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  • Is It Worth Using Bitwise Operators In Methods?

    - by user1626141
    I am very new to Java (and programming in general, my previous experience is with ActionScript 2.0 and some simple JavaScript), and I am working my way slowly and methodically through Java: A Beginner's Guide by Herbert Schildt. It is an incredible book. For one thing, I finally understand more-or-less what bitwise operators (which I first encountered in ActionScript 2.0) do, and that they are more efficient than other methods for certain sums. My question is, is it more efficient to use a method that uses, say, a shift right, to perform all your divisions/2 (or divisions/even) for you in a large program with many calculations (in this case, a sprawling RPG), or is it more efficient to simply use standard mathematical operations because the compiler will optimise it all for you? Or, am I asking the wrong question entirely?

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  • bitwise XOR a string in Bash

    - by ricky2002
    Hi. I am trying to accomplish a work in Bash scripting. I have a string which i want to XOR with my key. #!/bin/sh PATH=/bin:/usr/bin:/sbin:/usr/sbin export PATH teststring="abcdefghijklmnopqr" Now how do i XOR the value of teststring and store it in a variable using bash? Any help will be appreciated.

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  • Rerversing AND Bitwise.

    - by Benjamin
    Hey all, Here's the following algorithm: int encryption(int a, int b) { short int c, c2; uint8_t d; c = a ^ b; c2 = c; d = 0; while(c) { c &= c - 1; d++; } return d; } How can I find which variable a and b I should send in that function to decide of the output value of d? In other words, how can I reverse the algoritm to let's say if I want d=11?

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  • Finding shared list IDs in a MySQL table using bitwise operands

    - by landons
    I want to find items in common from the "following_list" column in a table of users: +----+--------------------+-------------------------------------+ | id | name | following_list | +----+--------------------+-------------------------------------+ | 9 | User 1 | 26,6,12,10,21,24,19,16 | | 10 | User 2 | 21,24 | | 12 | User 3 | 9,20,21,26,30 | | 16 | User 4 | 6,52,9,10 | | 19 | User 5 | 9,10,6,24 | | 21 | User 6 | 9,10,6,12 | | 24 | User 7 | 9,10,6 | | 46 | User 8 | 45 | | 52 | User 9 | 10,12,16,21,19,20,18,17,23,25,24,22 | +----+--------------------+-------------------------------------+ I was hoping to be able to sort by the number of matches for a given user id. For example, I want to match all users except #9 against #9 to see which of the IDs in the "following_list" column they have in common. I found a way of doing this through the "SET" datatype and some bit trickery: http://dev.mysql.com/tech-resources/articles/mysql-set-datatype.html#bits However, I need to do this on an arbitrary list of IDs. I was hoping this could be done entirely through the database, but this is a little out of my league. Any bit gurus out there? Thanks, Landon

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  • How to manually (bitwise) perform (float)x? (homework)

    - by Silver
    Now, here is the function header of the function I'm supposed to implement: /* * float_from_int - Return bit-level equivalent of expression (float) x * Result is returned as unsigned int, but * it is to be interpreted as the bit-level representation of a * single-precision floating point values. * Legal ops: Any integer/unsigned operations incl. ||, &&. also if, while * Max ops: 30 * Rating: 4 */ unsigned float_from_int(int x) { ... } We aren't allowed to do float operations, or any kind of casting. Now I tried to implement the first algorithm given at this site: http://locklessinc.com/articles/i2f/ Here's my code: unsigned float_from_int(int x) { // grab sign bit int xIsNegative = 0; int absValOfX = x; if(x < 0){ xIsNegative = 1; absValOfX = -x; } // zero case if(x == 0){ return 0; } //int shiftsNeeded = 0; /*while(){ shiftsNeeded++; }*/ unsigned I2F_MAX_BITS = 15; unsigned I2F_MAX_INPUT = ((1 << I2F_MAX_BITS) - 1); unsigned I2F_SHIFT = (24 - I2F_MAX_BITS); unsigned result, i, exponent, fraction; if ((absValOfX & I2F_MAX_INPUT) == 0) result = 0; else { exponent = 126 + I2F_MAX_BITS; fraction = (absValOfX & I2F_MAX_INPUT) << I2F_SHIFT; i = 0; while(i < I2F_MAX_BITS) { if (fraction & 0x800000) break; else { fraction = fraction << 1; exponent = exponent - 1; } i++; } result = (xIsNegative << 31) | exponent << 23 | (fraction & 0x7fffff); } return result; } But it didn't work (see test error below): Test float_from_int(-2147483648[0x80000000]) failed... ...Gives 0[0x0]. Should be -822083584[0xcf000000] 4 4 0 float_times_four I don't know where to go from here. How should I go about parsing the float from this int?

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  • DWORD to bytes using bitwise shift operators

    - by Dave18
    I can't get it to work correctly. #include <windows.h> int main() { DWORD i = 6521; BYTE first = i >> 32; BYTE second = i >> 24; BYTE third = i >> 16; BYTE fourth = i >> 8; i = (((DWORD)fourth) << 24) | (((DWORD)third) << 16) | (((DWORD)second) << 8) | first; }

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  • Bitwise setting in C++

    - by Sunil
    enum AccessSource { AccessSourceNull = 0x00000001, AccessSourceSec = 0x00000002, AccessSourceIpo = 0x00000004, AccessSourceSSA = 0x00000008, AccessSourceUpgrade = 0x00000010, AccessSourceDelta = 0x00000020, AccessSourcePhoneM = 0x00000040, AccessSourceSoft = 0x00000080, AccessSourceCR = 0x00000100, AccessSourceA = 0x00000200, AccessSourceE = 0x00000400, AccessSourceAll = 0xFFFFFFFF }; What is the value of AccessSourceAll ?? is it -1? or is it maximum value? I have a parameter ULONG x , whose default value is AccessSourceAll(that means access to all). How do i remove the access right of AccessSourceE only? How to add the access right of AccessSourceE again? If i have a particular value in x, then how do i know whether AccessSourceE is set or not?

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  • implementing cryptographic algorithms, specifically the key expansion part

    - by masseyc
    Hey, recently I picked up a copy of Applied Cryptography by Bruce Schneier and it's been a good read. I now understand how several algorithms outlined in the book work, and I'd like to start implementing a few of them in C. One thing that many of the algorithms have in common is dividing an x-bit key, into several smaller y-bit keys. For example, blowfish's key, X, is 64-bits, but you are required to break it up into two 32-bit halves; Xl and Xr. This is where I'm getting stuck. I'm fairly decent with C, but I'm not the strongest when it comes to bitwise operators and the like. After some help on IRC, I managed to come up with these two macros: #define splitup(a, b, c) {b = a >> 32; c = a & 0xffffffff; } #define combine(a, b, c) {a = (c << 32) | a;} Where a is 64 bits and b and c are 32 bits. However, the compiler warns me about the fact that I'm shifting a 32 bit variable by 32 bits. My questions are these: what's bad about shifting a 32-bit variable 32 bits? I'm guessing it's undefined, but these macros do seem to be working. Also, would you suggest I go about this another way? As I said, I'm fairly familiar with C, but bitwise operators and the like still give me a headache.

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  • Unary NOT/Integersize of the architecture

    - by sid_com
    From "Mastering Perl/Chapter 16/Bit Operators/Unary NOT,~": The unary NOT operator (sometimes called the complement operator), ~, returns the bitwise negation, or 1's complement, of the value, based on integer size of the architecture Why does the following script output two different values? #!/usr/local/bin/perl use warnings; use 5.012; use Config; my $int_size = $Config{intsize} * 8; my $value = 0b1111_1111; my $complement = ~ $value; say length sprintf "%${int_size}b", $value; say length sprintf "%${int_size}b", $complement; Output: 32 64

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  • Boolean Not operator in VBScript

    - by Lumi
    Consider the following two conditionals (involving bitwise comparisons) in VBScript: If 1 And 3 Then WScript.Echo "yes" Else WScript.Echo "no" If Not(1 And 3) Then WScript.Echo "yes" Else WScript.Echo "no" Prints first yes, then no, right? cscript not.vbs Wrong! It prints yes twice! Wait a second, the Not operator is supposed to perform logical negation on an expression. The logical negation of true is false, as far as I know. Must I conclude that it doesn't live up to that promise? How and why and what is going on here? What is the rationale, if any?

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  • Help translating Reflector deconstruction into compilable code

    - by code poet
    So I am Reflector-ing some framework 2.0 code and end up with the following deconstruction fixed (void* voidRef3 = ((void*) &_someMember)) { ... } This won't compile due to 'The right hand side of a fixed statement assignment may not be a cast expression' I understand that Reflector can only approximate and generally I can see a clear path but this is a bit outside my experience. Question: what is Reflector trying to describe to me? Update: Am also seeing the following fixed (IntPtr* ptrRef3 = ((IntPtr*) &this._someMember)) Update: So, as Mitch says, it is not a bitwise operator, but an addressOf operator. Question is now: fixed (IntPtr* ptrRef3 = &_someMember) fails with an 'Cannot implicitly convert type 'xxx*' to 'System.IntPtr*'. An explicit conversion exists (are you missing a cast?)' compilation error. So I seemed to be damned if I do and damned if I dont. Any ideas?

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  • Trying to figure out how to check a checksum

    - by rross
    I'm trying to figure out how to check a checksum. My message looks like this: 38 0A 01 12 78 96 FE 00 F0 FB D0 FE F6 F6 being the checksum. I convert the preceding 12 sets in to binary and then add them together. Then attempt a bitwise operation to apply the 2s complement. I get a value of -1562, but I can't convert it back to hex to check if the value is correct. Can someone point me in the right direction? my code: string[] hexValue = {"38", "0A", "01", "12", "78", "96", "FE", "00", "F0", "FB", "D0", "FE"}; int totalValue = 0; foreach(string item in hexValue) { totalValue += Int32.Parse(item, NumberStyles.HexNumber); } int bAfter2sC = ~totalValue + 1; Console.Write("answer :" + bAfter2sC + "\n");

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  • C++ 64bit issue

    - by Bobby
    I have the following code: tmp_data = simulated_data[index_data]; unsigned char *dem_content_buff; dem_content_buff = new unsigned char [dem_content_buff_size]; int tmp_data; unsigned long long tmp_64_data; if (!(strcmp(dems[i].GetValType(), "s32"))) { dem_content_buff[BytFldPos] = tmp_data; dem_content_buff[BytFldPos + 1] = tmp_data >> 8; dem_content_buff[BytFldPos + 2] = tmp_data >> 16; dem_content_buff[BytFldPos + 3] = tmp_data >> 24; } if (!(strcmp(dems[i].GetValType(), "f64"))) { dem_content_buff[BytFldPos] = tmp_data; dem_content_buff[BytFldPos + 1] = tmp_data >> 8; dem_content_buff[BytFldPos + 2] = tmp_data >> 16; dem_content_buff[BytFldPos + 3] = tmp_data >> 24; dem_content_buff[BytFldPos + 4] = tmp_data >> 32; dem_content_buff[BytFldPos + 5] = tmp_data >> 40; dem_content_buff[BytFldPos + 6] = tmp_data >> 48; dem_content_buff[BytFldPos + 7] = tmp_data >> 56; } I am getting some weird memory errors in other places of the application when the second if statement is true and executed. When I comment out the 2nd if statement, the problem works fine. So I suspect the way I am performing bitwise operations for 64bit data is incorrect. Can anyone see anything in this code that needs to be corrected?

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  • Where would I use a bitwise operator in JavaScript?

    - by J-P
    I've read this (http://stackoverflow.com/quest...), so I know what bitwise operators are but I'm still not clear on how one might use them... Can anyone offer any real-world examples of where a bitwise operator would be useful in JavaScript? Thanks. Edit: Just digging into the jQuery source I've found a couple of places where bitwise operators are used, for example: (only the & operator) // Line 2756: event.which = (event.button & 1 ? 1 : ( event.button & 2 ? 3 : ( event.button & 4 ? 2 : 0 ) )); // Line 2101 var ret = a.compareDocumentPosition(b) & 4 ? -1 : a === b ? 0 : 1;

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  • bit manipulation in java

    - by sarav
    I have a fragment of bytes in a byte[]. The total size of the array is 4 and I want to convert this into a positive long number. For example if the byte array is having four bytes 101, 110, 10, 1 then i want to get the long number represented by binary sequence 00000000 00000000 00000000 00000000 00000101 00000110 00000010 00000001 which equals 84279809 What is the efficient way to do that in Java?

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  • Workaround for basic syntax not being parsed.

    - by Mark Tomlin
    I want to have a class property that allow for an expression to take place on the right side of the equals sign. All versions of PHP choke on the following code, but it is written in this way to allow for easier extendibility in the future. /* Example SDK Class */ class SDK { /* Runtime Option Flags */ // Strings # 0: Makes no change to the strings. var $STRING_NONE = (1 << 0); # 1: Removes color codes from the string. var $STRING_STRIP_COLOR = (1 << 1); # 2: Removes language codes from the string. var $STRING_STRIP_LANG = (1 << 2); # 3: Removes all formatting from the string. var $STRING_STRIP = SELF::STRING_STRIP_COLOR & SELF::STRING_STRIP_LANG; # 4: Converts color codes to HTML & UTF-8. var $STRING_HTML = (1 << 3); # 8: Converts color codes to ECMA-48 escape color codes & UTF-8. var $STRING_CONSOLE = (1 << 4); # 16: Changes player names only. var $STRING_NAMES = (1 << 5); # 32: Changes host names only. var $STRING_HOSTS = (1 << 6); function SDK($fString = SELF::STRING_HTML & SELF::STRING_NAMES & SELF_HOST) { // constructor code. } } $SDK &= new SDK(SDK::STRING_NONE); (1 << 0) seems like very basic syntax to me, and is not fathomable why PHP would not allow for such a thing. Can anyone think of a work around that would maintain readability and future expandability of the following code?

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  • A question in java.lang.Integer internal code

    - by Daziplqa
    Hi folks, While looking in the code of the method: Integer.toHexString I found the following code : public static String toHexString(int i) { return toUnsignedString(i, 4); } private static String toUnsignedString(int i, int shift) { char[] buf = new char[32]; int charPos = 32; int radix = 1 << shift; int mask = radix - 1; do { buf[--charPos] = digits[i & mask]; i >>>= shift; } while (i != 0); return new String(buf, charPos, (32 - charPos)); } The question is, in toUnsignedString, why we create a char arr of 32 chars?

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  • C#: Shift left assignment operator behavior

    - by Austin Salonen
    I'm running code that sometimes yields this: UInt32 current; int left, right; ... //sometimes left == right and no shift occurs current <<= (32 + left - right); //this works current <<= (32 - right); current <<= left; It appears for any value = 32, only the value % 32 is shifted. Is there some "optimization" occurring in the framework?

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  • How is joystick axis information formatted from a USB Joystick?

    - by aquanar
    I actually just have a rather small question, but I have had the HARDEST time finding information about it. For the application I am programming for, there will be a 3-axis joystick being connected via USB to a Windows XP computer, and it is being handled by directx. That information will then be sent elsewhere to an embedded controller. I don't need to know too much of the intricacies of how directx handles it, but I want to know, how is the data for the axes formatted? Nearest I can tell, most joysticks nowadays have 12 bits of resolution, so is the data output as a 12-bit 2's compliment number? And after that, is it represented as a signed 16-bit integer when it is captured from directx? I'd like to know this so I know how I will work with the data at the embedded platform side, such as how to format the packets sending data to the embedded side, as well ashow to use the information once it is on the embedded side.

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  • is mysql index useful on column 'state' when only doing bit-operations on the column?

    - by Geert-Jan
    I have a lot of domain entities (stored in mysql) which undergo lots of different operations. Each operation is executed from a different program. I need to keep (flow)-state for these entities which I implemented in as a long field 'flowstate' used as a bitset. to query mysql for entities which have undergone a certain operation I do something like: select * from entities where state >> 7 & 1 = 1 Indicating bit 7 (cooresponding to operation 7) has run. (<-- simplified) Anyway, I really didn't pay attention to the performance implications of this setup in the beginning, and I think I'm in a bit of trouble since queries as the above run pretty slow. What I'd like to know: Does an mysql index on 'flowstate' help at all? After all it's not a single value Mysql can quickly find using a binary sort or whatever. If it doesn't, are there any other things I could do to speed things up? . Are there special 'mask-indices' for fields with use-cases as the above? TIA, Geert-jan

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  • Get length of bits used in int

    - by sigvardsen
    If you have the binary number 10110 how can I get it to return 11111? e.g a new binary number that sets all bits to 1 after the first 1, there are some likewise examples listed below: 101 should return 111 (3 bit length) 011 should return 11 (2 bit length) 11100 should be return 11111 (5 bit length) 101010101 should return 111111111 (9 bit length) How can this be obtained the easiest way in Java? I could come up with some methods but they are not very "pretty".

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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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