Optimize %F/%T format/parse (#322)

* add benchmark
* optimize parse %F and %T
* optimize format %F and %T

Author: Roman-Koshelev

src/cctz_benchmark.cc

@@ -400,6 +400,7 @@ const char* const kFormats[] = {
     RFC3339_sec,            // 3
     "%Y-%m-%d%ET%H:%M:%S",  // 4
     "%Y-%m-%d",             // 5
+    "%F%ET%T",              // 6
 };
 const int kNumFormats = sizeof(kFormats) / sizeof(kFormats[0]);
 

src/time_zone_format.cc

@@ -334,7 +334,7 @@ std::string format(const std::string& format, const time_point<seconds>& tp,
   const std::tm tm = ToTM(al);
 
   // Scratch buffer for internal conversions.
-  char buf[3 + kDigits10_64];  // enough for longest conversion
+  char buf[6 + (kDigits10_64 + 2)];  // enough for longest conversion %F
   char* const ep = buf + sizeof(buf);
   char* bp;  // works back from ep
 
@@ -378,7 +378,7 @@ std::string format(const std::string& format, const time_point<seconds>& tp,
     if (cur == end || (cur - percent) % 2 == 0) continue;
 
     // Simple specifiers that we handle ourselves.
-    if (strchr("YmdeUuWwHMSzZs%", *cur)) {
+    if (strchr("YmdeFUuWwHMSTzZs%", *cur)) {
       if (cur - 1 != pending) {
         FormatTM(&result, std::string(pending, cur - 1), tm);
       }
@@ -399,6 +399,14 @@ std::string format(const std::string& format, const time_point<seconds>& tp,
           if (*cur == 'e' && *bp == '0') *bp = ' ';  // for Windows
           result.append(bp, static_cast<std::size_t>(ep - bp));
           break;
+        case 'F':
+          bp = Format02d(ep, al.cs.day());
+          *--bp = '-';
+          bp = Format02d(bp, al.cs.month());
+          *--bp = '-';
+          bp = Format64(bp, 0, al.cs.year());
+          result.append(bp, static_cast<std::size_t>(ep - bp));
+          break;
         case 'U':
           bp = Format02d(ep, ToWeek(civil_day(al.cs), weekday::sunday));
           result.append(bp, static_cast<std::size_t>(ep - bp));
@@ -427,6 +435,14 @@ std::string format(const std::string& format, const time_point<seconds>& tp,
           bp = Format02d(ep, al.cs.second());
           result.append(bp, static_cast<std::size_t>(ep - bp));
           break;
+        case 'T':
+          bp = Format02d(ep, al.cs.second());
+          *--bp = ':';
+          bp = Format02d(bp, al.cs.minute());
+          *--bp = ':';
+          bp = Format02d(bp, al.cs.hour());
+          result.append(bp, static_cast<std::size_t>(ep - bp));
+          break;
         case 'z':
           bp = FormatOffset(ep, al.offset, "");
           result.append(bp, static_cast<std::size_t>(ep - bp));
@@ -764,6 +780,20 @@ bool parse(const std::string& format, const std::string& input,
         data = ParseInt(data, 2, 1, 31, &tm.tm_mday);
         week_num = -1;
         continue;
+      case 'F':
+        data = ParseInt(data, 0, kyearmin, kyearmax, &year);
+        if (data != nullptr) {
+          saw_year = true;
+          data = (*data == '-' ? data + 1 : nullptr);
+        }
+        data = ParseInt(data, 2, 1, 12, &tm.tm_mon);
+        if (data != nullptr) {
+          tm.tm_mon -= 1;
+          data = (*data == '-' ? data + 1 : nullptr);
+        }
+        data = ParseInt(data, 2, 1, 31, &tm.tm_mday);
+        week_num = -1;
+        continue;
       case 'U':
         data = ParseInt(data, 0, 0, 53, &week_num);
         week_start = weekday::sunday;
@@ -789,13 +819,20 @@ bool parse(const std::string& format, const std::string& input,
       case 'S':
         data = ParseInt(data, 2, 0, 60, &tm.tm_sec);
         continue;
+      case 'T':
+        data = ParseInt(data, 2, 0, 23, &tm.tm_hour);
+        twelve_hour = false;
+        data = (data != nullptr && *data == ':' ? data + 1 : nullptr);
+        data = ParseInt(data, 2, 0, 59, &tm.tm_min);
+        data = (data != nullptr && *data == ':' ? data + 1 : nullptr);
+        data = ParseInt(data, 2, 0, 60, &tm.tm_sec);
+        continue;
       case 'I':
       case 'l':
       case 'r':  // probably uses %I
         twelve_hour = true;
         break;
       case 'R':  // uses %H
-      case 'T':  // uses %H
       case 'c':  // probably uses %H
       case 'X':  // probably uses %H
         twelve_hour = false;