decbin

(PHP 4, PHP 5, PHP 7, PHP 8)

decbin — Wandelt von dezimal zu binär um

Beschreibung ¶

decbin(int $num): string

Gibt die binäre Darstellung der in num angegebenen Ganzzahl als Zeichenkette zurück.

Parameter-Liste ¶

num

Der umzuwandelnde Dezimalwert.

**Wertebereich der Eingabe unter 32bit-Systemen**
positive `num`	negative `num`	Rückgabewert
0		0
1		1
2		10
... weiterer Verlauf ...
2147483646		1111111111111111111111111111110
2147483647 (größte vorzeichenbehaftete Ganzzahl)		1111111111111111111111111111111 (31 Einsen)
2147483648	-2147483648	10000000000000000000000000000000
... weiterer Verlauf ...
4294967294	-2	11111111111111111111111111111110
4294967295 (größte vorzeichenlose Ganzzahl)	-1	11111111111111111111111111111111 (32 Einsen)

**Wertebereich der Eingabe unter 64bit-Systemen**
positive `num`	negative `num`	Rückgabewert
0		0
1		1
2		10
... weiterer Verlauf ...
9223372036854775806		111111111111111111111111111111111111111111111111111111111111110
9223372036854775807 (größte vorzeichenbehaftete Ganzzahl)		111111111111111111111111111111111111111111111111111111111111111 (63 Einsen)
	-9223372036854775808	1000000000000000000000000000000000000000000000000000000000000000
... weiterer Verlauf ...
	-2	1111111111111111111111111111111111111111111111111111111111111110
	-1	1111111111111111111111111111111111111111111111111111111111111111 (64 Einsen)

Rückgabewerte ¶

Binärdarstellung von num als Zeichenkette.

Beispiele ¶

Beispiel #1 decbin()-Beispiel

<?php
echo decbin(12) . "\n";
echo decbin(26);
?>

Das oben gezeigte Beispiel erzeugt folgende Ausgabe:

1100
11010

Siehe auch ¶

bindec() - Wandelt von binär zu dezimal um
decoct() - Wandelt von dezimal zu oktal um
dechex() - Wandelt von dezimal zu hexadezimal um
base_convert() - Wandelt einen numerischen Wert zwischen verschiedenen Zahlensystemen um
printf() - Liefert einen formatierten String unter Verwendung von %b, %032b oder %064b als Format
sprintf() - Gibt einen formatierten String zurück unter Verwendung von %b, %032b oder %064b als Format

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User Contributed Notes 9 notes

down

MarcelG ¶

11 years ago

To add leading zeros I prefer the following:
<?php
// Add leading zeros
$bin = sprintf( "%08d", decbin( 26 )); // "00011010"
?>

down

rambabusaravanan at gmail dot com ¶

8 years ago

Print as binary format with leading zeros into a variable in one simple statement.

<?php
    $binary = sprintf('%08b',  $decimal);    // $decimal = 5;
    echo $binary;    // $binary = "00000101";
?>

down

Xavier Daull ¶

19 years ago

A fast function to convert a binary string to a bit sequence

<?php

function BinString2BitSequence($mystring) {    
    $mybitseq = "";
    $end = strlen($mystring);
    for($i = 0 ; $i < $end; $i++){
        $mybyte = decbin(ord($mystring[$i])); // convert char to bit string
        $mybitseq .= substr("00000000",0,8 - strlen($mybyte)) . $mybyte; // 8 bit packed
    }
    return $mybitseq;
}

echo BinString2BitSequence("ABCDEF"); // OUTPUT=010000010100001001000011010001000100010101000110

?>

down

coverup ¶

8 years ago

Regarding trailing zeros, after test all the option mention here by others, i have performed my own tests regarding efficiency, here are the results:

<?php

$decimal = 9;

$time_start = microtime(true);
for ($i=0;$i<1000;$i++){
$bin = printf('%08b',  $decimal);
}
$time_end = microtime(true);
$time = $time_end - $time_start;
echo "<hr>Duracion $time segundos<br>\n";
echo $bin . '<br>';

$time_start = microtime(true);
for ($i=0;$i<1000;$i++){
$bin = sprintf( "%08d", decbin( $decimal ));
}
$time_end = microtime(true);
$time = $time_end - $time_start;
echo "<hr>Duracion $time segundos<br>\n";
echo $bin . '<br>';

$time_start = microtime(true);
for ($i=0;$i<1000;$i++){
$bin = decbin($decimal);
$bin = substr("00000000",0,8 - strlen($bin)) . $bin;
}
$time_end = microtime(true);
$time = $time_end - $time_start;
echo "<hr>Duracion $time segundos<br>\n";
echo $bin . '<br>';

?>

results

0000100100001001000010010000100.... (output is echoed 1000 times)
Duracion 0.0134768486023 segundos
8
Duracion 0.00054407119751 segundos
00001001
Duracion 0.000833988189697 segundos
00001001

Thus the winner is 
<?php
$bin = sprintf( "%08d", decbin( $decimal ));
?>

down

noname at example dot com ¶

9 years ago

If you want leading zeros use php built-in features instead of custom functions

<?php
printf('%08b',  $decimal);
?>

>> printf('%08b', E_NOTICE)
>> 00001000

down

Anonymous ¶

19 years ago

Just an example:
If you convert 26 to bin you'll get 11010, which is 5 chars long. If you need the full 8-bit value use this:

$bin = decbin(26);
$bin = substr("00000000",0,8 - strlen($bin)) . $bin;

This will convert 11010 to 00011010.

down

dj.luiting(.a.t.)gmail.com ¶

11 years ago

hi folks, i struggled for a day to get a big decimal number converted into binary, on the windows platform.
finally with bcmath functions this is what worked for me.

function bc_convert2bin($string) {

    //got it to work with bcmath functions, works for 64 bit on 32 bit windows machine
    $finished=0;
    $base=2;
    $bin_nr='';

    if(preg_match("/[^0-9]/", $string)) {
        for($i=0; $string!=chr($i); $i++) {
            $dec_nr=$i;
        }
    } else {
        $dec_nr=$string;
    }
    //while( $dec_nr>$base ) {
    while( bccomp($dec_nr,$base) == 1 ) {

        //$base=$base*2;
        $base=bcmul($base,'2');
        //if($base>$dec_nr) {
        if( bccomp($base,$dec_nr) == 1 ) {
            //$base=$base/2;
            $base=bcdiv($base,'2');
            break;
        }
    }

    while(!$finished) {

        //if(($dec_nr-$base)>0) {
        if( bccomp( bcsub($dec_nr,$base) , 0) == 1 ) {

            //$dec_nr=$dec_nr-$base;
            $dec_nr=bcsub($dec_nr,$base);
            $bin_nr.=1;
            //$base=$base/2;
            $base=bcdiv($base,'2');

        //} elseif(($dec_nr-$base)<0) {
        } elseif( bccomp( bcsub($dec_nr,$base) , 0) == -1 ) {

            $bin_nr.=0;
            //$base=$base/2;
            $base=bcdiv($base,'2');

        //} elseif(($dec_nr-$base)==0) {
        } elseif( bccomp( bcsub($dec_nr,$base) , 0) == 0 ) {

            $bin_nr.=1;
            $finished=1;
            //while($base>1) {
            while( bccomp($base,1) == 1 ) {

                $bin_nr.=0;
                //$base=$base/2;
                $base=bcdiv($base,'2');

            }
        }
    }
    return $bin_nr;
}

down

php at silisoftware dot com ¶

23 years ago

Another larger-than-31-bit function.
Works for very large numbers, but at the expense of perfect bit-precision as the size increases (I noticed rounding errors past 16 or so decimal places) so use with caution, and only when decbin() won't cut it.

function Dec2Bin($number) {
    while ($number >= 256) {
        $bytes[] = (($number / 256) - (floor($number / 256))) * 256;
        $number = floor($number / 256);
    }
    $bytes[] = $number;
    for ($i=0;$i<count($bytes);$i++) {
        $binstring = (($i == count($bytes) - 1) ? decbin($bytes[$i]) : str_pad(decbin($bytes[$i]), 8, "0", STR_PAD_LEFT)).$binstring;
    }
    return $binstring;
}

down

malcolm.murphy ¶

8 years ago

The GNU MP library (http://php.net/manual/en/book.gmp.php) provides methods to efficiently convert binary strings of any length to their binary representation (i.e., a `decbin` equivalent for strings).

<?php

$str = random_bytes(1024); // binary string example

$result = gmp_strval(gmp_import($str), 2); // see manual for options such as endianness

$zeroPadded = sprintf('%0' . (strlen($str) * 8) . 's', $result); // zero-pad if needed, e.g. with str_pad, or sprintf as shown here

$strAgain = gmp_export(gmp_init($result, 2)); // reverse operation similar to bindec

?>

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