Bitwise Logic
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Strictly speaking, bit strings are not nearly as easy to understand as named boolean variables; but there are situations when they can simplify or eliminate the need for long boolean expressions. Consider my recent post about the ShortcutManager . There are three control keys that may or may not be pressed at any given time. This amounts to 8 possible key combinations (7 if you ignore when none of them are pressed). Here’s what this would look like if you used a boolean expression to check for each of the possible combinations: That might not seem too bad, and it isn’t that hard to understand what’s going on (even without the comments).
Using Bit-wise Math to Simplify Logic -
Tutorials - Bitwise Operators and Bit Manipulations in C and C
Generally, as a programmer you don't need to concern yourself about operations at the bit level. You're free to think in bytes, or ints and doubles, or even higher level data types composed of a combination of these. But there are times when you'd like to be able to go to the level of an individual bit. Exclusive-or encryption is one example when you need bitwise operations.
C# Logical Bitwise Operators :: BlackWasp Software Development
The ninth part of the C# Fundamentals tutorial extends upon the previous article dealing with C# Boolean operators. Boolean operations may also be carried out on integer representations of binary numbers. This article considers logical bitwise operators. In the previous part of the C# Fundamentals tutorial I described the Boolean operators and their effect on Boolean values. The bitwise logic operators provide the same logical AND , OR and XOR functions for operation on each bit of integer values.
Bitwise operations are operations that act on numbers at the bit level. Although bitwise operations have many potential uses for storing one bit and manipulating numbers, the most frequent use at ITP is probably to interface with a shift register and control many more LEDs than you would be able to if using one digital pin for each LED. Binary Before working with bitwise operators, it's important to understand binary numbers. A binary number is just a number in which each digit represents a power of 2 (as opposed to decimal where each digit represents a power of 10). Sometimes binary numbers will be indicated in code with a zero and a lower-case 'b' before the number, e.g. 0b1001 or 0b001011, but the standard implementation in Arduino is to use a capital 'B' before the number, e.g.
Bitwise Math - ITPedia
Double bitwise NOT (~~)
The bitwise NOT operator ( ~ ) will take its operand, convert it to a 32-bit integer, and will invert each bit so that each 0 becomes a 1 and vice versa. 00000000000000000000000000001001 ...becomes 11111111111111111111111111110110 The effect of this, given the expression ~foo is -(foo + 1) . A double bitwise NOT operation ( ~~foo ) will therefore result in -(-(foo + 1) + 1) . This only remains true for integers though; given all the potential operands, the real equivalent expression to ~~ is probably something like:
Bit Twiddling Hacks
Individually, the code snippets here are in the public domain (unless otherwise noted) — feel free to use them however you please. The aggregate collection and descriptions are © 1997-2005 Sean Eron Anderson. The code and descriptions are distributed in the hope that they will be useful, but WITHOUT ANY WARRANTY and without even the implied warranty of merchantability or fitness for a particular purpose. As of May 5, 2005, all the code has been tested thoroughly.
Bitwise Operations in C
Introduction After writing the Game Programming Genesis series , I got a lot of E-mail from people asking me to clarify the bitwise operations I used in the sample programs. I use them all over the place in my code, enough that I don't really think about what I'm writing anymore, and so I neglected the fact that a lot of people don't see them used too often. This article is meant to be a complete introduction to bitwise manipulations using the C programming language. If you don't know C, no big deal.
labs » Bitwise gems – fast integer math
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Introduction This article demonstrates a simple use of bit fields as flags for Windows forms. Bit fields allow packaging of data into simple structures, and they are particularly useful when bandwidth, memory or data storage is at a premium. This might not appear to be an issue with modern day equipment or every day applications, but we can save up to 16 times more memory and storage when using bit fields instead of other value types such as boolean.
Masks and flags using bit fields in .NET - CodeProject
This works because one bit in an integer is used as the sign bit (1 indicates negative). The and operation (a & b) will be a meaningless number, but its sign will be the bitwise and of the signs of the numbers and hence checking the sign of the result will work. This may or may not benefit performance. Doing two boolean tests/branches will be worse on a number of architectures and compilers. Modern x86 compilers can probably generate a single branch using a some of the newer instruction even with the normal syntax. As always, if it does result in a performance increase...