math

问题 I already have a 64 bit hash function in a library (C coding), but I only need 48 bits. I need to trim down the 64 bit hash value to a 48 bit value, yet it has to be in a safe manner in order to minimize collision. The hash function is a very good 64 bit hash function. It has been tested with SMHasher (the "DieHarder" hash testing) and proved better than Murmur2. According to my colleagues, the algorithm implemented in the lib for 64-bit hashing is xxHash, tested with SMHasher and got a Q

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 6 years ago . I am extreamly interested in math and programming and planning to start symbolic math project from scratch . Is this good project idea? Where to start? How should one approach this project? Any good resources? Thanks in advance. 回答1: It's a good project to practice

问题 Closed . This question is opinion-based. It is not currently accepting answers. Want to improve this question? Update the question so it can be answered with facts and citations by editing this post. Closed 6 years ago . I am extreamly interested in math and programming and planning to start symbolic math project from scratch . Is this good project idea? Where to start? How should one approach this project? Any good resources? Thanks in advance. 回答1: It's a good project to practice

问题 After I have seen a lot of questions here using the DATE_SUB() or DATE_ADD() functions instead of the arithmetic operators + or - , I was wondering if there was any difference: Quote from the MySQL-manual: Date arithmetic also can be performed using INTERVAL together with the + or - operator: date + INTERVAL expr unit date - INTERVAL expr unit So basically, these two statements return the same result: SELECT DATE_ADD(NOW(), INTERVAL 7 DAY); and SELECT NOW() + INTERVAL 7 DAY; Now my question:

问题 I want to generate a list of all possible combinations of a list of strings (it's actually a list of objects, but for simplicity we'll use strings). I need this list so that I can test every possible combination in a unit test. So for example if I have a list of: var allValues = new List<string>() { "A1", "A2", "A3", "B1", "B2", "C1" } I need a List<List<string>> with all combinations like: A1 A2 A3 B1 B2 C1 A1 A2 A1 A2 A3 A1 A2 A3 B1 A1 A2 A3 B1 B2 A1 A2 A3 B1 B2 C1 A1 A3 A1 A3 B1 etc... A

问题 I want to generate a list of all possible combinations of a list of strings (it's actually a list of objects, but for simplicity we'll use strings). I need this list so that I can test every possible combination in a unit test. So for example if I have a list of: var allValues = new List<string>() { "A1", "A2", "A3", "B1", "B2", "C1" } I need a List<List<string>> with all combinations like: A1 A2 A3 B1 B2 C1 A1 A2 A1 A2 A3 A1 A2 A3 B1 A1 A2 A3 B1 B2 A1 A2 A3 B1 B2 C1 A1 A3 A1 A3 B1 etc... A

问题 I want to generate a list of all possible combinations of a list of strings (it's actually a list of objects, but for simplicity we'll use strings). I need this list so that I can test every possible combination in a unit test. So for example if I have a list of: var allValues = new List<string>() { "A1", "A2", "A3", "B1", "B2", "C1" } I need a List<List<string>> with all combinations like: A1 A2 A3 B1 B2 C1 A1 A2 A1 A2 A3 A1 A2 A3 B1 A1 A2 A3 B1 B2 A1 A2 A3 B1 B2 C1 A1 A3 A1 A3 B1 etc... A

问题 I want to generate a list of all possible combinations of a list of strings (it's actually a list of objects, but for simplicity we'll use strings). I need this list so that I can test every possible combination in a unit test. So for example if I have a list of: var allValues = new List<string>() { "A1", "A2", "A3", "B1", "B2", "C1" } I need a List<List<string>> with all combinations like: A1 A2 A3 B1 B2 C1 A1 A2 A1 A2 A3 A1 A2 A3 B1 A1 A2 A3 B1 B2 A1 A2 A3 B1 B2 C1 A1 A3 A1 A3 B1 etc... A

问题 How can I resize and reposition the image inside a box, in such way that it covers the entire box, similar to how background-size: cover works. <div class="box" style="width: 100px; height: 100px;"> <img src="pic.jpg" width="413" height="325"> </div> I know I have to add overflow:hidden to the box and the image needs position: absolute . But what's the formula that gets me the right new size for the image, and left + top positions? 回答1: this may be easier jQuery $('.box').each(function() { /

问题 How can I resize and reposition the image inside a box, in such way that it covers the entire box, similar to how background-size: cover works. <div class="box" style="width: 100px; height: 100px;"> <img src="pic.jpg" width="413" height="325"> </div> I know I have to add overflow:hidden to the box and the image needs position: absolute . But what's the formula that gets me the right new size for the image, and left + top positions? 回答1: this may be easier jQuery $('.box').each(function() { /