Questions tagged [bitwise-operators]
low-level, primitive operations that directly manipulate bit patterns and binary numerals
57 questions
6
votes
3
answers
636
views
What is the term for a integer variable containing bit fields?
If I have a variable that is intended to to be used with bitmasks, to
retrieve values, i.e. bit fields and flags, what is the academic term
for such a variable?
If the (bit) fields are a analogous to ...
- 192
2
votes
6
answers
667
views
What is the viability of engineering an integral type with values ranging from -1 to 254? Do types like this even exist?
In software engineering, often developers will utilize three different states of a signed integer, as a trilean:
This tends to be quite typical:
-1 - Represents something akin to a null pointer, as in ...
- 3,649
2
votes
2
answers
277
views
Are bitwise operators in C used both for bit operations and for operations for integer or some C types?
In C,
Bitwise logical operators &, |, ^ is used for selecting bits in a word.
Bitwise shifting operators >> and << can be used for implementing multiplication and division between ...
- 5,565
3
votes
5
answers
4k
views
Why is the bitwise AND of 1 and any even number equal to 0?
I’m curious as to why the bitwise AND of any even number with 1 is equal to 0? I’ve looked at the binary representations of an odd number and 1, and have found that the following is always true for ...
- 187
1
vote
2
answers
2k
views
In C++, Why do bitwise operators convert 8 or 16 bit integers to 32 bit?
Is there a logical reason why the integer is upgraded to 32+ bits?
I was trying to make an 8bit mask, and found myself a bit disappointed that the upgrade will corrupt my equations.
sizeof( quint8(0)...
- 3,649
0
votes
1
answer
287
views
How to implement FNV-1(a) in SQLite?
Moved
I originally posted this on SoftwareEngineering because that's where this related question was; but having looked into the Help in detail, I think my question is more on-topic for stackoverflow,...
- 153
4
votes
1
answer
5k
views
Semantics of simulating a 64bit integer with two 32bit integers (hi, lo)
I am working in a system which only supports 32bit integers, in order to have a 64bit (unsigned) integer I decided to simply use two 32bit integers with one being the upper 32 bits (hi), and the other ...
- 143
4
votes
3
answers
809
views
What's the purpose of multiplying by 1024x1024?
I'm working with an old C module that was originally ran on Power PC architecture and compiled with gnu 3.0.6
I'm porting it to run in a VS2012 project on Intel hardware.
The module creates a 3D ...
- 165
-5
votes
5
answers
301
views
Do decimal equivalents to binary number values hold significance in software programming?
It seems as though in software engineering, we care more about these "on and off switch" usages of binary numbers more than the actual values of them numbers... For example, say I have the number:
...
- 1,152
1
vote
2
answers
603
views
C++ - BitVector logic
I have implemented a simple bit vector class. However, I have some problems with understanding, how to push data to it.
In a standard vector, push_back inserts new element et the end. A similar ...
- 141
2
votes
3
answers
732
views
What effects does memory space have on bitwise shifts?
It is true that the bitwise left shift operation (shl) doubles the value of the integer being shifted. However, when constrained to a finite space, such as 8 bits for example, left shift will begin to ...
- 1,152
1
vote
1
answer
389
views
How to understand and design functions with enumeration arguments that work in tandem with bitwise operators in C++ and Qt?
In the C++, there are 6 bitwise operators:
Symbol Operator
& bitwise AND
| bitwise inclusive OR
^ bitwise XOR (eXclusive OR)
<< left shift
>> right shift
~...
- 3,649
1
vote
3
answers
976
views
How can I query, increment & decrement arbitrary-length integers encoded into a bit-array?
I'm in the process of implementing a counting Bloom filter. This data structure is defined as a bit-array and a "width" parameter, W.
The bit array stores unsigned integers, whose size is determined ...
- 2,208
0
votes
1
answer
198
views
Best practices for reading dynamic byte streams: is line-by-line comparison with a mask the best way?
I receive sensor data as a binary stream of bytes. This stream is not always the same length, and does not include the same data set each time. If the sensor did not send a field, it is simply absent, ...
83
votes
7
answers
17k
views
Why are bit masks called "masks" and what purpose do they serve?
Why are "bit masks" called like this?
I know that they are mainly used for bitwise operations and the usage of bit masks is more efficient than the usage of separate variables.
However my question ...
- 2,297
0
votes
1
answer
283
views
Is it possible to store and query combinations of boolean-like information in an integer?
With one boolean, it is simply 0 and 1, and it's straight-forward to query.
With two booleans, it becomes necessary to specify what each number means, ex:
0 F-F
1 F-T
2 T-F
3 T-T
Here it's easy to ...
- 431
2
votes
5
answers
500
views
Shortening a boolean AND with third operand
I'm trying to calculate the sum of 2 bits using basic binary arithmetic and currently, I'm doing this:
function Add(bool a, bool b, bool carry)
{
return
{
Result: a ^ b ^ carry,
...
- 31
40
votes
1
answer
13k
views
Why was the caret used for XOR instead of exponentiation?
Not that it's really a problem for anyone that has faced this syntactic issue before, but I see a wild amount of confusion stemming from the use of the caret (^) as the XOR operation in lieu of the ...
10
votes
2
answers
3k
views
Is it possible to define all bitwise operators using a 'bitwise nand' similar to how all boolean logic can be built using just 'boolean nand'?
Nand is known as a 'universal' logic gate, because it allows you define all other boolean logic gates:
not(x) = nand(x,x)
and(x, y) = not(nand(x, y))
or(x, y) = nand(not(x), not(y))
nor(x, y) = not(...
- 4,947
1
vote
2
answers
223
views
Is there a conceptual 2-bit-input logical operation that does: 0 0 = 0, 0 1 = 1, 1 0 = 0, 1 1 = 0?
Reason: In an LR35902 (the processor in the Game Boy) assembly program of mine, I'm trying to figure out what bits have changed to 1's when comparing A with B, which would need a bitwise operation ...
- 121
4
votes
5
answers
5k
views
How does bitwise information storage in (32-bit) int variables work?
In this book I'm reading I'm going over bitwise operators. Its says the following in the book.
Bitwise operations can potentially store a lot of information in a small amount of memory. Many traits ...
- 185
2
votes
1
answer
3k
views
Getting an array index (0,1,2,..8) from bit masking value (1,2,4,8..256) without using log2(n). Maybe a design issue
I'm working on a component where I put in data and I get different data as a result. The input is always the same (3 Objects).
From these 3 Objects up to 9 other Objects can be calculated. One ...
- 167
1
vote
2
answers
869
views
LSB-propagating left shift, conceptual equivalent of sign-propagating right shift [closed]
How would I write something that fills with the right-most bit (<<< is used to denote this non-existent operator):
1 <<< 7: "11111111" and 0 <<< 7: "00000000"
9 <<&...
- 121
0
votes
1
answer
515
views
How to calculate big O notation according to number width?
I'm trying to understand big O with the bitwise operations. I have 2 functions those are solving the same question from different perspective.
num1BitsSecondSolution starts to shift the number right ...
- 469
3
votes
3
answers
341
views
Is there any low level way to get shifted or unshifted bits which results from bitwise operations?
I was playing with bitwise operations and a question about counting true bits of any positive integer value, so I solved the problem with bit shifting, so I just thought if there would be some way to ...
- 469
1
vote
3
answers
3k
views
Bits - Least-Significant/Lowest is 0th or 1st; zero or one indexed
Question
Is there a rough consensus if the bitmask 0x01 is properly said to have the "zeroth" bit set, or the "first" bit set?
If there isn't rough consensus that there's a generally right answer, ...
- 269
3
votes
1
answer
875
views
Overflow Exception Checking Problem
Background
I have to call a method that needs to return a signed integer (see code block below) after converting from an unsigned integer. The reason for this is that I have to do bit-wise math that ...
- 2,758
0
votes
1
answer
1k
views
Is there a way to do bitwise operation with more than two state
I know how make bit operation. I'm wondering if you need more than 2 states is there a way to do it using bit instead of array and % operators. Because those are really slow.
So in case the array ...
27
votes
2
answers
26k
views
Is there any advantage to c-style bit manipulation over std::bitset?
I work almost exclusively in C++11/14, and usually cringe when I see code like this:
std::int64_t mArray;
mArray |= someMask << 1;
This is just an example; I'm talking about bit-wise ...
- 1,386
3
votes
1
answer
973
views
How do you set and check a single bit in a programming language that does not support bitwise operations?
I'm using a programming language (more a scripting language) that does not support any bitwise operators like AND, OR, XOR, NOT (and shift as well).
Common arithmetic and logical operations like + - *...
- 279
0
votes
2
answers
4k
views
boolean operations in C using bitfields
I am trying to implement boolean data type in C. Basically, I am working with sets.
The following code can be used to access each bit but I am unsure whether I can represent sets using this method.
...
- 135
29
votes
11
answers
12k
views
When I test out the difference in time between shifting and multiplying in C, there is no difference. Why?
I have been taught that shifting in binary is much more efficient than multiplying by 2^k. So I wanted to experiment, and I used the following code to test this out:
#include <time.h>
#include &...
- 399
11
votes
3
answers
52k
views
What does "(int) value & 0x1, (int) value & 0x2, (int) value & 0x4, (int) value & 0x8" mean?"
The "value" ranges from 0 to 15 (its possible values). When will those 4 "if" conditions be met? If my (int)value = 2 does this mean 0010?
if ((int)value & 0x1)
{
...
patr
9
votes
3
answers
3k
views
In Java, why use bit hacks when non-bitwise technique it is more readable?
Is there any legitimate use for bit manipulation hacks in higher-level languages such as Java?
I can see them being useful in speed-sensitive low-level and computation-intensive programs, e.g. ...
- 306
2
votes
2
answers
224
views
gcc -S seems a bit misshapen with shifting and ANDing bits
Example:
int c = 4;
int p = 5;
if (p & (1 << c))
printf("ok\n");
else
printf("nop\n");
gcc -S:
movl -4(%rbp), %eax /* eax holds the variable c */
movl -8(%rbp), %edx /* ...
- 123
19
votes
4
answers
96k
views
How are negative signed values stored?
I was watching this video on the maximum and minimum values of signed integers.
Take an example of a positive signed value - 0000 0001
The first bit denotes that the number is positive and the last ...
- 319
0
votes
1
answer
162
views
Why Num&sizeMinusOne faster than num&(size-1)
I've been told that when I have a hash table of size m and m=2^k, I can use the & operator as num & (size-1) instead of num % size, to fit the hashCode to my table size.
I've also been told ...
- 101
14
votes
3
answers
43k
views
Speeds of << >> multiplication and division
You can use << to multiply and >> to divide numbers in python when I time them I find using the binary shift way of doing it is 10x faster than dividing or multiplying the regular way.
...
- 327
6
votes
4
answers
6k
views
Why do higher level languages have neither xor nor nand short-circuit operators?
While many higher level languages have bitwise (exclusive or) and bitwise (exclusive and), for instance C, C++, Java, etc. I'm curious why the ( vastly more useful ) logical short-circuit operators ...
- 179
5
votes
2
answers
2k
views
Why is ~0 a Sequence of 1s [closed]
Why is ~0 a sequence of 1 bits and not just a single bit? Where do the extra 1 bits come from? Does this mean ~1 a sequence of 0 bits or just a single 0 bit?
My understanding was that the ~ operator ...
- 193
2
votes
1
answer
1k
views
Next power of 2 for a number (in search for better "bit-twiddling" way)
I just wonder if there exists better (i.e. faster?) way to get the next
power of 2 for a given number than the following one (maybe some
better sort of "bit-twiddling" hack is possible?) ...
static ...
- 151
5
votes
1
answer
7k
views
Clearing the lowest set bit of a number
I can see in this tutorial on bit manipulation, under the heading "Extracting every last bit", that -
Suppose we wish to find the lowest set bit of x (which is known to be
non-zero). If we ...
- 153
0
votes
3
answers
761
views
Using Power of 2 numbers to represent types
Let's say that we have some values, represented by power of 2:
TYPE_1 = 1
TYPE_2 = 2
TYPE_3 = 4
TYPE_4 = 8
...
I need to store some of these types in one value.
Example:
To represent TYPE_1 with ...
- 1,077
4
votes
2
answers
2k
views
Concept of bit fields
Whenever I read a code like this:
struct node
{
int x : 2;
int p : 4;
}n;
with bit fields involved, I get really confused, as to how they are represented in memory, what is ...
- 1,319
75
votes
2
answers
9k
views
Why do bitwise operators have lower priority than comparisons?
Could someone explain the rationale, why in a bunch of most popular languages (see note below) comparison operators (==, !=, <, >, <=, >=) have higher priority than bitwise operators (&, |, ^...
- 5,236
77
votes
8
answers
110k
views
Using scoped enums for bit flags in C++
An enum X : int (C#) or enum class X : int (C++11) is a type that has a hidden inner field of int that can hold any value. In addition, a number of predefined constants of X are defined on the enum. ...
- 2,755
3
votes
2
answers
2k
views
What kind of specific projects can I do to master bitwise operations in C++? Also is there a canonical book? [closed]
I don't use C++ or bitwise operations at my current job but I'm thinking of applying to companies where it is a requirement to be fluent with them (on their tests anyway).
So my question is: Can ...
- 439
17
votes
3
answers
66k
views
Is there something special about the number 65535?
2¹⁶-1 & 2⁵ = 2⁵ (or? obviously ?)
A developer asked me today what is bitwise 65535 & 32 i.e. 2¹⁶-1 & 2⁵ = ?
I thought at first spontaneously 32 but it seemed to easy whereupon I thought ...
- 8,198
8
votes
4
answers
29k
views
Ternary operator (condition ? foo : bar) and the XOR (^) operator
I have read in a recent code review that both ternary operator (condition ? foo : bar) and the XOR operator ^ are rarely used in Java. Is it true?
If yes, is this because they are less readable? or ...
- 183
0
votes
2
answers
19k
views
Flipping the desired bit of an integer number [duplicate]
Suppose you were given an integer number in decimal notation. This when represented in binary will be a series of 0's and 1's. This sequence varies in length with the magnitude of the number. Now ...
- 307