ircd: Optimize tolower transform.

ircd/stringops.cc

@@ -8,6 +8,8 @@
 // copyright notice and this permission notice is present in all copies. The
 // full license for this software is available in the LICENSE file.
 
+#include <RB_INC_X86INTRIN_H
+
 ircd::string_view
 ircd::toupper(const mutable_buffer &out,
               const string_view &in)
@@ -21,7 +23,7 @@ noexcept
 	const auto end
 	{
 		std::transform(begin(in), stop, begin(out), []
-		(const auto &c)
+		(auto&& c)
 		{
 			return std::toupper(c);
 		})
@@ -34,6 +36,54 @@ noexcept
 	};
 }
 
+#if defined(HAVE_X86INTRIN_H) && defined(__SSE2__)
+ircd::string_view
+ircd::tolower(const mutable_buffer &out,
+              const string_view &in)
+noexcept
+{
+	const __m128i *src_
+	{
+		reinterpret_cast<const __m128i *>(begin(in))
+	};
+
+	__m128i *dst
+	{
+		reinterpret_cast<__m128i *>(begin(out))
+	};
+
+	const auto stop
+	{
+		std::next(begin(in), std::min(size(in), size(out)))
+	};
+
+	while(reinterpret_cast<const char *>(src_) + sizeof(__m128i)  < stop)
+	{
+		const __m128i lit_A1      { _mm_set1_epi8('A' - 1)          };
+		const __m128i lit_Z1      { _mm_set1_epi8('Z' + 1)          };
+		const __m128i addend      { _mm_set1_epi8('a' - 'A')        };
+		const __m128i src         { _mm_loadu_si128(src_++)         };
+		const __m128i gte_A       { _mm_cmpgt_epi8(src, lit_A1)     };
+		const __m128i lte_Z       { _mm_cmplt_epi8(src, lit_Z1)     };
+		const __m128i mask        { _mm_and_si128(gte_A, lte_Z)     };
+		const __m128i ctrl_mask   { _mm_and_si128(mask, addend)     };
+		const __m128i result      { _mm_add_epi8(src, ctrl_mask)    };
+
+		_mm_storeu_si128(dst++, result);
+	}
+
+	const auto end{std::transform
+	(
+		reinterpret_cast<const char *>(src_),
+		stop,
+		reinterpret_cast<char *>(dst),
+		::tolower
+	)};
+
+	assert(intptr_t(begin(out)) <= intptr_t(end));
+	return string_view{begin(out), end};
+}
+#else
 ircd::string_view
 ircd::tolower(const mutable_buffer &out,
               const string_view &in)
@@ -46,11 +96,7 @@ noexcept
 
 	const auto end
 	{
-		std::transform(begin(in), stop, begin(out), []
+		std::transform(begin(in), stop, begin(out), ::tolower)
-		(const auto &c)
-		{
-			return std::tolower(c);
-		})
 	};
 
 	assert(intptr_t(begin(out)) <= intptr_t(end));
@@ -59,6 +105,7 @@ noexcept
 		data(out), size_t(std::distance(begin(out), end))
 	};
 }
+#endif
 
 std::string
 ircd::replace(const string_view &s,