RegExp: ignore case flag

[vanodevium]

No description provided.

[kolyshkin]

We are getting rid of using regexp in this library; it is faster and smaller that way; see #40

[vanodevium]

@kolyshkin No problem. Good choice!

Maybe next code would be useful...

var units = []byte("kmgtpezy")

func parseString(sizeStr string) (int64, error) {
	sizeStr = strings.ToLower(sizeStr)
	strLen := len(sizeStr)
	if strLen == 0 {
		return -1, fmt.Errorf("invalid size: '%s'", sizeStr)
	}
	var unitPrefixPos, lastNumberPos int
	var binary bool
	for i := strLen - 1; i >= 0; i-- {
		if unicode.IsDigit(rune(sizeStr[i])) {
			lastNumberPos = i
			break
		}

		if sizeStr[i] == 'i' {
			binary = true
			continue
		}

		if sizeStr[i] != ' ' {
			unitPrefixPos = i
		}
	}

	size, err := strconv.ParseFloat(sizeStr[:lastNumberPos+1], 64)
	if err != nil {
		return -1, err
	}

	if size < 0 {
		return -1, fmt.Errorf("size is less than zero")
	}

	if unitPrefixPos > 0 {
		index := bytes.IndexByte(units, sizeStr[unitPrefixPos])
		if index != -1 {
			base := 1000
			if binary {
				base = 1024
			}
			size *= math.Pow(float64(base), float64(index+1))
		}
	}

	return int64(size), nil
}

This code can parse human readable string, but looks only for valid suffix.
The main goal is that it not used map with unit and multiplier, only simple math :)