what is the proper way to read architecture limits

Hi
I was trying to determine what is the maximum hashtable length in core, but it did not go so well.The max_table_length is defined as 
let max_table_length = Int_pow2.floor_pow2 Sys.max_array_length
which would indicate the smallest power of two of Sys.max_array_length. At which point would you encounter an int overflow then? These are quite large numbers and we should never encounter them in our programs. Maximum string length has 17 digits and max int has 19 digits. I could not pronounce the Sys.max_array_length number, but it would appear the max hashtable size I estimate to be a quadrillion number. What is the right answer?
Sys.max_array_length returns -: int = 18014398509481938 which would read, of course depending where you are, 180 quadrillion 143 trillion 985 billion 94 million 481 thousand 983. This is a lot bigger still than the Sys.max_string_length -: int = 144115188075855863 that reads 144 quadrillion 115 trillion 188 billion 75 million 855 thousand 863. You are not very likely to encounter a max int or Int64.max_int for that matter.String.length (string_of_int max_int) returns -: int = 19 with max_int of 4611686018427387903. Which would read
4 quintillion (exa) 611 quadrillion (peta) 686 trillion (tera) 18 billion (giga) 427 million (mega) 387 thousand (kilo) 903. A max_int + 1 continues to count upwards, but returns a negative sign indicating an overflow. A max hashtable size would be bigger than max string length but considerably smaller than a max int. Operations on that big of an hashtable would be painfully slow.
With kind regards,
jean