Bitwise XOR operator to replace bitwise NOT operator?

[Osmany_Ferrer_Borges]

Hi,
I need to invert the bits of an integer but I can't find the bitwise NOT operator.

I am trying the following alternative to get inverted the 28 lower bits.

Is this a valid alternative?

Thanks,
Osmany

[nishyanthkumar]

Now that I realize, you could just subtract the number from a string of just 1s ((10^n)-1/9).

[ABG]

Do we have to worry about the integer being negative?

[ABG]

Here's some sample conversion code for you.
Note that AI2 binary 1 and 0 are text unless working with bitwise operators.

计算CRC校验码 Calculate CRC check code

Here's a draggable block you can use in AI2: [IEEE_754_Float] It has loads of bit manipulation in it. Attribution: by flodmotorgrodan@gmail.com at The rest of the project: [1_5] [5_5] [128] [Designer] [when btnAbout .Click do] IEEE754.aia (5.2 KB) [to IEEE_754_Float IEEE_754_Int32 result] [to lpad text pad len result] [when btnHexToDec .Click do] [when btnBinToDec .Click do] [when btnConvertDecBinary32 .Click do] [when btnDecToBin .Click do]

[Osmany_Ferrer_Borges]

Hi @ABG,

I was asking for validation because I don't know the internal representation of numbers in appinventor.

I am representing sets using bits of integers. The universe of elements are the numbers from 0 to 27. If, for example, bits 0 and 10 of an integer (representing a set) are active (0x00000401 as hexadecimal, 1025 as decimal), then the set is {0, 10}.

The complement of that set would be the bitwise NOT operator, it should be the set {0...27} - {0,10} which as a number would be (0xFFFFFBFE as hexadecimal, -1026 as decimal).

As you can see here, number could result negative.

I require the best possible performance, working with strings is not an option, nor with lists. Rewriting my example without using strings

where the value 268435455 is 0x0FFFFFFF in hex.

Thanks @nishyanthkumar, i've rewrote my code as procedure to invert lower 28 bits. This operator works for that amount of bits.

BEST REGARDS,
Osmany

[ABG]

@Osmany_Ferrer_Borges

I require the best possible performance

This is how far you are from bare metal:

Strings, numbers, what size can they have?

I’ll address the question in three parts as the actual answer is somewhat complicated. In particular, it’s important to know that at the core of App Inventor is an implementation of the Scheme language called Kawa. Theoretical String Length There are two different internal string types in App Inventor. Kawa provides a mutable string type called FString and then there’s Java’s standard String type. Conversions are done from FString to String on an as needed basis to interact with the parts of th…

from

FAQ section: Maths

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[Osmany_Ferrer_Borges]

Thanks @ABG,

I had already read that post, it doesn't say how many bits long an integer is, that way I could know what number I do an XOR with, so my alternative works in a general way.

Maybe @ewpatton could help why AppInventor doesn't provide the bitwiseNOT operator and and what alternative to use.

Thanks for your time,
Osmany

[ewpatton]

@Osmany_Ferrer_Borges

Maybe @ewpatton could help why AppInventor doesn't provide the bitwiseNOT operator and and what alternative to use.

Someone could certainly implement one as Scheme provides a bitwise-not function over its IntNum type.

Since the negation block performs two's complement on the number, you should be able to do bitwise negation on integers using the following:

[Osmany_Ferrer_Borges]

Thank you very much @ewpatton,

That works very well. The inclusion of this operator should be proposed.
Best regards.
Osmany

[ABG]

But how many 1's are there in bitwisenot(0)?

[Osmany_Ferrer_Borges]

Hi @ABG,
That's the question.... How many bits long is an integer?
As many bits as the representation of the integer -1 needs or supports.
Maybe this is why bitwise-NOT operator is not implemented.

In my case I'm only analyzing the lower 28 bits, and the solution from @ewpatton works well.