decode_int.go

package json

import "unsafe"

type intDecoder struct {
	op func(unsafe.Pointer, int64)
}

func newIntDecoder(op func(unsafe.Pointer, int64)) *intDecoder {
	return &intDecoder{op: op}
}

var (
	pow10i64 = [...]int64{
		1e00, 1e01, 1e02, 1e03, 1e04, 1e05, 1e06, 1e07, 1e08, 1e09,
		1e10, 1e11, 1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18,
	}
)

func (d *intDecoder) parseInt(b []byte) int64 {
	isNegative := false
	if b[0] == '-' {
		b = b[1:]
		isNegative = true
	}
	maxDigit := len(b)
	sum := int64(0)
	for i := 0; i < maxDigit; i++ {
		c := int64(b[i]) - 48
		digitValue := pow10i64[maxDigit-i-1]
		sum += c * digitValue
	}
	if isNegative {
		return -1 * sum
	}
	return sum
}

var (
	numTable = [256]bool{
		'0': true,
		'1': true,
		'2': true,
		'3': true,
		'4': true,
		'5': true,
		'6': true,
		'7': true,
		'8': true,
		'9': true,
	}
)

func (d *intDecoder) decodeStreamByte(s *stream) ([]byte, error) {
	for {
		switch s.char() {
		case ' ', '\n', '\t', '\r':
			s.cursor++
			continue
		case '-':
			start := s.cursor
			for {
				s.cursor++
				if numTable[s.char()] {
					continue
				} else if s.char() == nul {
					if s.read() {
						s.cursor-- // for retry current character
						continue
					}
				}
				break
			}
			num := s.buf[start:s.cursor]
			s.reset()
			if len(num) < 2 {
				goto ERROR
			}
			return num, nil
		case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			start := s.cursor
			for {
				s.cursor++
				if numTable[s.char()] {
					continue
				} else if s.char() == nul {
					if s.read() {
						s.cursor-- // for retry current character
						continue
					}
				}
				break
			}
			num := s.buf[start:s.cursor]
			s.reset()
			return num, nil
		case nul:
			if s.read() {
				continue
			}
			goto ERROR
		default:
			goto ERROR
		}
	}
ERROR:
	return nil, errUnexpectedEndOfJSON("number(integer)", s.totalOffset())
}

func (d *intDecoder) decodeByte(buf []byte, cursor int64) ([]byte, int64, error) {
	for {
		switch buf[cursor] {
		case ' ', '\n', '\t', '\r':
			cursor++
			continue
		case '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
			start := cursor
			cursor++
		LOOP:
			if numTable[buf[cursor]] {
				cursor++
				goto LOOP
			}
			num := buf[start:cursor]
			return num, cursor, nil
		default:
			return nil, 0, errInvalidCharacter(buf[cursor], "number(integer)", cursor)
		}
	}
	return nil, 0, errUnexpectedEndOfJSON("number(integer)", cursor)
}

func (d *intDecoder) decodeStream(s *stream, p unsafe.Pointer) error {
	bytes, err := d.decodeStreamByte(s)
	if err != nil {
		return err
	}
	d.op(p, d.parseInt(bytes))
	return nil
}

func (d *intDecoder) decode(buf []byte, cursor int64, p unsafe.Pointer) (int64, error) {
	bytes, c, err := d.decodeByte(buf, cursor)
	if err != nil {
		return 0, err
	}
	cursor = c
	d.op(p, d.parseInt(bytes))
	return cursor, nil
}