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  • F# - When do you use a type class instead of a record when you do not want to use mutable fields?

    - by fairflow
    I'm imagining a situation where you are creating an F# module in a purely functional style. This means objects do not have mutable fields and are not modified in place. I'm assuming for simplicity that there is no need to use .NET objects or other kinds of objects. There are two possible ways of implementing an object-oriented kind of solution: the first is to use type classes and the second to use records which have fields of functional type, to implement methods. I imagine you'd use classes when you want to use inheritance but that otherwise records would be adequate, if perhaps clumsier to express. Or do you find classes more convenient than records in any case?

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  • Do null SQLite Data fields take up extra memory?

    - by CSharperWithJava
    I'm using the built in sqlite library on the Android platform. I'm considering adding several general purpose fields that users will be able to use for their own custom applications, but these fields will be blank most of the time. My question is, how much overhead will these blank fields add to my database? Do null fields even take up per record memory in sqlite? If so, how much? I don't quite understand the inner workings of a sqlite database.

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  • When to use Shift operators << >> in C# ?

    - by Junior Mayhé
    I was studying shift operators in C#, trying to find out when to use them in my code. I found an answer but for Java, you could: a) Make faster integer multiplication and division operations: *4839534 * 4* can be done like this: 4839534 << 2 or 543894 / 2 can be done like this: 543894 1 Shift operations much more faster than multiplication for most of processors. b) Reassembling byte streams to int values c) For accelerating operations with graphics since Red, Green and Blue colors coded by separate bytes. d) Packing small numbers into one single long... For b, c and d I can't imagine here a real sample. Does anyone know if we can accomplish all these items in C#? Is there more practical use for shift operators in C#?

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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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  • Shift count negative or too big error - correct solution?

    - by PeterK
    I have the following function for reading a big-endian quadword (in a abstract base file I/O class): unsigned long long CGenFile::readBEq(){ unsigned long long qT = 0; qT |= readb() << 56; qT |= readb() << 48; qT |= readb() << 40; qT |= readb() << 32; qT |= readb() << 24; qT |= readb() << 16; qT |= readb() << 8; qT |= readb() << 0; return qT; } The readb() functions reads a BYTE. Here are the typedefs used: typedef unsigned char BYTE; typedef unsigned short WORD; typedef unsigned long DWORD; The thing is that i get 4 compiler warnings on the first four lines with the shift operation: warning C4293: '<<' : shift count negative or too big, undefined behavior I understand why this warning occurs, but i can't seem to figure out how to get rid of it correctly. I could do something like: qT |= (unsigned long long)readb() << 56; This removes the warning, but isn't there any other problem, will the BYTE be correctly extended all the time? Maybe i'm just thinking about it too much and the solution is that simple. Can you guys help me out here? Thanks.

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  • Bitshift in javascript

    - by pingvinus
    I've got a really big number: 5799218898. And want to shift it right to 13 bits. So, windows-calculator or python gives me: 5799218898 13 | 100010100100001110011111100001 13 70791 | 10001010010000111 As expected. But Javascript: 5799218898 13 | 100010100100001110011111100001 13 183624 | 101100110101001000 I think it because of internal integer representation in javascript, but cannot find anything about that.

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  • Interface Builder error: IBXMLDecoder: The value for key is too large to fit into a 32 bit integer

    - by stdout
    I'm working with Robert Payne's fork of PSMTabBarControl that works with IB 3.2 (thanks BTW Robert!): http://codaset.com/robertjpayne/psmtabbarcontrol/. The demo application works fine on 64-bit systems, but when I try to open the XIB file in Interface Builder on a 32-bit system I get: IBXMLDecoder: The value (4654500848) for key (myTrackingRectTag) is too large to fit into a 32 bit integer Building the app as 32 bit works, but then running it gives: PSMTabBarControlDemo[9073:80f] * -[NSKeyedUnarchiver decodeInt32ForKey:]: value (4654500848) for key (myTrackingRectTag) too large to fit in 32-bit integer Not sure if this is a generic IB issue that can occur when moving between 64 and 32 bit systems, or if this is a more specific issue with this code. Has anyone else run into this?

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  • How to return a code value into a variable

    - by Georges Sabbagh
    I have the below case in my report: Receivable: RunningValue(Fields!Receivable.Value,SUM,Nothing) Production: code.SumLookup(LookupSet(Fields!Currency_Type.Value, Fields!Currency_Type1.Value,Fields!Gross_Premium_Amount.Value, "DataSet2")) Rec/Prod: Receivable / Production. Public Function SumLookup(ByVal items As Object()) As Decimal If items Is Nothing Then Return Nothing End If Dim suma As Decimal = New Decimal() Dim ct as Integer = New Integer() suma = 0 ct = 0 For Each item As Object In items suma += Convert.ToDecimal(item) ct += 1 Next If (ct = 0) Then return 0 else return suma End Function The problem is for Rec/Prod, if prod = 0 i receive error. Ive tried to put the below condition: IIF(code.SumLookup(LookupSet(Fields!Currency_Type.Value, Fields!Currency_Type1.Value,Fields!Gross_Premium_Amount.Value, "DataSet2"))=0,0,RunningValue(Fields!Receivable.Value,SUM,Nothing)/(code.SumLookup(LookupSet(Fields!Currency_Type.Value, Fields!Currency_Type1.Value,Fields!Gross_Premium_Amount.Value, "DataSet2")))) but since in the false condition i am recalling code.SumLookup in order to get the value in regetting 0 for production and consiquently i get error for Rec/Prod. how can i call code.sumlookup on time only and save its value into a variable so i dont need to call it everytime i need to check the value. or if there any other solution please advise.

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  • Negative logical shift

    - by user320862
    In Java, why does -32 -1 = 1 ? It's not specific to just -32. It works for all negative numbers as long as they're not too big. I've found that x -1 = 1 x -2 = 3 x -3 = 7 x -4 = 15 given 0 x some large negative number Isn't -1 the same as << 1? But -32 << 1 = -64. I've read up on two's complements, but still don't understand the reasoning.

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  • ARM assembly puzzle

    - by ivant
    First of all, I'm not sure if solution even exists. I spent more than a couple of hours trying to come up with one, so beware. The problem: r1 contains an arbitrary integer, flags are not set according to its value. Set r0 to 1 if r1 is 0x80000000, to 0 otherwise, using only two instructions. It's easy to do that in 3 instructions (there are many ways), however doing it in 2 seems very hard, and may very well be impossible.

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  • Better name for CHAR_BIT?

    - by Potatoswatter
    I was just checking an answer and realized that CHAR_BIT isn't defined by headers as I'd expect, not even by #include <bitset>, on newer GCC. Do I really have to #include <climits> just to get the "functionality" of CHAR_BIT?

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  • How to calculate 2^n-1 efficiently without overflow?

    - by Ludwig Weinzierl
    I want to calculate 2^n-1 for a 64bit integer value. What I currently do is this for(i=0; i<n; i++) r|=1<<i; and I wonder if there is more elegant way to do it. The line is in an inner loop, so I need it to be fast. I thought of r=(1ULL<<n)-1; but it doesn't work for n=64, because << is only defined for values of n up to 63.

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  • ASP.NET MVC2 - specific fields in form pass via a specific object?

    - by ile
    In database I have Contacts table: ContactID (int) FirstName (varchar) LastName (varchar) ... XmlFields (xml) // This field is xml type To create a new contact, I created two classes - one for regular fields and other to display fields from XmlFields field. In Controller, I have following: public ActionResult Create(Contact contact, FormCollection collection) ... Regular field I catch with contact object and those that need to be stored as xml in XmlFields I try to catch with collection object. Problem is that collection object catches all fields, so I wonder if it is possible to isolate xml fields when posting to a specific object so that I can easily manipulate with them. I need this in separated objects because these xml fields are going to be generated dynamically and will be different for every user. Thanks in advance, Ile

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  • Macros to set and clear bits

    - by volting
    Im trying to write a few simple macros to simplify the task of setting and clearing bits which should be a simple task however I cant seem to get them to work correctly. #define SET_BIT(p,n) ((p) |= (1 << (n))) #define CLR_BIT(p,n) ((p) &= (~(1) << (n)))

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  • Setting last N bits in an array

    - by Martin
    I'm sure this is fairly simple, however I have a major mental block on it, so I need a little help here! I have an array of 5 integers, the array is already filled with some data. I want to set the last N bits of the array to be random noise. [int][int][int][int][int] set last 40 bits [unchanged][unchanged][unchanged][24 bits of old data followed 8 bits of randomness][all random] This is largely language agnostic, but I'm working in C# so bonus points for answers in C#

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