Error while Multiplying a u64 to u128 in Rust? - rust

Question

I want to multiply a u128 number with a u64 number. u64 will always be less than or equal to one. Amount is always greater than 1000000(1 million)
fn testing(amount:u128, starting_time:u64, ending_time:u64, duration:u64){
return amount*((ending_time - starting_time:u64)/duration)
}
Even if the number should return something like 500,000 it always returns zero unless the ((ending_time - starting_time:u64)/duration) equals 1 then the return value always amounts.
I want to give less weightage to someone if they enter the last to the lottery. Both starting and ending times are u64 because they are in UNIX timestamps.
Example: Let's say Alice entered the lottery at time 0. Same time the lottery was started. So Alice would get full weightage for the amount she deposited let's say she deposited 30000 so she will get 30000 tickets.
Bob entered the lottery halfway through the lottery means that whatever he deposits he will get half the weightage of the deposited amount. If he deposits 30000 he will get 15000 tickets.

Answer 1

The best solution I found is:
(amount/1000000) * (( ((end_time - start_time)*1000000 )/duration ) as u128)

Answer 2

I see 2 problems with your code:
You are trying to subtract 2 timestamps, but is that going to leave you with a timestamp? or a number? and if it is the number, is that in seconds or milliseconds or what? and does duration also represent seconds or milliseconds or is it another timestamp?
If all that code still makes sense, then you have a second problem:
Your expression: ending_time - starting_time)/duration, presumably you are expecting it to be a fraction between 0 & 1, right? well if all your variables are ints, then your result is going to be an int, which means guess what? no fraction.
You need to cast all that stuff to floats, or multiply the amount first so you don't have to worry about the fraction. Maybe try this:
return amount*(ending_time - starting_time)/duration;