bit wise counter on a single byte javascript

Question

I want to use the bits valued at 2^4-2^8 in a Typed 16Uint array item to use as a binary counter to 16.

0000111100000000 ->15
0000111000000000 ->14
0000110100000000 ->13
...
0000000000000000 ->0

is there a simple bit wise operation that would count in binary? my current strategy is to extract the bits as number add one - do some error checking, then set the bits in the original with a&0 and replace that part with a |or mask?

cellBinary = iterate(cellBinary, 16, 4);
function iterate(cellBinary, start, length)
    {
    let number = extractBits(cellBinary, start, length);
    if(number < 15)
        {
        number++;
    }
    what = eraseIterator(what);
    what = what|number;
    return what;
}
function extractBits(what, start, length)
    {
    return ((1 << start ) -1) & (what >> (length - 1));
}
function eraseIterator(what)
    {
    what&16^1; //also iffy if this will work as intended.
    what&32^1; //this is supposed to set 16-128 to 0.
    what&64^1;
    what&128^1; 
    return what;
}

is there a better way to accomplish this? note: code is an example, I'm looking for a strategy, not a bug.

user555045 · Accepted Answer · 2020-03-26 06:58:12Z

1

You could add the right amount directly: 256, 100000000 in binary.

For example,

000000000000 + 100000000 ->
000100000000
001000000000
001100000000
...
111100000000

the bits valued at 2^4-2^8

That would mean this sequence:

Or in other words, add 16.

answered Mar 26, 2020 at 6:58

user555045

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3 Comments

user555045 Over a year ago

@altruios much easier: if (value < 0xF0) value += 16

user555045 Over a year ago

Or 0xF00 and 256 for the version with 8 padding bits, it's not really clear to me which one of them you meant

altruios Over a year ago

so: that makes a lot of sense. i'm not used to working with bitwise stuff, that seems like a really good way to think about it.

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