I dont understand your question, can you explain in more detail?
Discussion
I mean from the 1st 50×900×4years?and so on,now its 6.25 then it will be 3.14?Are all these Bitcoin being mined and sold?
Yes, most of them are sold by the miners.
Most of them?okay,what about the rest?aren't there any left overs or something?and what had caused to speed up the date?
The miners get the #bitcoin they mine. So every block, there is generated 6.25 new coins, given to the miner (miners, because they often mine together in pools).
The miners have costs on their operations, so to pay their bills, they often sell their coins.
So those miners who do not sell, they hold their coins.
The halving is set to be every 210.000th block. On average the block time (time to create a new block) is 10 minutes. But as the total hash rate goes up and down, the block time can vary.
At the time i wrote this post, there had been 10 blocks the last hour. With that speed the halving date would come earlier.
Smart AF, satoshi fixed this with a difficulty adjustment.
So every 2016th block, the difficulty of creating a block adjusts based on the hashrate.