Most frequently used bitwise operators.

[sandras]

From your experience, what are the most frequently used bitwise operators, when not dealing with hardware?

[Kazinsal]

AND and OR. Bitwise NOT is also up there. The only time I use XOR often is as a replacement for mov reg, 0.

[Combuster]

Probably AND at the top. The typical OR construct has competition from a substitute writing: optionflag1+optionflag2+optionflag3

I think shifts beat bitwise NOT. Especially since they make good divides/multiplies and the compiler knows that.

[dozniak]

BSR/BSL might be used for implementing bitmaps in e.g. memory manager in a very handy way on x86.

[benjii]

Uhm, probably AND, but I always use XOR when nulling something .

[Mikemk]

signed shift when multiplying/dividing by powers of two

[bewing]

OR for adding bitflags to bitfields. AND for masking and testing flagbits. XOR for toggling bitflags on and off. Left shifts for indexing arrays of various sizes (and the occasional "multiply by 2"). I use them all lots. The ones I almost never use are NOT and rotations.

[Mikemk]

NOT is useful for reversing byte sized boolean values that most operating systems and higher level languages foolishly waste your ram with.

[Love4Boobies]

Depends on what the problem is. E.g.:

• For cryptography, XOR
• For bit flags and masks, AND/OR
• For array indexing, shifting
• For logic gates, NAND
• For serialization, AND/shifting (for encoding, see Combuster's point on OR)
• etc.

Why the survey?

[Mikemk]

• For logic gates, NAND

Umm... aren't all bitwise operators a type of logic gate?

[iansjack]

• For logic gates, NAND

Umm... aren't all bitwise operators a type of logic gate?

No.

A logic gate normally refers to a circuit with one or more binary inputs and a single binary output. Clearly

13 & 5

(for example) does not fulfil these conditions. Logical operators, on the other hand, do; for example:

13 && 5

[Mikemk]

13 & 5 performs:

Code: Select all

  1101
& 0101
------
  0101

You are right. It's not a logic gate - it's [in this case] 4 gates.

[Love4Boobies]

Umm... aren't all bitwise operators a type of logic gate?

No. An operator is a mathematical function. For example, in the case of Boolean, there are 2^2^n operators that can be applied to an n-bit string (NAND is one of the 16 operators that can be applied on bit operand pairs and, because we are talking bitwise, we actually apply NAND to every corresponding bit pair individually). On the other hand, a logic gate is a physical device that implements a Boolean function. I hope you see the difference since it's a bit like confusing apples and arithmetic because you were taught the latter using the former.

Also, I think you missed my point. Most of the logic gates inside digital computers are actually NAND gates, which are cheaper and sometimes slower but on top of which all other constructs can be built.

[Owen]

Most of the logic gates inside digital computers are actually NAND gates, which are cheaper and sometimes slower but on top of which all other constructs can be built.

While the NAND or NOR gate can be used to construct all other logic gates... nobody actually does this

[Love4Boobies]

No? I don't know where I got that from; I should take one of Coursera's courses on these matters. In that case, I don't know what the most common operation is when working with logic gates or whether one can be singled out.