Bitwis com

In digital computer programminga bitwise operation operates on one or more bit patterns or binary numerals at the level of their individual bits.

It is a fast, simple action directly supported by the processorand is used to manipulate values for comparisons and calculations. On simple low-cost processors, typically, bitwise operations are substantially faster than division, several times faster than com, and sometimes significantly faster than addition. While modern processors usually perform addition and multiplication just as fast as bitwise operations due to their longer instruction pipelines com other architectural design choices, bitwise operations do commonly use less power because of the reduced use of resources.

For example, the binary value decimal 1 has zeroes at every position but the first one. Bits that are 0 become 1, and those that are 1 become 0. A simple but illustrative example use is to invert a grayscale image where each pixel is stored as an unsigned integer. A bitwise AND takes two equal-length binary representations and performs the logical AND operation on each pair of the corresponding bits, by multiplying them.

This is often called bit masking. By analogy, the use of masking tape covers, or masksportions that should not be altered or portions that are not of interest. In this case, the 0 values mask the bits that are not of interest. The bitwise AND may be used to clear selected bits or flags of a register in which each bit represents an individual Boolean state. This technique is an efficient way to store a number of Boolean values using as little memory as possible.

A bitwise OR takes two bit patterns of equal length and performs the logical inclusive OR operation bitwis each pair of corresponding bits. The result in each position bitwis 0 if both bits are 0, while otherwise the result is 1. The result in each position is 1 if only the first bit is 1 or only the second bit is 1, but will be 0 if both are 0 or both are 1.

In this we perform the comparison of two bits, being 1 if the two bitwis are different, and 0 if they are the same. Any bit may be toggled by XORing it with 1. Assembly language programmers sometimes use XOR as a short-cut to setting the value of a register to zero. Performing XOR on a value against itself always yields zero, and on many architectures this operation requires fewer clock cycles and memory than loading a zero value and saving it to the register. In these operations the digits are moved, or shiftedto the left or right.

Registers in a computer processor have a fixed width, so some bits will be "shifted out" of the register at one end, while the same number of bits are "shifted in" from the other end; the differences between bit shift operators lie in how they determine the values of the shifted-in bits.

In an arithmetic shiftthe bits that are shifted out of either end are discarded. This statement is not reliable in the latest C language draft standard, however.

If the value being shifted is negative, the result is "implementation-defined," indicating the result is not necessarily consistent across platforms. In the second case, the rightmost 1 was shifted out perhaps into the carry flagand a new 1 was copied into the leftmost com, preserving the sign of the number but not reliably, according to the most recent C language draft standard, as noted above.

Com shifts are sometimes shortened to a single shift by some number com digits. In a logical shiftzeros are shifted in to replace the discarded bits. Therefore, the logical and arithmetic left-shifts are exactly the same.

Another form of bitwis is the circular shift or bit rotation. In this operation, the bits are "rotated" as if the left and right ends of the register were joined. The value that is shifted in on the right during a left-shift is whatever value was shifted out on the left, and vice versa. This operation is useful if it is necessary to retain all the existing bits, and is frequently used in digital cryptography. Rotate through carry is similar to the rotate no carry operation, but the two ends of the register are separated by the bitwis flag.

The bit that is shifted in on either end is the old value of the carry flag, and the bit that is shifted out on the com end becomes the new value of the carry flag. A single rotate through carry can simulate a logical or arithmetic shift of one position by setting up the carry flag beforehand.

For example, if the carry flag contains 0, then x RIGHT-ROTATE-THROUGH-CARRY-BY-ONE is a logical right-shift, and if the carry flag contains a copy of the sign bit, then x RIGHT-ROTATE-THROUGH-CARRY-BY-ONE is an arithmetic right-shift. With rotate-through-carry, that bit is "saved" in the carry flag during the first shift, ready to shift in during the second shift without any extra preparation. The number bitwis places to shift is given as the second argument to the shift operators.

Shifts com result in implementation-defined behavior or undefined behaviorso care must be taken when using them. If the first operand is of type uint or ulong, the right-shift is a logical shift. Care must be taken to ensure the statement is well formed to avoid undefined behavior and timing attacks in software bitwis security requirements.

However, the branch adds an additional code path and presents an opportunity for timing analysis and attack, which is often not acceptable in high integrity software. To avoid the undefined behavior and branches under GCC and Clang, the following should be used. Intel also provides x86 Intrinsics. The number of places to shift is given as the second argument. Although machines often have efficient built-in instructions for performing arithmetic and logical operations, all these operations can be performed by combining the bitwise operators and zero-testing in various ways.

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