java语言——如何判断整数溢出-白红宇

java语言——如何判断整数溢出

阅读量：339 次

发布时间：2019-03-04

本文共 1520 字，大约阅读时间需要 5 分钟。

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public static int addExact(int x, int y) {
    int r = x + y;
    // ???????
    boolean overflow = ( (x ^ r) > 0 ) != ( (y ^ r) > 0 );
    if (overflow) {
        throw new ArithmeticException("integer overflow");
    }
    return r;
}

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public static int subtractExact(int x, int y) {
    int r = x - y;
    // ???????
    boolean overflow = ( (x ^ r) > 0 ) != ( (y ^ r) > 0 );
    if (overflow) {
        throw new ArithmeticException("integer overflow");
    }
    return r;
}

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public static int multiplyExact(int x, int y) {
    long r = (long)x * (long)y;
    if ( (int)r != r ) {
        throw new ArithmeticException("integer overflow");
    }
    return (int)r;
}

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public static long multiplyExact(long x, long y) {
    long r = x * y;
    // ???????
    if ( (x == 0 || y == 0) ) {
        return r;
    }
    // ???????
    long ax = Math.abs(x);
    long ay = Math.abs(y);
    if ( (ax > Integer.MAX_VALUE / ay) || (ay > Integer.MAX_VALUE / ax) ) {
        // ????
        long temp = r / y;
        if ( (y != 0) && (temp != x) ) {
            throw new ArithmeticException("long overflow");
        }
        // ??????
        if (x == Long.MIN_VALUE && y == -1) {
            throw new ArithmeticException("long overflow");
        }
    }
    return r;
}