移位整数时如何绕过Go int64值限制？

Question

I'm trying with Go to get values of KiB, MiB, ..., ZiB, Yib which are respectively KibiByte, MebiByte, ..., ZebiByte, YobiByte.

My code in Golang is:

package main 
import ( 
    "fmt"
)

func main() {
    s := []string{"KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"}

    for k,v := range(s) {
        fmt.Printf("%s: %v
", v, 1 << uint64(10 * (k+1)))
    }
}

But, the values of ZiB and YiB overflows Go uint64 and this why I'm having this output:

KiB: 1024
MiB: 1048576
GiB: 1073741824
TiB: 1099511627776         // exceeds 1 << 32
PiB: 1125899906842624
EiB: 1152921504606846976
ZiB: 0                    // exceeds 1 << 64
YiB: 0                    // exceeds 1 << 64

Otherwise, with the same shifting logic in Python3 within this code:

a = ["KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"]
for k,v in enumerate(a):
    print("{}: {}".format(v, 1 << (10 *(k+1))))

The output is correct, like the output below:

KiB: 1024
MiB: 1048576
GiB: 1073741824
TiB: 1099511627776
PiB: 1125899906842624
EiB: 1152921504606846976
ZiB: 1180591620717411303424
YiB: 1208925819614629174706176

So, how can I bypass Go uint64 limits and get the correct values using shifting integers like what I can get from shifting integers using Python.

Thanks.

Answer 1

You can't work with numbers that require more than 64bits with a primitive uint64. Python has arbitrary precision integers, and to get the same in Go you need to use the math/big package.

s := []string{"KiB", "MiB", "GiB", "TiB", "PiB", "EiB", "ZiB", "YiB"}

one := big.NewInt(1)
for k, v := range s {
    fmt.Printf("%s: %v
", v, new(big.Int).Lsh(one, uint(10*(k+1))))
}

https://play.golang.org/p/i5v5P5QgQb