src/main/java/io/reactivex/internal/util/BackpressureHelper.java
public static long addCap(long a, long b) {
        long u = a + b;
        if (u < 0L) {
            return Long.MAX_VALUE;
        }
        return u;
    }
public static long addCap(long a, long b) {
        long u = a + b;
        if (u < 0L) {
            return Long.MAX_VALUE;
        }
        return u;
    }
Adds two long values and caps the sum at Long.MAX_VALUE.
@param a the first value
@param b the second value
@return the sum capped at Long.MAX_VALUE