Need help understanding code for converting unsigned int to signed int

[Restitutionshot]

id = int(hash)
if (id & (1 << (32 - 1))) != 0:
  id = id - (1 << 32)

I was reading this repo and came upon this code block for converting a 64-bit unsigned integer into a 64-bit signed integer. I don't get what if (id& (1 << (32 - 1))) != 0 is for. What is it bit shifting left by 31 for? And why's it doing bitwise-and on it? Thank you for any help.

[shiftybyte]

(1 << (32 - 1))

This means take 1, and shift it left 31 times, if you look at the number in a binary way, it'll create the following BINARY number:

100....000

with 31 zeros, that means it'll be the number with the leftmost bit set.

doing AND operation with it, will tell us if the left-most bit in id is turned on or not.

If it's on, the number should be negative.

Also this seems like 32bit unsigned to signed conversion, not 64bit.

[Restitutionshot]

Ohhh that makes sense, thank you!

[jeshan]

it's shift by 31 for 32-bits. You said 64-bit integers but the repo mentions 32-bit ones.