Details: http://0x80.pl/notesen.html#note-2013-5
$ make
Sample output:
$ ./test 0 12 5671245 -143433 334535 4543985349054 999999999999999999999 printf => 0.000000 FBSTP => 0 printf => 12.000000 FBSTP => 12 printf => 5671245.000000 FBSTP => 5671245 printf => -143433.000000 FBSTP => -143433 printf => 334535.000000 FBSTP => 334535 printf => 4543985349054.000000 FBSTP => 4543985349054 printf => 10000000000000000000000.000000 FBSTP => NaN/overflow
$ ./speed fbstp... ... 2.285 s simple itoa... ... 0.589 s
$ ./speed.exe FBSTP... ... 1.682 s simple itoa... ... 0.223 s
$ ./speed FBSTP... ... 2.165 s simple itoa... ... 0.419 s