By calling atof() on p, we're converting the entire time string (101520.123 for 10:15:20am and 123 milliseconds) to a float, then multiplying by 1000 to get ms. This results in a value that overflows and exhibits all sorts of strange behavior as seconds and minutes turn over. It's clearly not what was intended. From the if statement wrapping the conversion, it is clear that the author intended to make the atof() conversion on the dec pointer, instead. Making this change actually does fix the parsing so that Adafruit_GPS' milliseconds property correctly matches the value in the NMEA sentence.
You guys do great work. Thanks for everything!
move other parsing functions in NMEA_parse.cpp
fix parseTime to be insensitive to number of decimal places and return bool.
add isEmpty() checks where needed.
reorder some declarations.
Ron Barry
Matt Goodrich
Owen Torres
Rick Sellens