FILETIME to JET_coltypDateTime conversion in ESENT

According to msdn,

FILETIME represents the number of 100-nanoseconds since 1601:

"Holds an unsigned 64-bit date and time value for a file. This value represents the number of 100-nanosecond units since the start of January 1, 1601."

yet the JET_coltypDateTime for DateTime column in Jet database is:

"A double-precision (8-byte) floating point number that represents a date in fractional days since the year 1900. This column type is identical to the variant date type."

I can't seem to find a function to convert FILETIME to JET_coltypDateTime. Also, If I want to do it myself, I cannot seem to find an explanation of how the double represents the time (which bits represent days ...etc)?

MSDN sources http://ift.tt/1DL86SO http://ift.tt/1DeTIzx