Function DecodeVarint

decoder.go:991–1025

DecodeVarint reads a base-128 [varint encoded] integer from p and returns the value and the number of bytes that were consumed. [varint encoded]: https://developers.google.com/protocol-buffers/docs/encoding#varints

(p []byte)

//
// [varint encoded]: https://developers.google.com/protocol-buffers/docs/encoding#varints
func DecodeVarint(p []byte) (v uint64, n int, err error) {
	if len(p) == 0 {
		return 0, 0, ErrInvalidVarintData
	}
	// single-byte values don't need any processing
	if p[0] < 0x80 {
		return uint64(p[0]), 1, nil
	}
	// 2-9 byte values
	if len(p) < 10 {
		for shift := uint(0); shift < 64; shift += 7 {
			if n >= len(p) {
				return 0, 0, io.ErrUnexpectedEOF
			}
			b := uint64(p[n])
			n++
			v |= (b & 0x7f << shift)
			if (b & 0x80) == 0 {
				return v, n, nil
			}
		}
		return 0, 0, ErrValueOverflow
	}
	// 10-byte values
	// . we already know the first byte has the high-bit set, so grab it's value then walk bytes 2-10
	v = uint64(p[0] & 0x7f)
	for i, shift := 1, 7; i < 10; i, shift = i+1, shift+7 {
		b := uint64(p[i])
		v |= (b & 0x7f) << shift
		if (b & 0x80) == 0 {
			return v, i + 1, nil
		}
	}
	return 0, 0, ErrValueOverflow
}

// DecodeZigZag32 reads a base-128 [zig zag encoded] 32-bit integer from p and returns the value and the
// number of bytes that were consumed.