator(s, n),
+					c
+					)
+				),
+			s + n
+			);
 	}
 
 	inline SPROUT_CONSTEXPR wchar_t*
 	wmemchr(wchar_t* s, wchar_t c, size_t n) {
-		return const_cast<wchar_t*>(sprout::detail::wmemchr_impl(s, c, n));
+		return sprout::detail::wmemchr_impl(
+			sprout::as_iterator_base(
+				NS_SSCRISK_CEL_OR_SPROUT::find(
+					sprout::as_iterator(s), sprout::as_iterator(s, n),
+					c
+					)
+				),
+			s + n
+			);
 	}
 }	// namespace sprout
 
diff --git a/sprout/cwchar/wmemcmp.hpp b/sprout/cwchar/wmemcmp.hpp
index 003061f8..650555e2 100644
--- a/sprout/cwchar/wmemcmp.hpp
+++ b/sprout/cwchar/wmemcmp.hpp
@@ -3,23 +3,19 @@
 
 #include <cstddef>
 #include <sprout/config.hpp>
+#include <sprout/iterator/ptr_index_iterator.hpp>
+#include <sprout/algorithm/tristate_lexicographical_compare.hpp>
 
 namespace sprout {
-	// Copyright (C) 2011 RiSK (sscrisk)
-
-	namespace detail {
-		inline SPROUT_CONSTEXPR int
-		wmemcmp_impl(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
-			return !n ? 0
-				: *s1 == *s2 ? sprout::detail::wmemcmp_impl(s1 + 1, s2 + 1, n - 1)
-				: *s1 - *s2
-				;
-		}
-	}	// namespace detail
-
+	//
+	// wmemcmp
+	//
 	inline SPROUT_CONSTEXPR int
 	wmemcmp(wchar_t const* s1, wchar_t const* s2, std::size_t n) {
-		return sprout::detail::wmemcmp_impl(s1, s2, n);
+		return sprout::tristate_lexicographical_compare(
+			sprout::as_iterator(s1), sprout::as_iterator(s1, n),
+			sprout::as_iterator(s2), sprout::as_iterator(s2, n)
+			);
 	}
 }	// namespace sprout
 
diff --git a/sprout/string/char_traits.hpp b/sprout/string/char_traits.hpp
index 7de7a07c..46798a23 100644
--- a/sprout/string/char_traits.hpp
+++ b/sprout/string/char_traits.hpp
@@ -44,6 +44,13 @@ namespace sprout {
 				: found
 				;
 		}
+		template<typename Iterator>
+		static SPROUT_CONSTEXPR std::size_t len(Iterator s, std::size_t n) {
+			return NS_SSCRISK_CEL_OR_SPROUT::distance(
+				s,
+				NS_SSCRISK_CEL_OR_SPROUT::find(s, s + n, char_type())
+				);
+		}
 	public:
 		static void assign(char_type& c1, char_type const& c2) SPROUT_NOEXCEPT {
 			impl_type::assign(c1, c2);
@@ -56,8 +63,8 @@ namespace sprout {
 		}
 		static SPROUT_CONSTEXPR int compare(char_type const* s1, char_type const* s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
-				sprout::as_iterator(s1), sprout::as_iterator(s1, n),
-				sprout::as_iterator(s2), sprout::as_iterator(s2, n),
+				sprout::as_iterator(s1), sprout::as_iterator(s1, len(sprout::as_iterator(s1), n)),
+				sprout::as_iterator(s2), sprout::as_iterator(s2, len(sprout::as_iterator(s2), n)),
 				lt_()
 				);
 		}
@@ -105,7 +112,7 @@ namespace sprout {
 		template<typename ConstIterator>
 		static SPROUT_CONSTEXPR int compare(char_type const* s1, ConstIterator s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
-				sprout::as_iterator(s1), sprout::as_iterator(s1, n),
+				sprout::as_iterator(s1), sprout::as_iterator(s1, len(sprout::as_iterator(s1), n)),
 				s2, s2 + n,
 				lt_()
 				);
@@ -114,7 +121,7 @@ namespace sprout {
 		static SPROUT_CONSTEXPR int compare(ConstIterator s1, char_type const* s2, std::size_t n) {
 			return sprout::tristate_lexicographical_compare(
 				s1, s1 + n,
-				sprout::as_iterator(s2), sprout::as_iterator(s2, n),
+				sprout::as_iterator(s2), sprout::as_iterator(s2, len(sprout::as_iterator(s2), n)),
 				lt_()
 				);
 		}