i'm trying to understand a constant 0x9e3779b9 what kind of data is this? it's not binary, not decimal, what is this?
it's a constant used on the TEA algorithm it says it's derived from the golden number but the golden number is 1.618?
As others have said, the constant is an integer in hexadecimal form. Specifically, it is a 32-bit integer in hexadecimal form. If the constant is a signed integer, then 0x9e3779b9 is negative 1640531527 decimal in two's complement form; therefore, it may be a scaled integer fraction that has been adjusted to deal with non-integral of 2 related problems.
Two's complement negative to positive conversion in hex
or using the 1's complement operator ~ in the C family of languages
Two's complement negative to positive conversion in binary
I think this StackOverflow question answers it:
Essentially, it is a "golden number" for hash functions, and it being an integer is quicker to calculate.