Optimized nano seconds formatting

bench/formatter-bench.cpp

@@ -50,8 +50,7 @@ void bench_formatters()
     for(auto &flag:all_flags)
     {
         auto pattern = std::string("%") + flag;
-        benchmark::RegisterBenchmark(pattern.c_str(), bench_formatter, pattern);
-
+        benchmark::RegisterBenchmark(pattern.c_str(), bench_formatter, pattern)->Iterations(2500000);
     }
 
     // complex patterns
@@ -62,7 +61,7 @@ void bench_formatters()
     };
     for(auto &pattern:patterns)
     {
-        benchmark::RegisterBenchmark(pattern.c_str(), bench_formatter, pattern);
+        benchmark::RegisterBenchmark(pattern.c_str(), bench_formatter, pattern)->Iterations(2500000);
     }
 }
 

include/spdlog/details/fmt_helper.h

@@ -110,6 +110,19 @@ inline void pad6(size_t n, fmt::basic_memory_buffer<char, Buffer_Size> &dest)
     pad3(static_cast<int>(n % 1000), dest);
 }
 
+
+template<size_t Buffer_Size>
+inline void pad9(size_t n, fmt::basic_memory_buffer<char, Buffer_Size> &dest)
+{
+    if (n > 99999999)
+    {
+        append_int(n, dest);
+        return;
+    }
+    pad6(static_cast<int>(n / 1000), dest);
+    pad3(static_cast<int>(n % 1000), dest);
+}
+
 // return fraction of a second of the given time_point.
 // e.g.
 // fraction<std::milliseconds>(tp) -> will return the millis part of the second

include/spdlog/details/pattern_formatter.h

@@ -486,7 +486,8 @@ public:
         scoped_pad p(field_size, padinfo_, dest);
 
         auto ns = fmt_helper::time_fraction<std::chrono::nanoseconds>(msg.time);
-        fmt::format_to(dest, "{:09}", ns.count());
+        fmt_helper::pad9(static_cast<size_t>(ns.count()), dest);
+
     }
 };
 

tests/test_fmt_helper.cpp

@@ -22,6 +22,13 @@ void test_pad6(std::size_t n, const char *expected)
     REQUIRE(fmt::to_string(buf) == expected);
 }
 
+void test_pad9(std::size_t n, const char *expected)
+{
+    fmt::memory_buffer buf;
+    spdlog::details::fmt_helper::pad9(n, buf);
+    REQUIRE(fmt::to_string(buf) == expected);
+}
+
 TEST_CASE("pad2", "[fmt_helper]")
 {
     test_pad2(0, "00");
@@ -52,3 +59,19 @@ TEST_CASE("pad6", "[fmt_helper]")
     test_pad6(12345, "012345");
     test_pad6(123456, "123456");
 }
+
+
+TEST_CASE("pad9", "[fmt_helper]")
+{
+    test_pad9(0,"000000000");
+    test_pad9(3, "000000003");
+    test_pad9(23, "000000023");
+    test_pad9(123, "000000123");
+    test_pad9(1234, "000001234");
+    test_pad9(12345, "000012345");
+    test_pad9(123456, "000123456");
+    test_pad9(1234567, "001234567");
+    test_pad9(12345678, "012345678");
+    test_pad9(123456789, "123456789");
+    test_pad9(1234567891, "1234567891");
+}