bit-shift

In chapter 2, the section on bitwise operators (section 2.9), I'm having trouble understanding how one of the sample methods works. Here's the method provided: unsigned int getbits(unsigned int x, int p, int n) { return (x >> (p + 1 - n)) & ~(~0 << n); } The idea is that, for the given number x , it will return the n bits starting at position p , counting from the right (with the farthest right bit being position 0). Given the following main() method: int main(void) { int x = 0xF994, p = 4, n = 3; int z = getbits(x, p, n); printf("getbits(%u (%x), %d, %d) = %u (%X)\n", x, x, p, n, z, z);

Before flagging this as a duplicate, please read below, and check my code * my updated code ! So my problem is that, I have to implement Java/JavaScript '>>>' (Unsigned Right Shift / Zero-fill Right Shift), but I can't get it work exactly the same way. I've selected the 11 most promising implementations I've found on SO and on the web (links are added as comments in the code) and added a few test cases. Unfortunately NONE of the functions returned the same response as Java/JS to ALL of the tests. (Maybe some of them are only working on 32bit systems) Live Code + JS+PHP results demo (click Run)

This question already has an answer here: Difference between >>> and >> 7 answers If the shifted number is positive >>> and >> work the same. If the shifted number is negative >>> fills the most significant bits with 1s whereas >> operation shifts filling the MSBs with 0. Is my understanding correct? If the negative numbers are stored with the MSB set to 1 and not the 2s complement way that Java uses the the operators would behave entirely differently, correct? The way negative numbers are represented is called 2's complement. To demonstrate how this works, take -12 as an example. 12, in

1). var bitValue = (byteValue & (1 << bitNumber)) != 0; 2). using System.Collections.BitArray with a Get(int index) method What is faster? In what situations for the .NET projects BitArray could be more useful than a simple conjunction with the bitwise shift? BitArray is going to be able to handle an arbitrary number of boolean values, whereas a byte will hold only 8, int only 32, etc. This is going to be the biggest difference between the two. Also, BitArray implements IEnumerable , where a integral type obviously does not. So it all depends on the requirements of your project; if you need an

I'm a little confused now by java left shift operation, 1<<31 = 0x80000000 --> this I can understand But 1<<32 = 1 Why is this? 1<<33 = 2 Looks like more shifting values, modulus 32 of the value is taken. Thanks everybody for the replying and giving the quote from JLS. I just want to know more. Any idea of the reason why it's designed in this way? Or is it just some convention? Apparently C doesn't have this quirk? Thanks to @paxdiablo. Looks like C declares this behaviour undefined. I have some personal assumption here: ARM architecture Reference Manual A7.1.38 Syntax LSL Rd, Rm, #immed_5

Are shift operations O(1) or O(n) ? Does it make sense that computers generally require more operations to shift 31 places instead of shifting 1 place? Or does it make sense the number of operations required for shifting is constant regardless of how many places we need to shift? PS: wondering if hardware is an appropriate tag.. old_timer Some instruction sets are limited to one bit shift per instruction. And some instruction sets allow you to specify any number of bits to shift in one instruction, which usually takes one clock cycle on modern processors (modern being an intentionally vague

Apple sometimes uses the Bitwise-Shift operator in their enum definitions. For example, in the CGDirectDisplay.h file which is part of Core Graphics: enum { kCGDisplayBeginConfigurationFlag = (1 << 0), kCGDisplayMovedFlag = (1 << 1), kCGDisplaySetMainFlag = (1 << 2), kCGDisplaySetModeFlag = (1 << 3), kCGDisplayAddFlag = (1 << 4), kCGDisplayRemoveFlag = (1 << 5), kCGDisplayEnabledFlag = (1 << 8), kCGDisplayDisabledFlag = (1 << 9), kCGDisplayMirrorFlag = (1 << 10), kCGDisplayUnMirrorFlag = (1 << 11), kCGDisplayDesktopShapeChangedFlag = (1 << 12) }; typedef uint32_t CGDisplayChangeSummaryFlags;

Have you ever had to use bit shifting in real programming projects? Most (if not all) high level languages have shift operators in them, but when would you actually need to use them? Nils Pipenbrinck I still write code for systems that do not have floating point support in hardware. In these systems you need bit-shifting for nearly all your arithmetic. Also you need shifts to generate hashes. Polynomial arithmetic (CRC, Reed-Solomon Codes are the mainstream applications) or uses shifts as well. However, shifts are just used because they are handy and express exactly what the writer intended.