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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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  • 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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  • 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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  • 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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  • 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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  • Why does the right-shift operator produce a zero instead of a one?

    - by mrt181
    Hi, i am teaching myself java and i work through the exercises in Thinking in Java. On page 116, exercise 11, you should right-shift an integer through all its binary positions and display each position with Integer.toBinaryString. public static void main(String[] args) { int i = 8; System.out.println(Integer.toBinaryString(i)); int maxIterations = Integer.toBinaryString(i).length(); int j; for (j = 1; j < maxIterations; j++) { i >>= 1; System.out.println(Integer.toBinaryString(i)); } In the solution guide the output looks like this: 1000 1100 1110 1111 When i run this code i get this: 1000 100 10 1 What is going on here. Are the digits cut off? I am using jdk1.6.0_20 64bit. The book uses jdk1.5 32bit.

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  • Proper way to handle issue when porting 32 to 64 bit. Conversion from DT1 to DT2 of greater size

    - by grobartn
    So I am trying to port 32 bit to 64 bit. I have turned on the VS2008 flag for detecting problems with 64 bit. I am trying following: char * pList = (char *)uiTmp); warning C4312: 'type cast' : conversion from 'unsigned int' to 'char *' of greater size Disregard the code itself. This is also true for any pointer, because 64 bit pointer is greater than 32 bit unsigned int or int for that purpose. Given that you have to cast smaller type to greater how would you go about doing it so it correctly on both 32/64 bit systems

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  • Overwriting a range of bits in an integer in a generic way

    - by porgarmingduod
    Given two integers X and Y, I want to overwrite bits at position P to P+N. Example: int x = 0xAAAA; // 0b1010101010101010 int y = 0x0C30; // 0b0000110000110000 int result = 0xAC3A; // 0b1010110000111010 Does this procedure have a name? If I have masks, the operation is easy enough: int mask_x = 0xF00F; // 0b1111000000001111 int mask_y = 0x0FF0; // 0b0000111111110000 int result = (x & mask_x) | (y & mask_y); What I can't quite figure out is how to write it in a generic way, such as in the following generic C++ function: template<typename IntType> IntType OverwriteBits(IntType dst, IntType src, int pos, int len) { // If: // dst = 0xAAAA; // 0b1010101010101010 // src = 0x0C30; // 0b0000110000110000 // pos = 4 ^ // len = 8 ^------- // Then: // result = 0xAC3A; // 0b1010110000111010 } The problem is that I cannot figure out how to make the masks properly when all the variables, including the width of the integer, is variable. Does anyone know how to write the above function properly?

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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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  • How do I unpack bits from a structure's stream_data in c code?

    - by Chelp
    Ex. typedef struct { bool streamValid; dword dateTime; dword timeStamp; stream_data[800]; } RadioDataA; Ex. Where stream_data[800] contains: **Variable** **Length (in bits)** packetID 8 packetL 8 versionMajor 4 versionMinor 4 radioID 8 etc.. I need to write: void unpackData(radioDataA *streamData, MA_DataA *maData) { //unpack streamData (from above) & put some of the data into maData //How do I read in bits of data? I know it's by groups of 8 but I don't understand how. //MAData is also a struct. }

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  • Getting the fractional part of a float without using modf()

    - by knight666
    Hi, I'm developing for a platform without a math library, so I need to build my own tools. My current way of getting the fraction is to convert the float to fixed point (multiply with (float)0xFFFF, cast to int), get only the lower part (mask with 0xFFFF) and convert it back to a float again. However, the imprecision is killing me. I'm using my Frac() and InvFrac() functions to draw an anti-aliased line. Using modf I get a perfectly smooth line. With my own method pixels start jumping around due to precision loss. This is my code: const float fp_amount = (float)(0xFFFF); const float fp_amount_inv = 1.f / fp_amount; inline float Frac(float a_X) { return ((int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } inline float Frac(float a_X) { return (0xFFFF - (int)(a_X * fp_amount) & 0xFFFF) * fp_amount_inv; } Thanks in advance!

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  • Rotating bits of any integer in C

    - by Tim
    Pass a integer 2 to this function and then return a integer which is 4 x = 2; x = rotateInt('L', x, 1); (left shift the bits by 1) Example: 00000010 - rotate left by 1 - 00000100 but if I pass this: x = rotateInt('R', x, 3); it will return 64, 01000000 Here is the code, can someone correct the error... thanks int rotateInt(char direction, unsigned int x, int y) { unsigned int mask = 0; int num = 0, result = 0; int i; for(i = 0; i < y; i++) { if(direction == 'R') { if((x & 1) == 1) x = (x ^ 129); else x = x >> 1; } else if(direction == 'L') { if((x & 128) == 1) x = (x ^ 129); else x = x << 1; } } result = (result ^ x); return result; }

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  • How to tell if Microsoft Works is 32 or 64 bit? Please Help!

    - by Bill Campbell
    Hi, I am trying to convert one of our apps to run on Win7 64 bit from XP 32 bit. One of the things that it uses is Excel to import files. It's a little complicated since it was using Microsoft.Jet.OLEDB.4.0 (Excel). I found Office 14 (2010) has a 64bit version I can download. I downloaded Office 2010 Beta but it didn't seem to install Microsoft.ACE.OLEDB.14.0. I found that I could download 2010 Office System Driver Beta: Data Connectivity Components which has the ACE.OLEDB.14 in it but when I try to install it, the installed tells me "You cannot install the 64-bit version of Access Database engine for Microsoft Office 2010 because you currently have 32-bit Office products installed". How do I determine what 32bit office products this is reffering to? My Dell came with Microsoft Works installed. I don't know if this is 32 or 64 bit. Is there anyway to tell? I don't want to uninstall this if it's not the problem and I'm not sure what else might be the problem. Any help would be appreciated! thanks, Bill

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  • How do I know my laptop is 64 bit compatible?

    - by c.sokun
    I recently plan to buy a new laptop to run 64 bit OS, but I friend told me that my current laptop is 64 bit but I am not sure how do I verify if my laptop is ready to load 64 bit OS? Here is the result from cpuz edit: come say something at less if you want to vote this down :)

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  • Can I run virtualized 64-bit Operating Systems if my CPU doesn't support VT-X?

    - by tintinmj
    I have installed VMWare 10.0 workstation on my Compaq CQ60-615DX laptop. The Operating System is Windows 7 Home Premium. When I tried to run Ubuntu 14.04 64-bit in a virtual machine in VMWare I get an error saying: This virtual machine is configured for 64-bit guest operating systems. However, 64-bit operation is not possible. This host does not support Intel VT-x. For more detailed information, see http://vmware.com/info?id=152. So I googled and found that I have to enable Intel VT-x. But I found out that my processor doesn't support Intel® Virtualization Technology (VT-x). So am I doomed and can I never run any virtual OS on my laptop? Or can I run 32-bit OSes?

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  • How can install scripts determine which are the correct equivalents for /usr/lib for 32- and 64-bit libraries?

    - by Randalli
    I have an SDK that must install 32-bit and 64-bit files in the correct places under /usr/lib for a variety of Linux distributions. For example, it appears that for Fedora, /usr/lib64 is the 64bit lib, but for Debian based systems, /usr/lib is the 64bit directory. I want to find out if there is a reliable way to determine the correct locations. More specifically, is there a way an install script can determine programmatically which are the correct equivalents for /usr/lib for 32- and 64-bit libraries on a given distribution?

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