Agree with dxw00d,
look at the parsing of the string:
d=4 ==> is the default duration.
b=100 => beats per minute, it defines :
wholenote = (60 * 1000L / bpm) * 4; // this is the time for whole note (in milliseconds)
finally the 16e6 is split in 16 and e6, giving a duration of :
if(num) duration = wholenote / num;
else duration = wholenote / default_dur;