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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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  • 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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