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JohnOne

bitwise calcs

8 posts in this topic

#1 ·  Posted (edited)

I wonder if anyone could help me understand how to use them/ how they work

I never even heard of then before landing on this forum :mellow:

I'll give an example using these flags

1

2

4

8

16

32

64

If I have the number 44, how do I use the bitwise functions to decide what flags are used to arrive at that number.

It looks like binary and Im one of the 0 people who understands it.

Help much appreciated.

Edited by JohnOne

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If BitAND(44, 1) Then 1 is used

If BitAND(44, 2) Then 2 is used

If BitAND(44, 4) Then 4 is used

If BitAND(44, 8) Then 8 is used

If BitAND(44, 16) Then 16 is used

If BitAND(44, 32) Then 32 is used


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eMyvnE

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JohnOne,

You are correct - it is binary. Are you sitting comfortably? Then let us begin....

First AND and OR. An AND operation is only true if BOTH elemnts have the bit set. An OR operation is true if EITHER of the elements have the bit set:

0010
AND
    0111 will give 0010 because only that bit is set in BOTH

    0010
OR
    0111 will give 0111 because those bits are set in EITHER one of the elements

Ther is also XOR, which is true only if the bits are different in each element :P - but we will not go there today!

Look at those flags you mentioned in binary (remember we go up in powers of 2:

Power of 2   7   6   5   4   3   2   1   0

Value        128 64  32  16  8   4   2   1

1                                        x  = binary 00000001
2                                    x      = binary 00000010
4                                x          = binary 00000100
...
64               x                          = binary 01000000

And

44                   x       x   x          = 32 + 8 + 4 = binary 00101100

So in essence you have to check whether a particulr bit is set in the number - gets complicated!

But AutoIt uses the Bit* functions to help you use the decimal numbers that we (or at least some of us) are more used to dealing with. So to see if the flags 32, 8 and 4 are set we use BitAND:

$iMask = 44 ; 00101100

For $i = 43 To 45
    If BitAnd($i, $iTest) = $iMask Then ConsoleWrite($i & " matches!" & @CRLF)
Next

Note that we match both 44 and 45 as the flags are set in both cases:

43 = 00101011 = __X_X_xx = not all our flags set
44 = 00101100 = __X_XX__ = all our flags set
45 = 00101101 = __X_XX_x = all our flags set - even though there are others also set!

Remember we are looking at individual bits and not the whole number. If we wanted to do that we could just use If $i = $iMask. :mellow:

We use BitOR to add styles for a similar reason. It makes sure that only the bits associated with that particular style are set. If we added the actual values of the styles together we could end up with a number which set the wrong bits:

Style 1 = 17 = 00010001
Style 3 = 33 = 00100001

If we add we get 50: 00110010 and the flag bit are wrongly set
If we BitOR we get:  00110001 and the flag bits are correctly set

See the difference? Most of the time there is not a problem - but it best to use BitOr to be sure.

Is that enough to be going on with? :party:

M23


Any of my own code posted anywhere on the forum is available for use by others without any restriction of any kind._______My UDFs:

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#5 ·  Posted (edited)

I found Siao's "Bitwise operations visualiser" gave me ein wenig Verstehen, (a little understanding) of bitwise operations.

Also see post #8 of that thread.

Edited by Malkey

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#6 ·  Posted (edited)

I wrote also a converter where you can enter binary or integer value which will be converted appropriately to the other format.

Integer <=> Binary Converter

BR,

UEZ

Edited by UEZ

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Don't forget you have a nice calculator doing most usual conversion for you: the Windows calculator. Just don't forget to switch to Scientific display to have access to numeric conversions between any two of decimal, hexadecimal, octal and binary for 8-, 16-, 32- or 64-bit wide values.


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PCRE v8.33 regexp documentation latest available release and currently implemented in AutoIt beta.

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SQL tutorial (covers "generic" SQL, but most of it applies to SQLite as well)
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SQLite official website with full documentation (may be newer than the SQLite library that comes standard with AutoIt)

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