CODEWITHSUNDEEP
phpintbit
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spreadzz

Reputation: 278

Convert int into bits representation in php

How can you convert a integer into it's bits representation?

For example number 9 representation in bits is: 10011

For example to convert a bit sequence into it's int representation you can do this:

$bits_sq = array(1,0,0,1,1);

function convert_bits_to_int($bits_sq){
    $sum = 0;
    for($i=0; $i < count($bits_sq); $i++){
       $sum = $sum + $bits_sq[$i] * pow(-2, $i);
    }
    print $sum; // equals to 9
}

But I want the other way around.

Edit: DO NOT MISTAKE BITS WITH BINARY, THIS IS NOT THE DUPLICATE NEITHER HAS THE ANSWER IN THE ABOVE THREAD

Upvotes: -3

Views: 5948

Answers (4)

Tim Dearborn
Tim Dearborn

Reputation: 1177

Below is a function I wrote to convert a decimal to an array of bits, with the lowest bit having an index of 1.

/*
Function to convert positive decimal to array of bits with the lowest bit having an index of 1.
@param int $int - Positive decimal to covert (Not sure if negative numbers will give correct result)
@param int $min_bits (Optional) - Minimum number of elements in array
@return array - Array of bits with the lowest indexed as 1
Example: decbits(5, 8) returns array(1=>1, 2=>0, 3=>1, 4=>0, 5=>0, 6=>0, 7=>0, 8=>0)
*/

function decbits($int, $min_bits=1) {
    // Convert int into binary
    $int = intval($int);
    $min_bits = intval($min_bits);
    $bin = decbin($int);
    $binstr = strval($bin);

    // Reverse string and populate array
    $binstr = strrev($binstr);  
    $bit_array = str_split($binstr);

    // Ensure array has minimum number of elements
    $bit_array = array_pad($bit_array, $min_bits, 0);
    
    //  Reindex array, starting at 1
    array_unshift($bit_array,'0');
    unset($bit_array[0]);

    return $bit_array;
}

Upvotes: 0

Philip Borbon
Philip Borbon

Reputation: 712

Just dropping this here.

echo str_pad(decbin(1), 4, '0', STR_PAD_LEFT); // 0001
echo str_pad(decbin(7), 4, '0', STR_PAD_LEFT); // 0111
echo str_pad(decbin(9), 4, '0', STR_PAD_LEFT); // 1001

Upvotes: 0

Richard Chambers
Richard Chambers

Reputation: 17623

My php is rusty however if you want to do the reverse of this example

$bits_sq = array(1,0,0,1,1);

function convert_bits_to_int($bits_sq){
    $sum = 0;
    for($i=0; $i < count($bits_sq); $i++){
       $sum = $sum + $bits_sq[$i] * pow(-2, $i);
    }
    print $sum; // equals to 9
}

then I suppose you want something like:

$bits_sq = convert_int_to_bits ($iValue);
function convert_int_to_bits ($iValue) {
  $bits = array();  // initialize the array
  do {
    $bits[] = ($iValue & 1);
    $iValue >>= 1;    // shift the bit off so that we go to the next one
  } while ($iValue);  // continue as long as there are still some bits.
  // we have the bits in reverse order so lets reverse it.
  return array_reverse($bits);
}

Upvotes: 3

Jack
Jack

Reputation: 3415

You need to use decbin() to convert an integer to binary.

http://php.net/manual/en/function.decbin.php

enter image description here

Upvotes: 5

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