How big can a 64bit signed integer be?

Question

In redis,

The range of values supported by HINCRBY is limited to 64 bit signed integers.

And I'd like to know how big can that 64 bit signed integer be.

Answer 1

This article is good for more information about this topic: http://en.wikipedia.org/wiki/Integer_(computer_science)

So the answer to the question should be: From -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807, or from −(2^63) to 2^63 − 1

The highest positive number stored in a signed int is represented binary as

----- 63 ones -----

0111111111111111111111111111111111111111111111111111111111111111 

If you think carefully you can find out that this number is exactly 2^63 - 1.

Answer 2

A signed integer ranges from size −2^(n−1) through 2^(n−1) − 1 so in this case the maximum value would be 2 ^ 63 - 1 or 9,223,372,036,854,775,807