sint64(value) {
        let long = pb_long_1.PbLong.from(value), 
        // zigzag encode
        sign = long.hi >> 31, lo = (long.lo << 1) ^ sign, hi = ((long.hi << 1) | (long.lo >>> 31)) ^ sign;
        goog_varint_1.varint64write(lo, hi, this.buf);
        return this;
    }
Write a `sint64` value, a signed, zig-zag-encoded 64-bit varint.