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 1 /**
2      * Returns the value of the {@code long} argument;
3      * throwing an exception if the value overflows an {@code int}.
4      *
5      * @param value the long value
6      * @return the argument as an int
7      * @throws ArithmeticException if the {@code argument} overflows an int
8      * @since 1.8
9      */
10     public static int toIntExact(long value) {
11         if ((int)value != value) {
12             throw new ArithmeticException("integer overflow");
13         }
14         return (int)value;
15     }

long类型的加减乘除运算：

 1   */
2     public static int addExact(int x, int y) {
3         int r = x + y;
4         // HD 2-12 Overflow iff both arguments have the opposite sign of the result
5         if (((x ^ r) & (y ^ r)) < 0) {
6             throw new ArithmeticException("integer overflow");
7         }
8         return r;
9     }
10
11     /**
12      * Returns the sum of its arguments,
13      * throwing an exception if the result overflows a {@code long}.
14      *
15      * @param x the first value
16      * @param y the second value
17      * @return the result
18      * @throws ArithmeticException if the result overflows a long
19      * @since 1.8
20      */
21     public static long addExact(long x, long y) {
22         long r = x + y;
23         // HD 2-12 Overflow iff both arguments have the opposite sign of the result
24         if (((x ^ r) & (y ^ r)) < 0) {
25             throw new ArithmeticException("long overflow");
26         }

 1  public static int subtractExact(int x, int y) {
2         int r = x - y;
3         // HD 2-12 Overflow iff the arguments have different signs and
4         // the sign of the result is different than the sign of x
5         if (((x ^ y) & (x ^ r)) < 0) {
6             throw new ArithmeticException("integer overflow");
7         }
8         return r;
9     }
10
11     /**
12      * Returns the difference of the arguments,
13      * throwing an exception if the result overflows a {@code long}.
14      *
15      * @param x the first value
16      * @param y the second value to subtract from the first
17      * @return the result
18      * @throws ArithmeticException if the result overflows a long
19      * @since 1.8
20      */
21     public static long subtractExact(long x, long y) {
22         long r = x - y;
23         // HD 2-12 Overflow iff the arguments have different signs and
24         // the sign of the result is different than the sign of x
25         if (((x ^ y) & (x ^ r)) < 0) {
26             throw new ArithmeticException("long overflow");
27         }

乘法：

 1 public static int multiplyExact(int x, int y) {
2     long r = (long)x * (long)y;
3     if ((int)r != r) {
4         throw new ArithmeticException("integer overflow");
5     }
6     return (int)r;
7 }
8
9 /**
10  * Returns the product of the arguments,
11  * throwing an exception if the result overflows a {@code long}.
12  *
13  * @param x the first value
14  * @param y the second value
15  * @return the result
16  * @throws ArithmeticException if the result overflows a long
17  * @since 1.8
18  */
19 public static long multiplyExact(long x, long y) {
20     long r = x * y;
21     long ax = Math.abs(x);
22     long ay = Math.abs(y);
23     if (((ax | ay) >>> 31 != 0)) {
24         // Some bits greater than 2^31 that might cause overflow
25         // Check the result using the divide operator
26         // and check for the special case of Long.MIN_VALUE * -1
27        if (((y != 0) && (r / y != x)) ||
28            (x == Long.MIN_VALUE && y == -1)) {
29             throw new ArithmeticException("long overflow");
30         }
31     }
32     return r;
33 }

除法：除法时乡下取整的
 1 public static int floorDiv(int x, int y) {
2         int r = x / y;
3         // if the signs are different and modulo not zero, round down
4         if ((x ^ y) < 0 && (r * y != x)) {
5             r--;
6         }
7         return r;
8     }
9
10 public static long floorDiv(long x, long y) {
11         long r = x / y;
12         // if the signs are different and modulo not zero, round down
13         if ((x ^ y) < 0 && (r * y != x)) {
14             r--;
15         }
16         return r;
17     }

posted on 2020-03-09 19:14  楼子湾  阅读(...)  评论(...编辑  收藏