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Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1646

Posted: 07:38am 09 Dec 2022

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Having a senior moment.

Regardless of the current bit state

a=a or 1

Will set the bit but what's the short version of:

if a and 1 then a=a xor 1

Pretty sure that in other dialects it's:

a=a and not 1

Edited 2022-12-09 17:39 by Tinine

Volhout
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Joined: 05/03/2018
Location: Netherlands
Posts: 5089

Posted: 08:11am 09 Dec 2022

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I understand you are manipulating one bit in integer a.

Your second line (the requested functionality) will check the bit.
If it is zero, nothing happens
When the bit is one it will XOR the variable with that bit (in essence putting it to zero).

The outcome is always this particular bit set to zero.

So the AND with the negated bit is the correct answer.

When a is a boolean, then the shortest solution is:

a=0

PicomiteVGA PETSCII ROBOTS

Tinine
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Location: United Kingdom
Posts: 1646

Posted: 08:22am 09 Dec 2022

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Example: I am expecting a=254

a=255
a=a and not 1 'just want to reset b0
print a

The result is zero

matherp
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Joined: 11/12/2012
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Posts: 10310

Posted: 08:32am 09 Dec 2022

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a=a and INV 1

IanRogers

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Joined: 09/12/2022
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Posts: 151

Posted: 08:34am 09 Dec 2022

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If you and with 254 you will preserve the rest of 'a' but reset b0

a = a and 254

I'd give my left arm to be ambidextrous

Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1646

Posted: 08:43am 09 Dec 2022

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That's QB64

@matherp: That works! Cheers

Not in my DOS version though but it's not the latest.

Craig

matherp
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Posted: 08:47am 09 Dec 2022

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I implemented INV in the CMM2 and have added it to most of my ports. It is the exact equivalent of the C ~ operator which is the standard way of clearing bits

To set bit n assuming numbering from 0

a |= (1<<n)

to clear bit n

a &= ~(1<<n)

Tinine
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Joined: 30/03/2016
Location: United Kingdom
Posts: 1646

Posted: 08:58am 09 Dec 2022

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IanRogers said If you and with 254 you will preserve the rest of 'a' but reset b0

a = a and 254

Sure, but what I like to do is:

const actuator_1 = &h01
const actuator_2 = &h02

outputs = outputs or actuator_1
outputs = outputs and inv actuator_2

Then I update the DOUTs using the PORT command.

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