Function ReadVariableWidthInt

utils/binary/read.go:94–119

ReadVariableWidthInt reads and returns an int in Git VLQ special format: Ordinary VLQ has some redundancies, example: the number 358 can be encoded as the 2-octet VLQ 0x8166 or the 3-octet VLQ 0x808166 or the 4-octet VLQ 0x80808166 and so forth. To avoid these redundancies, the VLQ format used in

(r io.Reader)

//         dheader[--pos] = 128 | (--ofs & 127);
//
func ReadVariableWidthInt(r io.Reader) (int64, error) {
	var c byte
	if err := Read(r, &c); err != nil {
		return 0, err
	}

	var v = int64(c & maskLength)
	for c&maskContinue > 0 {
		// Reject input that, after the v++ and shift below, would
		// not fit in an int64. With v < (MaxInt64-127)>>7, the
		// post-increment v is at most (MaxInt64-127)>>7 and the
		// final (v << 7) + (c & 0x7F) stays within int64.
		if v >= (math.MaxInt64-int64(maskLength))>>lengthBits {
			return 0, ErrIntegerOverflow
		}

		v++
		if err := Read(r, &c); err != nil {
			return 0, err
		}

		v = (v << lengthBits) + int64(c&maskLength)
	}

	return v, nil
}

const (
	maskContinue = uint8(128) // 1000 000