Question

How to check if all bits of a number are set in PHP

Answer 1

function print_bits($n) {
    for ($i = 3; $i >= 0; $i--) {
        echo ($n >> $i) & 1;
    }
    echo "<br />";
}

function is_all_bits_set($n) {
   return ($n + 1) & $n;
}

$n = 15;

print_bits($n);
print_bits($n + 1);
print_bits(($n + 1) & $n);
if (is_all_bits_set($n) == 0) {
    echo "Yes" . "<br />";
} else {
    echo "No" . "<br />";
}

$n = 13;

print_bits($n);
print_bits($n + 1);
print_bits(($n + 1) & $n);
if (is_all_bits_set($n) == 0) {
    echo "Yes" . "<br />";
} else {
    echo "No" . "<br />";
}
 


/*
run:
      
1111
0000
0000
Yes
1101
1110
1100
No
     
*/

 

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Answer 2

function print_bits($n) {
    for ($i = 3; $i >= 0; $i--) {
        echo ($n >> $i) & 1;
    }
    echo "<br />";
}

function is_all_bits_set($n) {
    while ($n > 0) {
        if (($n & 1) == 0) {
            return 0;
        }
        $n = $n >> 1;
    }
    return 1;
}

$n = 15;

print_bits($n);
if (is_all_bits_set($n)) {
    echo "Yes" . "<br />";
} else {
    echo "No" . "<br />";
}

$n = 13;

print_bits($n);
if (is_all_bits_set($n)) {
    echo "Yes" . "<br />";
} else {
    echo "No" . "<br />";
}
 
 
/*
run:
      
1111
Yes
1101
No
     
*/

 

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