When it comes to salary payment, normally no two companies uses the same policy, unless stated in Labour Law.
Anyway, here's my experience:
I quit my first job after working there for about a year. I have worked until the 7th of the month (just an example, don't really remember the details), that was including one weekend. It's like I have worked for a week, so I would expect to get about 25% of salary for that month. Anyway, the HR paid me only 5 x (salary/30). I was like WTF?
Then I joined the new company the next day, and at the end of the month, I was paid full monthly salary. The new HR wasn't that calculative to exclude my first week pay because I was not with them yet.
How to calculate partial monthly salary, It is fair?