Method parseInt

json/parse.go:83–160

parseInt parses a decimal representation of an int64 from b. The function is equivalent to calling strconv.ParseInt(string(b), 10, 64) but it prevents Go from making a memory allocation for converting a byte slice to a string (escape analysis fails due to the error returned by strconv.ParseInt). B

(b []byte, t reflect.Type)

// Because it only works with base 10 the function is also significantly faster
// than strconv.ParseInt.
func (d decoder) parseInt(b []byte, t reflect.Type) (int64, []byte, error) {
	var value int64
	var count int

	if len(b) == 0 {
		return 0, b, syntaxError(b, "cannot decode integer from an empty input")
	}

	if b[0] == '-' {
		const max = math.MinInt64
		const lim = max / 10

		if len(b) == 1 {
			return 0, b, syntaxError(b, "cannot decode integer from '-'")
		}

		if len(b) > 2 && b[1] == '0' && '0' <= b[2] && b[2] <= '9' {
			return 0, b, syntaxError(b, "invalid leading character '0' in integer")
		}

		for _, c := range b[1:] {
			if c < '0' || c > '9' {
				if count == 0 {
					b, err := d.inputError(b, t)
					return 0, b, err
				}
				break
			}

			if value < lim {
				return 0, b, unmarshalOverflow(b, t)
			}

			value *= 10
			x := int64(c - '0')

			if value < (max + x) {
				return 0, b, unmarshalOverflow(b, t)
			}

			value -= x
			count++
		}

		count++
	} else {
		if len(b) > 1 && b[0] == '0' && '0' <= b[1] && b[1] <= '9' {
			return 0, b, syntaxError(b, "invalid leading character '0' in integer")
		}

		for ; count < len(b) && b[count] >= '0' && b[count] <= '9'; count++ {
			x := int64(b[count] - '0')
			next := value*10 + x
			if next < value {
				return 0, b, unmarshalOverflow(b, t)
			}
			value = next
		}