masaori335 commented on code in PR #12592:
URL: https://github.com/apache/trafficserver/pull/12592#discussion_r2450012593
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src/proxy/hdrs/MIME.cc:
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@@ -51,17 +53,58 @@ using swoc::TextView;
* C O N S T A N T S *
* *
***********************************************************************/
-static DFA *day_names_dfa = nullptr;
-static DFA *month_names_dfa = nullptr;
-static constexpr const char *day_names[] = {
+static constexpr std::array<std::string_view, 7> day_names = {
"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat",
};
-static constexpr const char *month_names[] = {
+static constexpr std::array<std::string_view, 12> month_names = {
"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov",
"Dec",
};
+template <size_t count>
+static consteval std::array<uint32_t, count>
+make_packed(const std::array<std::string_view, count> &names)
+{
+ std::array<uint32_t, count> packed{};
+
+ auto tl = [](char c) -> char { return (c >= 'A' && c <= 'Z') ? (c + 32) : c;
};
+
+ for (size_t i = 0; i < count; ++i) {
+ const auto &sv = names[i];
+ const uint32_t c0 = tl(static_cast<unsigned char>(sv[0]));
+ const uint32_t c1 = tl(static_cast<unsigned char>(sv[1]));
+ const uint32_t c2 = tl(static_cast<unsigned char>(sv[2]));
+ packed[i] = (c0 << 16) | (c1 << 8) | c2;
+ }
+ return packed;
+}
+
+static constexpr std::array<uint32_t, day_names.size()> day_names_packed =
make_packed(day_names);
+static constexpr std::array<uint32_t, month_names.size()> month_names_packed =
make_packed(month_names);
+
+// Case-insensitive match of first 3 characters of input string against array
of names
+// Longer strings will match if their first 3 characters match - this is
intentional for
+// matching non-standard day/month names like "Thursday" or "September".
+template <size_t count>
+__attribute__((always_inline)) static constexpr int
+match_3char_ci(const std::string_view s, const std::array<uint32_t, count>
&names_packed)
+{
+ if (s.size() < 3) {
+ return -1;
+ }
+
+ auto tl = [](char c) -> char { return (c >= 'A' && c <= 'Z') ?
(c + 32) : c; };
+ const uint32_t packed = (tl(s[0]) << 16) | (tl(s[1]) << 8) | tl(s[2]);
+
+ for (size_t i = 0; i < count; i++) {
Review Comment:
It's pretty interesting this liner search is the fastest. I thought
switching this packed string is faster than for loop. Probably, target vector
is short enough.
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