Go: Convert IP to CIDR

Golang-IP-to-CIDR

/ Convert IPv4 range into CIDR
func iPv4RangeToCIDRRange(ipStart string, ipEnd string) (cidrs []string, err error) {

	cidr2mask := []uint32{
		0x00000000, 0x80000000, 0xC0000000,
		0xE0000000, 0xF0000000, 0xF8000000,
		0xFC000000, 0xFE000000, 0xFF000000,
		0xFF800000, 0xFFC00000, 0xFFE00000,
		0xFFF00000, 0xFFF80000, 0xFFFC0000,
		0xFFFE0000, 0xFFFF0000, 0xFFFF8000,
		0xFFFFC000, 0xFFFFE000, 0xFFFFF000,
		0xFFFFF800, 0xFFFFFC00, 0xFFFFFE00,
		0xFFFFFF00, 0xFFFFFF80, 0xFFFFFFC0,
		0xFFFFFFE0, 0xFFFFFFF0, 0xFFFFFFF8,
		0xFFFFFFFC, 0xFFFFFFFE, 0xFFFFFFFF,
	}

	ipStartUint32 := iPv4ToUint32(ipStart)
	ipEndUint32 := iPv4ToUint32(ipEnd)

	if ipStartUint32 > ipEndUint32 {
		log.Fatalf("start IP:%s must be less than end IP:%s", ipStart, ipEnd)
	}

	for ipEndUint32 >= ipStartUint32 {
		maxSize := 32
		for maxSize > 0 {

			maskedBase := ipStartUint32 & cidr2mask[maxSize - 1]

			if maskedBase != ipStartUint32 {
				break
			}
			maxSize--

		}

		x := math.Log(float64(ipEndUint32 - ipStartUint32 + 1)) / math.Log(2)
		maxDiff := 32 - int(math.Floor(x))
		if maxSize < maxDiff {
			maxSize = maxDiff
		}

		cidrs = append(cidrs,  uInt32ToIPv4(ipStartUint32) + "/" +  strconv.Itoa(maxSize))

		ipStartUint32 += uint32(math.Exp2(float64(32 - maxSize)))
	}

	return cidrs, err
}

//Convert IPv4 to uint32
func iPv4ToUint32(iPv4 string ) uint32 {

	ipOctets := [4]uint64{}

	for i, v := range strings.SplitN(iPv4,".", 4) {
		ipOctets[i], _  = strconv.ParseUint(v, 10, 32)
	}

	result := (ipOctets[0] << 24) | (ipOctets[1] << 16) | (ipOctets[2] << 8) | ipOctets[3]

	return uint32(result)
}

//Convert uint32 to IP
func uInt32ToIPv4(iPuInt32 uint32) (iP string) {
	iP =  fmt.Sprintf ("%d.%d.%d.%d",
		iPuInt32 >> 24,
		(iPuInt32 & 0x00FFFFFF)>> 16,
		(iPuInt32 & 0x0000FFFF) >> 8,
		iPuInt32 & 0x000000FF)
	return iP
}