Ones' Complement of Not 0 - Not quite technically correct?

General
1

Hi Everyone,

I am doing some work with MemoryBlocks and integers, and am getting different results from ‘Not 0’ when I use a MemoryBlock or when using an integer. Not zero in an integer of 1 is zero, while Not Zero of a memoryblock is 1111111111111111111111111111111111111111111111111111111111111110.

I understand that the One’s complement of the memory block should be 1111…etc…1111, and the last digit should probably be a 1 instead of a zero to have the number -0… am I correct, or did I mess up some code?.. :slight_smile:

Here is the code for using not 1 with an integer:

[code]Sub Action() Handles Action
//Create 2 integer variables
Dim X, Z as Integer
//Populate X with binary text data
X = Val("&b" + TFX.Text)

//Calculate Bit AND result
Z = Not X

//Show Bit Not result
LblAnswer.Text = Z.ToBinary
End Sub
[/code]

Here is the code for using not 1 with a MemoryBlock:

[code]Sub Action() Handles Action
//Create a MemoryBlock Variable
//64 bytes * 8 bits/byte = 512
Dim X as New MemoryBlock(512)

//Populate X with binary text data
X.UInt64Value(0) = Val("&b" + TFX.Text)

//Calculate Bit XOR result
Dim Z as New MemoryBlock(512)
Z.UInt64Value(0) = Not X.UInt64Value(0)

//Show Bit XOR result
LblAnswer.Text = Z.UInt64Value(0).ToBinary
End Sub
[/code]

The program can be downloaded here:

Example2-4.xojo_binary_project

2

Instinctively, Id say both these responses are wrong, although I can see how you might defend
Not 0 == 1

If doing a true NOT at a bit level,
Not 0 should get you a string of 1s as wide as the integer storage
So at bit level, you get 1
At byte level you get 11111111
and so on… but everything that was 0 should be 1

3

Yes, I agree Jeff. Glad to see that what I wrote made sense :slight_smile:

I’ll file a feedback report.

4

<https://xojo.com/issue/49007>

5

Mind you…the comments are a little bit misleading :slight_smile:

//Calculate Bit AND result
//Show Bit XOR result

6

Your right that the comments were misleading. I was calculating NOR and AND to make sure that those functions worked and I forgot to update the comments. Thanks for mentioning it.

7

You need to enforce 64bit by using UInt64 instead of using Integer. Then the results are identical. So no bug.

8

Here is the code:

Dim x As UInt64 = Val("&b" +TFX.Text) Dim z As UInt64 = Not x LblAnswer1.Text = z.ToBinary(64)
and:

[code]Dim x As New MemoryBlock(512)
x.UInt64Value(0) = Val("&b" +TFX.Text)

Dim z As New MemoryBlock(512)
z.UInt64Value(0) = Not x.UInt64Value(0)

LblAnswer.Text = z.UInt64Value(0).ToBinary(64)[/code]

9

Good to know, if slightly overcomplicated.
On a 64bit build, Integer should be 64bit anyway, yes?

10 house points to Eli

10

???

Yes. But this project is set to 32-bit.

11

Many thanks to @Eli Ott and @Robin Lauryssen-Mitchell as they both had the same answer.

I didn’t know that the value of 64 could be added to the ToBinary extension:

LblAnswer.Text = z.UInt64Value(0).ToBinary(64)

I always seem to be learning something new :slight_smile:

12

Just an added note for the logic clarity behind this question. I made a presumption in believing that because the integer value of ‘not 1 = 0’, then the binary value of 'not 0001 should mistakenly be ‘0000’ (binary representation of an integer), and instead the program correctly had the value of ‘not 0001 is 1110’