1

not a native programmer here (medical background). I am looking for a bitwise operator that gives me the following results given the following conditions. The programming language is Python but that should not be too relevant:

condition1 condition2 result
0          1          0
1          1          1
1          0          1
0          0          1

Is this achievable with one operator alone? How would the code look like? I know it can be achieved with if/else statements but am interested in understanding new fields of programming.

Jan
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    Best I can think of is `~(condition1 ^ condition2) | condition1` – 0x5453 Jul 30 '20 at 16:05
  • @0x5453: Thanks. How would that work? – Jan Jul 30 '20 at 16:05
  • For this example, `condition1 ^ condition2` would evaluate to `1010`. `~` flips that to `0101`, then the `| condition1` fixes the third case to `0111`. – 0x5453 Jul 30 '20 at 16:07
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    Your bio says "I do have 20+ years experience in programming, mainly in C, C++, PHP and Python with a bit of MySQL and JavaScript as well". I think you can safely call yourself a programmer. – Pranav Hosangadi Jul 30 '20 at 16:08
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    It's everything except the first case `~condition1 & condition2`. So it's `condition1 | ~condition2`. – khelwood Jul 30 '20 at 16:08
  • @PranavHosangadi: Of course I am and I have a lot of experience. But I do not have a *theoretical* background, that is I do not know what an automata state machine is or deMorgan's rules. Simply because I did not study it but learned it on the way. – Jan Jul 30 '20 at 18:20
  • @khelwood: Mind posting an answer? – Jan Jul 30 '20 at 18:21
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    @Jan Certainly. – khelwood Jul 30 '20 at 18:22

3 Answers3

3

Your expected result is 1 for every case except the first.

The first case (where condition1 is 0 and condition2 is 1) is described by ~condition1 & condition2.

The opposite of that expression is

condition1 | ~condition2

so this expression gives the expected result for every case.

As requested, some detail on the difference between logical boolean operations and bitwise operations.

If we have two boolean values A and B, and we want to perform an "or" operation on them, we use the Python operator or and we get back one boolean value.

If we have two integers A and B, and we want to perform a bitwise "or" operation on them, we use the Python operator | and we get back an int whose bits are determined by the operation's action on each bit in A and B.

For instance

If A is 12 and B is 5, then they have the following bits:

A   = 1100
B   = 0101
A|B = 1101

In this case, the result A|B is 1101 binary, which is 13 decimal.

With the bitwise "not" operator the result is a little more complex to understand.

The binary representation of the number 1 is that the smallest bit is 1 and all the other bits are zero. So when you perform ~1, you don't get zero. You get a number whose every bit is 1 except for the smallest, which is zero.

 1 = 00...001
~1 = 11...110

Because ints are stored in two's complement, 11...110 is the binary representation of the number -2.

So though the boolean not operator gives you not 1==0 (i.e. not True==False), the bitwise ~ operator gives you ~1 == -2, since every individual bit gets flipped.

khelwood
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1

You could use condition1**condition2

>>> 0**1
0
>>> 1**1
1
>>> 1**0
1
>>> 0**0
1

or more generally condition1 OR (NOT condition2)

abc
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1

this is clearly not (not A and B)
usind De Morgan A or not B
In bitwise meaning A | ~B

| is or, ~ is invert (not)

Superior
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