[Golang] Convert size in bytes to Bytes, Kilobytes, Megabytes, GB and TB

gistfile1.txt

package main

import (
  "fmt"
  "math"
  "strconv"
)

var (
	sizeInMB float64 = 999 // This is in megabytes
	suffixes [5]string
)

func Round(val float64, roundOn float64, places int ) (newVal float64) {
	var round float64
	pow := math.Pow(10, float64(places))
	digit := pow * val
	_, div := math.Modf(digit)
	if div >= roundOn {
		round = math.Ceil(digit)
	} else {
		round = math.Floor(digit)
	}
	newVal = round / pow
	return
}

func main() {
	size := sizeInMB * 1024 * 1024 // This is in bytes
	suffixes[0] = "B"
	suffixes[1] = "KB"
	suffixes[2] = "MB"
	suffixes[3] = "GB"
	suffixes[4] = "TB"
	
	base := math.Log(size)/math.Log(1024)
	getSize := Round(math.Pow(1024, base - math.Floor(base)), .5, 2)
	getSuffix := suffixes[int(math.Floor(base))]
	fmt.Println(strconv.FormatFloat(getSize, 'f', -1, 64)+" "+string(getSuffix))
}

@qxxt can you please provide more information about your solution?

(1<<10) is 1024. It is a byte shift operation. 1024 byte is equal to 1 kb.

(1<<20) is also a byte shift operation and is equal to 1024*1024. It's a total byte of 1mb. Byte unit are a base2 number.

1gb is 1mb*1mb, and so on...

@anikitenko
And since binary is base 2.
1<<10 is equal to 2^10.
1<<20 = 2^20.
....

const (
    _ = 1 << (10 * iota)
    KiB
    MiB
    GiB
    TiB
)

KiB = 1_024
MiB = 1_048_576
GiB = 1_073_741_824
TiB = 1_099_511_627_776

const (
_ = iota //ignore first value by assigning to blank identifier
KB = 1 << (10 * iota)
MB
GB
TB
PB
EB
ZB
YB
)

@thisisankit27 thank you but how will these consts help me to determine for example 618761333 bytes are exactly KB, MB, GB? The reason I'm asking is that my mathematical method allows to determine index in array but what about const?

Simpler:

func prettyByteSize(b int) string {
	bf := float64(b)
	for _, unit := range []string{"", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei", "Zi"} {
		if math.Abs(bf) < 1024.0 {
			return fmt.Sprintf("%3.1f%sB", bf, unit)
		}
		bf /= 1024.0
	}
	return fmt.Sprintf("%.1fYiB", bf)
}

Converted from here: https://stackoverflow.com/a/1094933/1333724

@maxmcd thanks 😇