I'm pulling in data that is in long hexadecimal string form which I need to convert into decimal notation, truncate 18 decimal places, and then serve up in JSON.
For example I may have the hex string:
"0x00000000000000000000000000000000000000000000d3c21bcecceda1000000"
At first I was attempting to use ParseUint(), however since the highest it supports is int64, my number ends up being way too big.
This example after conversion and truncation results in 10^6. However there are instances where this number can be up to 10^12 (meaning pre truncation 10^30!).
What is the best strategy to attack this?
Use math/big for working with numbers larger than 64 bits.
From the Int.SetString example:
s := "d3c21bcecceda1000000"
i := new(big.Int)
i.SetString(s, 16)
fmt.Println(i)
https://play.golang.org/p/vf31ce93vA
The math/big types also support the encoding.TextMarshaler and fmt.Scanner interfaces.
For example
i := new(big.Int)
fmt.Sscan("0x000000d3c21bcecceda1000000", i)
Or
i := new(big.Int)
fmt.Sscanf("0x000000d3c21bcecceda1000000", "0x%x", i)