modulo | 易学教程

Division ( / ) not giving my answer in postgresql

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问题 I have a table software and columns in it as dev_cost , sell_cost . If dev_cost is 16000 and sell_cost is 7500. How do I find the quantity of software to be sold in order to recover the dev_cost ? I have queried as below: select dev_cost / sell_cost from software ; It is returning 2 as the answer. But we need to get 3, right? What would be the query for that? Thanks in advance. 回答1: Your columns have integer types, and integer division truncates the result towards zero. To get an accurate

Is it possible to rewrite modulo (2^n - 1) using bitwise and restricted operators

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For unsigned int x, is it possible to calculate x % 255 (or 2^n - 1 in general) using only the following operators (plus no loop, branch or function call)? ! , ~ , & , ^ , | , + , << , >> . Yes, it's possible. For 255, it can be done as follows: unsigned int x = 4023156861; x = (x & 255) + (x >> 8); x = (x & 255) + (x >> 8); x = (x & 255) + (x >> 8); x = (x & 255) + (x >> 8); // At this point, x will be in the range: 0 <= x < 256. // If the answer 0, x could potentially be 255 which is not fully reduced. // Here's an ugly way of implementing: if (x == 255) x -= 255; // (See comments for a

Fastest modular exponentiation in JavaScript

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问题 My problem is to compute (g^x) mod p quickly in JavaScript, where ^ is exponentiation, mod is the modulo operation. All inputs are nonnegative integers, x has about 256 bits, and p is a prime number of 2048 bits, and g may have up to 2048 bits. Most of the software I've found that can do this in JavaScript seems to use the JavaScript BigInt library (http://www.leemon.com/crypto/BigInt.html). Doing a single exponentiation of such size with this library takes about 9 seconds on my slow browser

Mathematical modulus in c#

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问题 Is there a library function in c# for the mathematical modulus of a number - by this I specifically mean that a negative integer modulo a positive integer should yield a positive result. edited to provide an example: -5 modulo 3 should return 1 回答1: Try (a % b) * Math.Sign(a) Try this; it works correctly. static int MathMod(int a, int b) { return (Math.Abs(a * b) + a) % b; } 回答2: x < 0 ? ((x % m) + m) % m : x % m; 回答3: Well the definition (if I'm not mistaken) is something like this a mod b =

Cube root modulo P — how do I do this?

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问题 I am trying to calculate the cube root of a many-hundred digit number modulo P in Python, and failing miserably. I found code for the Tonelli-Shanks algorithm which supposedly is simple to modify from square roots to cube roots, but this eludes me. I've scoured the web and math libraries and a few books to no avail. Code would be wonderful, so would an algorithm explained in plain English. Here is the Python (2.6?) code for finding square roots: def modular_sqrt(a, p): """ Find a quadratic

Maximum subarray sum modulo M

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问题 Most of us are familiar with the maximum sum subarray problem. I came across a variant of this problem which asks the programmer to output the maximum of all subarray sums modulo some number M. The naive approach to solve this variant would be to find all possible subarray sums (which would be of the order of N^2 where N is the size of the array). Of course, this is not good enough. The question is - how can we do better? Example: Let us consider the following array: 6 6 11 15 12 1 Let M = 13

Ruby: divisible by 4

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This works fine, but I want to make it prettier - and accommodate all values that are divisible by 4: if i==4 || i==8 || i==12 || i==16 || i==20 || i==24 || i==28 || i==32 # ... end Any clever, short method to do this? Sergio Tulentsev Try this: if i % 4 == 0 This is called the " modulo operator ". There's also modulo , which allows you to do 420.modulo(4).zero? There's nothing stopping you doing that with % , but it looks weird: 420.%(4).zero? This is always a good conversation starter: if (i & 3).zero? 来源： https://stackoverflow.com/questions/8817927/ruby-divisible-by-4

How to use mod operator in bash?

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问题 I'm trying a line like this: for i in {1..600}; do wget http://example.com/search/link $i % 5; done; What I'm trying to get as output is: wget http://example.com/search/link0 wget http://example.com/search/link1 wget http://example.com/search/link2 wget http://example.com/search/link3 wget http://example.com/search/link4 wget http://example.com/search/link0 But what I'm actually getting is just: wget http://example.com/search/link 回答1: Try the following: for i in {1..600}; do echo wget http:/

How to Calculate (a/b) %c where a,b and c are 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 5 years ago . I have a function f(x)=(1^1)*(2^2)*(3^3)*.....(x^x) i have to calculate (f(x)/(f(x-r)*f(r)))modulo c i can calculate f(x) and (f(x-r)*f(r)). assume f(x) is a and f(x-r)*f(r) is b. c is some number that is very larger. `` so i how can calculate (a/b)%c 回答1: your f(x) is just ᴨ (PI cumulative multiplication)

mathematics behind modulo behavor

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问题 Preamble This question is not about the behavior of (P)RNG and rand() . It's about using power of two values uniformly distributed against modulo. Introduction I knew that one should not use modulo % to convert a value from a range to another, for example to get a value between 0 and 5 from the rand() function: there will be a bias. It's explained here https://bitbucket.org/haypo/hasard/src/ebf5870a1a54/doc/common_errors.rst?at=default and in this answer Why do people say there is modulo bias