How is date encoded/stored in MySQL?-CodePudding

I have to parse date from raw bytes I get from the database for my application on C . I've found out that date in MySQL is 4 bytes and the last two are month and day respectively. But the first two bytes strangely encode the year, so if the date is 2002-08-30, the content will be 210, 15, 8, 31. If the date is 1996-12-22, the date will be stored as 204, 15, 12, 22. Obviously, the first byte can't be bigger than 255, so I've checked year 2047 -- it's 255, 15, and 2048 -- it's 128, 16.

At first I thought that the key is binary operations, but I did not quite understand the logic:

2047: 0111 1111 1111
255:  0000 1111 1111
15:   0000 0000 1111

2048: 1000 0000 0000
128:  0000 1000 0000
16:   0000 0001 0000

Any idea?

CodePudding user response：

It seems that the logic of encoding is to erase the most significant bit of the first number and to write the second number from this erased bit like this:

2002 from 210 and 15:

1101 0010 -> _101 0010;
0000 1111   _101 0010 -> 0111 1101 0010

2048 from 128 and 16:

1000 0000 -> _000 0000
0001 0000   _000 0000 -> 1000 0000 0000

CodePudding user response：

Based on what you provide, it seems to be N1 - 128 N2 * 128.