Question

我试图写一个＆＃34; BigInteger＆＃34;实现。 BigInteger是一个无符号整数数组。

BigInteger_1 [0] ... BigInteger_1 [15];

我试图添加两个BigInteger。

using System;

namespace BigInt {

    class MainClass {

        static int MAX_SIZE = 16;

        public static void Main () {

            // First BigInteger

            uint[] BigInteger_1 = new uint[MAX_SIZE];

            BigInteger_1 [15] = 0xfffffffe;

            // Second BigInteger

            uint[] BigInteger_2 = new uint[MAX_SIZE];

            BigInteger_2 [15] = 0x00000002;

            // Third BigInteger

            uint[] BigInteger_3 = new uint[MAX_SIZE];

            // Perform an addition

            BigInteger_3 = BigInteger_Add (BigInteger_1, BigInteger_2);

            int i;

            // Print BigInteger_1

            for (i = 1; i < MAX_SIZE; i ++) {

                Console.Write ("{0:x8}", BigInteger_1 [i]);

            }

            Console.WriteLine ();

            // Print BigInteger_2

            for (i = 1; i < MAX_SIZE; i ++) {

                Console.Write ("{0:x8}", BigInteger_2 [i]);

            }

            Console.WriteLine ();

            // Print BigInteger_3

            for (i = 1; i < MAX_SIZE; i ++) {

                Console.Write ("{0:x8}", BigInteger_3 [i]);

            }

            Console.WriteLine ();

        }

        public static uint[] BigInteger_Add (

            uint[] BigInteger_1,

            uint[] BigInteger_2

            ) {

            uint[] BigInteger_3 = new uint[MAX_SIZE];

            uint BigInteger_Carry = 0x00000000;

            uint BigInteger_Limit = 0xffffffff;

            int i;

            // Loop through all integers

            for (i = 1; i < MAX_SIZE; i ++) {

                if (BigInteger_1 [i] + BigInteger_2 [i] >= BigInteger_Limit) {

                    Console.WriteLine ("Check {0} >= {1}", BigInteger_1 [i] + BigInteger_2 [i], BigInteger_Limit);

                    BigInteger_Carry = (BigInteger_1 [i] + BigInteger_2 [i]) - BigInteger_Limit;

                    BigInteger_3 [i] = BigInteger_Limit;

                } else {

                    Console.WriteLine ("Check {0} < {1}", BigInteger_1 [i] + BigInteger_2 [i], BigInteger_Limit);

                    BigInteger_3 [i] = BigInteger_1 [i] + BigInteger_2 [i];

                    BigInteger_Carry = 0x00000000;

                }

            }

            if (BigInteger_Carry != 0x00000000) {

                BigInteger_3 [i] = BigInteger_Carry;

            }

            return BigInteger_3;

        }

    }

}

当我将变量设置为：

// First BigInteger
BigInteger_1 [15] = 0xfffffffe;

// Second BigInteger
BigInteger_2 [15] = 0x00000001;

然后执行后我得到这个输出（向右滚动）：

Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 4294967295 >= 4294967295
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000fffffffe
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000ffffffff

哪个看起来正确。但是当我将变量设置为：

// First BigInteger
BigInteger_1 [15] = 0xfffffffe;

// Second BigInteger
BigInteger_2 [15] = 0x00000002;

我得到了这个（再次滚动）：

Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
Check 0 < 4294967295
0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000fffffffe
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002
000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

因此，如果sum大于最大值，我无法比较两个整数之和和最大值。在这种情况下我能做什么（而且必须做）？

Answer 1

当你添加两个整数时，如果总和大于最大可表示值，则根据定义它无法表示和操作。当你超过最大值时滚动到零是预期的，通常被认为是一个错误条件。

实现您正在尝试的一种低效方法是在BitInteger数组中保留一个额外的整数，您可以在内部维持超过Max_Size的精度。

Answer 2

您正试图检查a + b > uint.MaxValue在a + b溢出时是否有效。{/ p>

解决方案1 ：bool carry = a > uint.MaxValue - b;

解决方案2 ：var result = a + b; bool carry = result < a || result < b;

无符号整数的比较

2 个答案: