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  • Index a mysql table of 3 integer fields

    - by Doori Bar
    I have a mysql table of 3 integer fields. None of the fields have a unique value - but the three of them combined are unique. When I query this table, I only search by the first field. Which approach is recommended for indexing such table? Having a multiple-field primary key on the 3 fields, or setting an index on the first field, which is not unique? Thanks, Doori Bar

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  • Saturated addition of two signed Java 'long' values

    - by finnw
    How can one add two long values (call them x and y) in Java so that if the result overflows then it is clamped to the range Long.MIN_VALUE..Long.MAX_VALUE? For adding ints one can perform the arithmetic in long precision and cast the result back to an int, e.g.: int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; long clampedSum = Math.max((long) Integer.MIN_VALUE, Math.min(sum, (long) Integer.MAX_VALUE)); return (int) clampedSum; } or import com.google.common.primitives.Ints; int saturatedAdd(int x, int y) { long sum = (long) x + (long) y; return Ints.saturatedCast(sum); } but in the case of long there is no larger primitive type that can hold the intermediate (unclamped) sum. Since this is Java, I cannot use inline assembly (in particular SSE's saturated add instructions.) It can be implemented using BigInteger, e.g. static final BigInteger bigMin = BigInteger.valueOf(Long.MIN_VALUE); static final BigInteger bigMax = BigInteger.valueOf(Long.MAX_VALUE); long saturatedAdd(long x, long y) { BigInteger sum = BigInteger.valueOf(x).add(BigInteger.valueOf(y)); return bigMin.max(sum).min(bigMax).longValue(); } however performance is important so this method is not ideal (though useful for testing.) I don't know whether avoiding branching can significantly affect performance in Java. I assume it can, but I would like to benchmark methods both with and without branching. Related: http://stackoverflow.com/questions/121240/saturating-addition-in-c

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  • C/C++: feedback in analyzing a code example

    - by KaiserJohaan
    Hello, I have a piece of code from an assignment I am uncertain about. I feel confident that I know the answer, but I just want to double-check with the community incase there's something I forgot. The title is basically secure coding and the question is just to explain the results. int main() { unsigned int i = 1; unsigned int c = 1; while (i > 0) { i = i*2; c++; } printf("%d\n", c); return 0; } My reasoning is this: At first glance you could imagine the code would run forever, considering it's initialized to a positive value and ever increasing. This of course is wrong because eventually the value will grow so large it will cause an integer overflow. This in turn is not entirely true either, because eventally it will force the variable 'i' to be signed by making the last bit to 1 and therefore regarded as a negative number, therefore terminating the loop. So it is not writing to unallocated memory and therefore cause integer overflow, but rather violating the data type and therefore causing the loop to terminate. I am quite sure this is the reason, but I just want to double check. Any opinions?

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  • Is it guaranteed that new Integer(i) == i in Java?

    - by polygenelubricants
    Consider the following snippet: int i = 99999999; byte b = 99; short s = 9999; Integer ii = Integer.valueOf(9); // should be within cache System.out.println(new Integer(i) == i); // "true" System.out.println(new Integer(b) == b); // "true" System.out.println(new Integer(s) == s); // "true" System.out.println(new Integer(ii) == ii); // "false" It's obvious why the last line will ALWAYS prints "false": we're using == reference identity comparison, and a new object will NEVER be == to an already existing object. The question is about the first 3 lines: are those comparisons guaranteed to be on the primitive int, with the Integer auto-unboxed? Are there cases where the primitive would be auto-boxed instead, and reference identity comparisons are performed? (which would all then be false!)

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  • Finding the Largest and Smallest Integers In A Set- Basic

    - by Ka112324
    I'm kind of on the right track, however my output is not quite right. The program asks for the number of integers you have and then it asks for those numbers. For an example is says please enter the number of integers, you can put 3. And then you enter 3 numbers. I can't use arrays because I am a beginner student and we have not learned those yet. Using count is the only way that allows me to input integers. What do I need to add to my program? Again I am a general computer science student so I can't use anything advanced. I used include iostream, namespace int main and all that you just cant see it int data; int num; int count=0; int max=0; do { cout<<"Enter the number of intergers"<<endl; cin>>num; while (count<num) { cout<<"Please enter a number"<<endl; cin>>data; count++; if (data<min) { min=data; } if (data>max) { max=data; } } cout<<"Smallest integer:"<<min<<endl; cout<<"Largest integer:"<<max<<endl; cout<<"Would you like to continue?"<<endl; cin>>ans; } while ((ans=='y')||(ans=='Y')); return 0; }

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  • SNMP: how to get combined output of memBuffer, memCached and memAvailReal?

    - by user492160
    Below is the output of 'free -m' on my system: total used free shared buffers cached Mem: 2026 1936 90 0 212 649 -/+ buffers/cache: 1074 952 Swap: 3359 0 3359 I'd like to retrieve the value 952 of -/+ buffers/cache using 'snmpwalk'. This is for integrating 'free memory' availability with Cacti-poller. But currently the only values available are: # snmpwalk -v 1 -c public localhost .1.3.6.1.4.1.2021.4 UCD-SNMP-MIB::memIndex.0 = INTEGER: 0 UCD-SNMP-MIB::memErrorName.0 = STRING: swap UCD-SNMP-MIB::memTotalSwap.0 = INTEGER: 3440632 UCD-SNMP-MIB::memAvailSwap.0 = INTEGER: 3440576 UCD-SNMP-MIB::memTotalReal.0 = INTEGER: 2075556 UCD-SNMP-MIB::memAvailReal.0 = INTEGER: 92552 UCD-SNMP-MIB::memTotalFree.0 = INTEGER: 3533128 UCD-SNMP-MIB::memMinimumSwap.0 = INTEGER: 16000 UCD-SNMP-MIB::memShared.0 = INTEGER: 0 UCD-SNMP-MIB::memBuffer.0 = INTEGER: 217388 UCD-SNMP-MIB::memCached.0 = INTEGER: 664904 UCD-SNMP-MIB::memSwapError.0 = INTEGER: 0 UCD-SNMP-MIB::memSwapErrorMsg.0 = STRING: Is it possible to retrieve the combined value of memBuffer+memCached+memAvailReal using snmpwalk for graphing with Cacti and RRDTool? If not what options do I possibly have? I'm using net-snmp 5.3.2 on my agent host. Thanks in advance.

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  • Passing integer lists in a sql query, best practices

    - by Artiom Chilaru
    I'm currently looking at ways to pass lists of integers in a SQL query, and try to decide which of them is best in which situation, what are the benefots of each, and what are the pitfalls, what should be avoided :) Right now I know of 3 ways that we currently use in our application. 1) Table valued parameter: Create a new Table Valued Parameter in sql server: CREATE TYPE [dbo].[TVP_INT] AS TABLE( [ID] [int] NOT NULL ) Then run the query against it: using (var conn = new SqlConnection(DataContext.GetDefaultConnectionString)) { var comm = conn.CreateCommand(); comm.CommandType = CommandType.Text; comm.CommandText = @" UPDATE DA SET [tsLastImportAttempt] = CURRENT_TIMESTAMP FROM [Account] DA JOIN @values IDs ON DA.ID = IDs.ID"; comm.Parameters.Add(new SqlParameter("values", downloadResults.Select(d => d.ID).ToDataTable()) { TypeName = "TVP_INT" }); conn.Open(); comm.ExecuteScalar(); } The major disadvantages of this method is the fact that Linq doesn't support table valued params (if you create an SP with a TVP param, linq won't be able to run it) :( 2) Convert the list to Binary and use it in Linq! This is a bit better.. Create an SP, and you can run it within linq :) To do this, the SP will have an IMAGE parameter, and we'll be using a user defined function (udf) to convert this to a table.. We currently have implementations of this function written in C++ and in assembly, both have pretty much the same performance :) Basically, each integer is represented by 4 bytes, and passed to the SP. In .NET we have an extension method that convers an IEnumerable to a byte array The extension method: public static Byte[] ToBinary(this IEnumerable intList) { return ToBinaryEnum(intList).ToArray(); } private static IEnumerable<Byte> ToBinaryEnum(IEnumerable<Int32> intList) { IEnumerator<Int32> marker = intList.GetEnumerator(); while (marker.MoveNext()) { Byte[] result = BitConverter.GetBytes(marker.Current); Array.Reverse(result); foreach (byte b in result) yield return b; } } The SP: CREATE PROCEDURE [Accounts-UpdateImportAttempts] @values IMAGE AS BEGIN UPDATE DA SET [tsLastImportAttempt] = CURRENT_TIMESTAMP FROM [Account] DA JOIN dbo.udfIntegerArray(@values, 4) IDs ON DA.ID = IDs.Value4 END And we can use it by running the SP directly, or in any linq query we need using (var db = new DataContext()) { db.Accounts_UpdateImportAttempts(downloadResults.Select(d => d.ID).ToBinary()); // or var accounts = db.Accounts .Where(a => db.udfIntegerArray(downloadResults.Select(d => d.ID).ToBinary(), 4) .Select(i => i.Value4) .Contains(a.ID)); } This method has the benefit of using compiled queries in linq (which will have the same sql definition, and query plan, so will also be cached), and can be used in SPs as well. Both these methods are theoretically unlimited, so you can pass millions of ints at a time :) 3) The simple linq .Contains() It's a more simple approach, and is perfect in simple scenarios. But is of course limited by this. using (var db = new DataContext()) { var accounts = db.Accounts .Where(a => downloadResults.Select(d => d.ID).Contains(a.ID)); } The biggest drawback of this method is that each integer in the downloadResults variable will be passed as a separate int.. In this case, the query is limited by sql (max allowed parameters in a sql query, which is a couple of thousand, if I remember right). So I'd like to ask.. What do you think is the best of these, and what other methods and approaches have I missed?

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  • Looking for more details about "Group varint encoding/decoding" presented in Jeff's slides

    - by Mickey Shine
    I noticed that in Jeff's slides "Challenges in Building Large-Scale Information Retrieval Systems", which can also be downloaded here: http://research.google.com/people/jeff/WSDM09-keynote.pdf, a method of integers compression called "group varint encoding" was mentioned. It was said much faster than 7 bits per byte integer encoding (2X more). I am very interested in this and looking for an implementation of this, or any more details that could help me implement this by myself. I am not a pro and new to this, and any help is welcome!

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  • Add and Subtract 128 Bit Integers in C(++)

    - by Billy ONeal
    Hello :) I'm writing a compressor for a long stream of 128 bit numbers. I would like to store the numbers as differences -- storing only the difference between the numbers rather than the numbers themselves because I can pack the differences in fewer bytes because they are smaller. However, for compression then I need to subtract these 128 bit values, and for decompression I need to add these values. Maximum integer size for my compiler is 64 bits wide. Anyone have any ideas for doing this efficiently? Billy3

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  • Java Interger: what is faster comparison or subtraction?

    - by Vladimir
    I've found that java.lang.Ingteger implementation of compareTo method looks as follows: public int compareTo(Integer anotherInteger) { int thisVal = this.value; int anotherVal = anotherInteger.value; return (thisVal<anotherVal ? -1 : (thisVal==anotherVal ? 0 : 1)); } The question is why use comparison instead of subtraction: return thisVal - anotherVal;

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  • Converting String to int in Java and getting a NumberFormatException, can't figure out why

    - by user1687682
    ipString is a String representation of an IP address with spaces instead of dots. String[] ipArray = ipString.split(" "); String ip = ""; for (String part : ipArray){ if (part != null){ ip += part } } ip = ip.trim(); int ipInt = Integer.parseInt(ip); // Exception is thrown here. Exception in thread "main" java.lang.NumberFormatException: For input string: "6622015176". Could someone explain why this exception is being thrown?

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  • Problem getting size of Website Xcode

    - by Michael Amici
    When i try and compile I come up with a warning that reads initialization makes pointer from integer without a cast. No clue why. I am just trying to get the size of a website. #import "Lockerz_RedemptionViewController.h" @implementation Lockerz_RedemptionViewController -(IBAction)startLoop:(id) sender { NSData *dataNew = [NSData dataWithData:[NSData dataWithContentsOfURL:[NSURL URLWithString:@"http://www.google.com/"]]]; NSUInteger *len = [dataNew length]; //error is here NSLog(@"%@", len); }

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  • Is there a view for inputing integers in Android?

    - by J. Pablo Fernández
    I'm looking for something like the individual parts of the date picker dialog. A view that allows you to input integers (and only integers) that you can limit (between 1 and 10 for example), where you can use the keyboard or the arrows in the view itself. Does it exists? It is for a dialog. A ready-made dialog to request an integer would also help.

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  • Integer ID obfuscation techniques

    - by Chris
    Hi there, I'm looking for an easy and reversible method of obfuscating integer IDs. Ideally, I'd want the resulting obfuscation to be at most eight characters in length and non-sequential, meaning that the obfuscation of "1" should look nothing like the obfuscation for "2" and so on. This isn't meant to be secure by any means, so this isn't a huge concern. Additionally, the integers I'll be obfuscating aren't large - between one and 10,000 - but I don't want any collisions, either. Does anybody have any ideas for something that would fit this criteria? Thanks! Chris

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  • C Programming - Convert an integer to binary

    - by leo
    Hi guys - i was hopefully after some tips opposed to solutions as this is homework and i want to solve it myself I am firstly very new to C. In fact i have never done any before, though i have previous java experience from modules at university. I am trying to write a programme that converts a single integer in to binary. I am only allowed to use bitwise operations and no library functions Can anyone possibly suggest some ideas about how i would go about doing this. Obviously i dont want code or anything, just some ideas as to what avenues to explore as currenty i am a little confused and have no plan of attack. Well, make that a lot confused :D thanks very much

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  • JAVA: Sort ArrayList<ArrayList<Integer>> on multiple columns

    - by Bob
    First, I did do my homework searching before posting here. My requirement seems to be slightly different compared to questions posted out there. I have a matrix like ArrayList<ArrayList<Integer>> in the following form | id1 | id2 | score | |-----|-----|-------| | 1 | 3 | 95% | | 1 | 2 | 100% | | 1 | 4 | 85% | | 1 | 5 | 95% | | 2 | 10 | 80% | | 2 | 15 | 99% | I want to sort the matrix column-wise (first using score, then the id1). I already have the id1 in a sorted manner. That means I also need to sort all records with the same id1 first by using score, second by the id2. The reason for doing this is to create a ranking of the id2 in each id1. The result for the above example would be: | q_id | d_id | rank | score | |------|------|------|-------| | 1 | 2 | 1 | 100% | | 1 | 3 | 2 | 95% | | 1 | 5 | 3 | 95% | | 1 | 4 | 4 | 85% | | 2 | 15 | 1 | 99% | | 2 | 10 | 2 | 80% | How can I achieve this in Java using some built-in methods of collections?

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  • Batch File input validation - Make sure user entered an integer

    - by B2Ben
    I'm experimenting with a DOS batch file to perform a simple operation which requires the user to enter a non-negative integer. I'm using simple batch-file techniques to get user input: @ECHO OFF SET /P UserInput=Please Enter a Number: The user can enter any text they want here, so I would like to add some routine to make sure what the user entered was a valid number. That is... they entered at least one character, and every character is a number from 0 to 9. I'd like something I can feed the UserInput into. At the end of the routine would be like an if/then that would run different statements based on whether or not it was actually a valid number. I've experimented with loops and substrings and such, but my knowledge and understanding is still slim... so any help would be appreciated. I could build an executable, and I know there are nicer ways to do things than batch files, but at least for this task I'm trying to keep it simple by using a batch file.

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  • Packing a long binary integer in Ruby

    - by user1056142
    I'm trying to send a very long binary integer over UDP (on the order of 200 bits). When I try to use Array's pack method, it complains the string I'm trying to convert is too large. Am I going about this the wrong way? ruby-1.8.7-p352 :003 > [0b1101001010101101111010100101010011010101010110010101010101010010010101001010101010101011101010101010101111010101010101010101].pack('i') RangeError: bignum too big to convert into `unsigned long' from (irb):3:in `pack' from (irb):3 This number is supposed to represent a DNS query packet (this is for a homework assignment; we're not allowed to use any DNS libraries).

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  • text indexes vs integer indexes in mysql

    - by imanc
    Hey, I have always tried to have an integer primary key on a table no matter what. But now I am questioning if this is always necessary. Let's say I have a product table and each product has a globally unique SKU number - that would be a string of say 8-16 characters. Why not make this the PK? Typically I would make this field a unique index but then have an auto incrementing int field as the PK, as I assumed it would be faster, easier to maintain, and would allow me to do things like get the last 5 records added with ease. But in terms of optimisation, assuming I'd only ever be matching the full text field and next doing text matching queries (e.g. like %%) can you guys think of any reasons not to use a text based primary key, most likely of type varchar()? Cheers, imanc

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  • Fluent NHibernate - Unable to parse integer as enum.

    - by Aaron Smith
    I have a column mapped to an enum with a convention set up to map this as an integer to the database. When I run the code to pull the data from the database I get the error "Can't Parse 4 as Status" public class Provider:Entity<Provider> { public virtual Enums.ProviderStatus Status { get; set; } } public class ProviderMap:ClassMap<Provider> { public ProviderMap() { Map(x => x.Status); } } class EnumConvention:IUserTypeConvention { public void Accept(IAcceptanceCriteria<IPropertyInspector> criteria) { criteria.Expect(x => x.Property.PropertyType.IsEnum); } public void Apply(IPropertyInstance instance) { instance.CustomType(instance.Property.PropertyType); } } Any idea what I'm doing wrong?

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