integer-overflow | 易学教程

Why may an overflow occur in the following program?

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问题 void main () { int i; if (i < 0) { i = -i; }; } Can anyone help me to understand why an overflow may occur in the above program? 回答1: An overflow may occur because the range of integer representation in two's complement is not symmetric: the magnitude of the smallest negative number that can be represented is the magnitude of the highest positive number that can be represented, plus one. For example, on a 32-bit system the values are -2,147,483,648 and 2,147,483,647 . That's why negating -2

Panicked at 'attempt to subtract with overflow' when cycling backwards though a list

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问题 I am writing a cycle method for a list that moves an index either forwards or backwards. The following code is used to cycle backwards: (i-1)%list_length In this case, i is of the type usize , meaning it is unsigned. If i is equal to 0, this leads to an 'attempt to subtract with overflow' error. I tried to use the correct casting methods to work around this problem: ((i as isize)-1)%(list_length as isize)) as usize This results in an integer overflow. I understand why the errors happen, and

First digit of the product of two very large numbers [closed]

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问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 3 years ago . There are 2 large integers, x and y such that z=x*y overflows. I would like to compute the first digit of x. Directly doing so isn't possible as the result overflows. I was wondering if there was a certain technique for this. Example: 10000000000000000000000000000000000 * 20579725928294522859735727575, here the

How can i define a List of checked integers

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问题 I have a List of Integers defined as List<int> myIntList = new List<int>(); As usual I will add value to the list using myIntList.Add() method. The problem I am facing is that the values in the list are dynamic(result of some calculation) that may exceed the maximum value that an integer can hold. Consider the following scenario: int x = int.MaxValue; myIntList.Add(x + 1); This will add -2147483648 to the list instead of throwing an exception. I need to throw an exception here. I know

How to suppress overflow-checking in PowerShell?

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问题 PowerShell seems to perform bounds-checking after arithmetic operations and conversions. For instance, the following operations fail: [byte]$a = 255 $a++ $a = [byte]256 Is there any way to enforce overflows or the typecast without resorting to a manual calculation via modulo or C# and Add-Type? 回答1: The behavior you want in PowerShell is achievable, though, it's a bit of a hack; and maybe there's a better way. If you just want cryptographic functionality though, it's worth calling out, that

why left+(right-left)/2 will not overflow?

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问题 In this article: http://googleresearch.blogspot.sg/2006/06/extra-extra-read-all-about-it-nearly.html, it mentioned most quick sort algorithm had a bug (left+right)/2, and it pointed out that the solution was using left+(right-left)/2 instead of (left+right)/2 . The solution was also given in question Bug in quicksort example (K&R C book)? My question is why left+(right-left)/2 can avoid overflow? How to prove it? Thanks in advance. 回答1: You have left < right by definition. As a consequence,

What would happen if I were to make more references to Objects than 32 bits can account for?

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问题 So I just learned when you declare a variable of type Object ( i.e. Object a; ), a 32-bit space is allocated for that variable. Inside this variable/reference, there is a memory address to an actual Object. Now let's pretend I have a large enough amount of memory to do this. What would happen if I created more than 4,294,967,296 (2 32 ) variables of type Object and tried assigning them to a distinct Object? Would some variables/references get the same memory addresses due to integer overflow?

How to simulate 32-bit signed integer overflow in PL/SQL?

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问题 Do you know how to simulate a 32-bit integer overflow in Oracle PL/SQL. For instance, 2147483647 + 1 = -2147483648 or -2147483648 - 1 = 212147483647 I tried PLS_INTEGER, but it throws an overflow exception. 回答1: Perhaps you could trap the overflow exception, as in the following: DECLARE n PLS_INTEGER; addend PLS_INTEGER; NUMERIC_OVERFLOW EXCEPTION; PRAGMA EXCEPTION_INIT(NUMERIC_OVERFLOW, -1426); BEGIN n := 2147483642; addend := 6; BEGIN n := n + addend; EXCEPTION WHEN NUMERIC_OVERFLOW THEN

double precision integer subtraction with 32-bit registers(MIPS)

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问题 I am learning computer arithmetic. The book I use(Patterson and Hennessey) lists the below question. Write mips code to conduct double precision integer subtraction for 64-bit data. Assume the first operand to be in registers $t4(hi) and $t5(lo), second in $t6(hi) and $t7(lo). My solution to the answer is sub $t3, $t5, $t7 # Subtract lo parts of operands. t3 = t5 - t7 sltu $t2, $t5, $t7 # If the lo part of the 1st operand is less than the 2nd, # it means a borrow must be made from the hi part

C++ literal integer type

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Do literal expressions have types too ? long long int a = 2147483647+1 ; long long int b = 2147483648+1 ; std::cout << a << ',' << b ; // -2147483648,2147483649 Yes, literal numbers have types. The type of an unsuffixed decimal integer literal is the first of int , long , long long in which the integer can be represented. The type of binary, hex and octal literals is selected similarly but with unsigned types in the list as well. You can force the use of unsigned types by using a U suffix. If you use a single L in the suffix then the type will be at least long but it might be long long if it