public static boolean isInt64(BigInteger value) {
        if (FIELD_BIGINTEGER_MAG_OFFSET != -1) {
            int[] mag = (int[]) UNSAFE.getObject(value, FIELD_BIGINTEGER_MAG_OFFSET);
            if (mag.length <= 1) {
                return true;
            }

            if (mag.length == 2) {
                int mag0 = mag[0];
                return mag[0] >= 0 || (mag0 == Integer.MIN_VALUE && mag[1] == 0 && value.signum() == -1);
            }
        }
        return value.compareTo(BIGINT_INT64_MIN) >= 0 && value.compareTo(BIGINT_INT64_MAX) <= 0;
    }
All the positive powers of 10 that can be
represented exactly in double/float.
core/src/main/java/com/alibaba/fastjson2/util/TypeUtils.java