bindec

(PHP 4, PHP 5)

bindecBinary to decimal

Description

number bindec ( string $binary_string )

Returns the decimal equivalent of the binary number represented by the binary_string argument.

bindec() converts a binary number to an integer or, if needed for size reasons, float.

bindec() interprets all binary_string values as unsigned integers. This is because bindec() sees the most significant bit as another order of magnitude rather than as the sign bit.

Parameters

binary_string

The binary string to convert

Warning

The parameter must be a string. Using other data types will produce unexpected results.

Return Values

The decimal value of binary_string

Changelog

Version Description
4.1.0 The function can now convert numbers that are too large to fit into the platforms integer type, larger values are returned as float in that case.

Examples

Example #1 bindec() example

<?php
echo bindec('110011') . "\n";
echo 
bindec('000110011') . "\n";

echo 
bindec('111');
?>

The above example will output:

51
51
7

Example #2 bindec() interprets input as unsigned integers

<?php
/*
 * The lesson from this example is in the output
 * rather than the PHP code itself.
 */

$magnitude_lower pow(2, (PHP_INT_SIZE 8) - 2);
p($magnitude_lower 1);
p($magnitude_lower'See the rollover?  Watch it next time around...');

p(PHP_INT_MAX'PHP_INT_MAX');
p(~PHP_INT_MAX'interpreted to be one more than PHP_INT_MAX');

if (
PHP_INT_SIZE == 4) {
    
$note 'interpreted to be the largest unsigned integer';
} else {
    
$note 'interpreted to be the largest unsigned integer
              (18446744073709551615) but skewed by float precision'
;
}
p(-1$note);


function 
p($input$note '') {
    echo 
"input:        $input\n";

    
$format '%0' . (PHP_INT_SIZE 8) . 'b';
    
$bin sprintf($format$input);
    echo 
"binary:       $bin\n";

    
ini_set('precision'20);  // For readability on 64 bit boxes.
    
$dec bindec($bin);
    echo 
'bindec():     ' $dec "\n";

    if (
$note) {
        echo 
"NOTE:         $note\n";
    }

    echo 
"\n";
}
?>

Output of the above example on 32 bit machines:

input:        1073741823
binary:       00111111111111111111111111111111
bindec():     1073741823

input:        1073741824
binary:       01000000000000000000000000000000
bindec():     1073741824
NOTE:         See the rollover?  Watch it next time around...

input:        2147483647
binary:       01111111111111111111111111111111
bindec():     2147483647
NOTE:         PHP_INT_MAX

input:        -2147483648
binary:       10000000000000000000000000000000
bindec():     2147483648
NOTE:         interpreted to be one more than PHP_INT_MAX

input:        -1
binary:       11111111111111111111111111111111
bindec():     4294967295
NOTE:         interpreted to be the largest unsigned integer

Output of the above example on 64 bit machines:

input:        4611686018427387903
binary:       0011111111111111111111111111111111111111111111111111111111111111
bindec():     4611686018427387903

input:        4611686018427387904
binary:       0100000000000000000000000000000000000000000000000000000000000000
bindec():     4611686018427387904
NOTE:         See the rollover?  Watch it next time around...

input:        9223372036854775807
binary:       0111111111111111111111111111111111111111111111111111111111111111
bindec():     9223372036854775807
NOTE:         PHP_INT_MAX

input:        -9223372036854775808
binary:       1000000000000000000000000000000000000000000000000000000000000000
bindec():     9223372036854775808
NOTE:         interpreted to be one more than PHP_INT_MAX

input:        -1
binary:       1111111111111111111111111111111111111111111111111111111111111111
bindec():     18446744073709551616
NOTE:         interpreted to be the largest unsigned integer
              (18446744073709551615) but skewed by float precision

See Also

add a note add a note

User Contributed Notes 9 notes

up
2
alan hogan dot com slash contact
6 years ago
The "smartbindec" function I wrote below will convert any binary string (of a reasonable size) to decimal.  It will use two's complement if the leftmost bit is 1, regardless of bit length.  If you are getting unexpected negative answers, try zero-padding your strings with sprintf("%032s", $yourBitString).

<?php
function twoscomp($bin) {
   
$out = "";
   
$mode = "init";
    for(
$x = strlen($bin)-1; $x >= 0; $x--) {
        if (
$mode != "init")
           
$out = ($bin[$x] == "0" ? "1" : "0").$out;
        else {
            if(
$bin[$x] == "1") {
               
$out = "1".$out;
               
$mode = "invert";
            }
            else
               
$out = "0".$out;
        }
    }
    return
$out;
}
function
smartbindec($bin) {
    if(
$bin[0] == 1)
        return -
1 * bindec(twoscomp($bin));
    else return (int)
bindec($bin);
}
?>
up
1
Nitrogen
5 years ago
Binary to Decimal conversion using the BCMath extension..

<?php

function BCBin2Dec($Input='') {
 
$Output='0';
  if(
preg_match("/^[01]+$/",$Input)) {
    for(
$i=0;$i<strlen($Input);$i++)
     
$Output=BCAdd(BCMul($Output,'2'),$Input{$i});
  }
  return(
$Output);
}

?>

This will simply convert from Base-2 to Base-10 using BCMath (arbitrary precision calculation).

See also: my 'BCDec2Bin' function on the 'decbin' document.
Enjoy,
Nitrogen.
up
2
gwbdome at freenet dot de
10 years ago
i think a better method than the "shift-method" is my method ^^...
here it comes:

function convert2bin($string) {
     $finished=0;
     $base=1;
     if(preg_match("/[^0-9]/", $string)) {
         for($i=0; $string!=chr($i); $i++);
         $dec_nr=$i;
     }
     else $dec_nr=$string;
     while($dec_nr>$base) {
         $base=$base*2;
         if($base>$dec_nr) {
             $base=$base/2;
             break;
         }
     }
     while(!$finished) {
         if(($dec_nr-$base)>0) {
             $dec_nr=$dec_nr-$base;
             $bin_nr.=1;
             $base=$base/2;
         }
         elseif(($dec_nr-$base)<0) {
             $bin_nr.=0;
             $base=$base/2;
         }
         elseif(($dec_nr-$base)==0) {
             $bin_nr.=1;
             $finished=1;
             while($base>1) {   
                 $bin_nr.=0;
                 $base=$base/2;
             }
         }
     }
     return $bin_nr;
}

=====================================================

if you want to reconvert it (from binary to string or integer) you can use this function:

function reconvert($bin_nr) {
     $base=1;
     $dec_nr=0;
     $bin_nr=explode(",", preg_replace("/(.*),/", "$1", str_replace("1", "1,", str_replace("0", "0,", $bin_nr))));
     for($i=1; $i<count($bin_nr); $i++) $base=$base*2;
     foreach($bin_nr as $key=>$bin_nr_bit) {
         if($bin_nr_bit==1) {
             $dec_nr+=$base;
             $base=$base/2;
         }
         if($bin_nr_bit==0) $base=$base/2;
     }
     return(array("string"=>chr($dec_nr), "int"=>$dec_nr));
}
up
2
martin at punix dot de
11 years ago
## calculate binary with "shift-method" ##

<?php
function dec2bin($decimal_code){
for(
$half=($decimal_code);$half>=1;$half=(floor($half))/2){
   if((
$half%2)!=0){
   
$y.=1;
   }
   else{
   
$y.=0;
   }
  }
$calculated_bin=strrev($y);
return
$calculated_bin;
}
?>

## example ##

[bin] 123 = [dec] 1111011

e.g.
123/2 = 61,5 => 1
61/2  = 30,5 => 1
30/2  = 15   => 0
15/2  = 7,5  => 1
7/2   = 3,5  => 1
3/2   = 1,5  => 1
1/2   = 0,5  => 1
(0/2   = 0    finish)
up
1
info at rickdg dot nl
4 years ago
Two functions to convert 16bit or 8bit binary to integer using two's complement. If input exceeds maximum bits, false is returned. Function is easily scalable to x bits by changing the hexadecimals.

<?php function _bin16dec($bin) {
   
// Function to convert 16bit binary numbers to integers using two's complement
   
$num = bindec($bin);
    if(
$num > 0xFFFF) { return false; }
    if(
$num >= 0x8000) {
        return -((
$num ^ 0xFFFF)+1);
    } else {
        return
$num;
    }
}

function
_bin8dec($bin) {
   
// Function to convert 8bit binary numbers to integers using two's complement
   
$num = bindec($bin);
    if(
$num > 0xFF) { return false; }
    if(
$num >= 0x80) {
        return -((
$num ^ 0xFF)+1);
    } else {
        return
$num;
    }
}
?>
up
1
nodarinodo at mail dot ru
5 years ago
<?php   
// bindecfunc :)))) I think it works well too :)
function bindecc($str)
    {
       
$str = str_replace(" ", "", $str);
       
$strr = preg_match('/[^01]/', $str);
        if(
$strr == 1) { return "<b> Error ! only 1 and 0;</b>"; }
       
$strsig = strlen($str);
       
$strr1 = strrev($str);
       
$strf = '';
        for(
$i = $strsig; $i >= 0; $i--)
        {
           
$strf += ($strr1[$i] * pow(2, $i));
           
#$strf += $str[$i];
       
}
        return
$strf;
    }
?>
up
0
patrick dot boens at latosensu dot be
2 years ago
Left-shift a string by a number of bytes
<?php
function STR_shl( $szStr,$nBits )
/*-----------------------------*/
{
    if (
$nBits < 1 || $nBits > 7 )                                     /* If not adequate number of bits */
   
{
        return (
$szStr );                                              /* Return the original string */
   
}   /* if ( $nBits < 1 || $nBits > 7 ) */

   
if ( ( $iLength = strlen( $szStr ) ) <= 0 )                         /* If string empty */
   
{
        return (
$szStr );                                              /* Return the original string */
   
}   /* if ( ( $iLength = strlen( $szStr ) ) <= 0 ) */

   
$szRetVal   = '';                                                   /* Create an empty string */

   
$szBits     = STR_Binary( $szStr );                                 /* $szStr in bits */
   
$szLostBits = STR_Left( $szBits,$nBits );                           /* The $nBits leftmost bits of the string */
   
$szShifted  = substr( $szBits,$nBits ) . $szLostBits;               /* $szStr left shifted */

   
for ( $i = 0;$i < $iLength;$i++ )                                   /* Treat the entire string (per slice of 8 bits) */
   
{
       
$szRetVal .= chr( bindec( substr( $szShifted,$i * 8,8 ) ) );    /* Concatenate the CHR to the result string */
   
}   /* for ( $i = 0;$i < $iLength;$i++ ) */

   
return ( $szRetVal );                                               /* Return result to caller */
}
?>

Right-shift a string by a number of bytes
<?php

function STR_shr( $szStr,$nBits )
/*-----------------------------*/
{
    if (
$nBits < 1 || $nBits > 7 )                                     /* If not adequate number of bits */
   
{
        return (
$szStr );                                              /* Return the original string */
   
}   /* if ( $nBits < 1 || $nBits > 7 ) */

   
if ( ( $iLength = strlen( $szStr ) ) <= 0 )                         /* If string empty */
   
{
        return (
$szStr );                                              /* Return the original string */
   
}   /* if ( ( $iLength = strlen( $szStr ) ) <= 0 ) */

   
$szRetVal   = '';                                                   /* Create an empty string */

   
$szBits     = STR_Binary( $szStr );                                 /* $szStr in bits */
   
$szLostBits = STR_Right( $szBits,$nBits );                          /* The $nBits rightmost bits of the string */
   
$szShifted  = $szLostBits . substr( $szBits,0,-$nBits );            /* $szStr right shifted */

   
for ( $i = 0;$i < $iLength;$i++ )                                   /* Treat the entire string (per slice of 8 bits) */
   
{
       
$szRetVal .= chr( bindec( substr( $szShifted,$i * 8,8 ) ) );    /* Concatenate the CHR to the result string */
   
}   /* for ( $i = 0;$i < $iLength;$i++ ) */

   
return ( $szRetVal );                                               /* Return result to caller */
}
?>

Additional functions used by the two preceding:
<?php
function STR_Binary( $szStr )
/*-------------------------*/
{
   
$szRetVal = '';                                                     /* Ready to return an empty string */

   
if ( ( $iLength = strlen( $szStr ) ) > 0 )                          /* If string NOT empty */
   
{
        for (
$i = 0; $i < $iLength;$i++ )                              /* Treat each character of the string */
       
{
           
$szRetVal .= sprintf( '%08b',ord( $szStr[$i] ) );           /* Turn this char to a binary representation (8 bits) */
       
}   /* for ( $i = 0; $i < $iLength;$i++ ) */
   
}   /* if ( ( $iLength = strlen( $szStr ) ) > 0 ) */

   
return ( $szRetVal );                                               /* Return result to caller */
}

function
STR_Left( $szStr,$iCount = 1 )
/*----------------------------------*/
{
    return
substr( $szStr,0,$iCount );
}  
/* End of function strleft() */

function STR_Right( $szString,$iCount )
/*----------------------------------*/
{
    return
substr( $szString,0 + strlen( $szString ) - $iCount,$iCount );
}
?>
up
0
flashpack at gmail dot com
5 years ago
for converting fractions :
eg : 1001.1101

<?php
function BinaryToDecimal($binary){
 
$binary=trim($binary);
  if (
strstr($binary,'.')){
   
$split=explode('.',$binary);
   
$integer=$split[0];
   
$fraction=$split[1];

   
$digits=str_split($fraction);
   
$num=sizeof($digits);
    for (
$i=1; $i<=$num;$i++){
      if (
$digits[$i-1]>1){
        echo
'<script>alert("Enter Binary Digits Only {0,1}\n \n eg: 11001 or 11001.011");history.go(-1)</script> ';
      }
     
$exponent=pow(2,-$i);
     
$fraction_result+=$digits[$i-1]*$exponent;
    }

  }else{
   
$integer=$binary;
  }

 
$splits=str_split($integer);
 
$num=sizeof($splits)-1;
 
$i=$num;
  foreach(
$splits as $digits){
    if (
$digits>1){
      echo
'<script>alert("Enter Binary Digits Only {0,1}\n \n eg: 11001 or 11001.011");history.go(-1)</script> ';
    }
   
$exponent=pow(2,$i);
   
$integer_result+=$digits*$exponent;
   
$i--;
  }
  if(
$fraction_result){
   
$result=$integer_result+$fraction_result;
  }else {
   
$result=$integer_result;
  }
  return
$result ;
}
?>
up
-1
mashematician at gmail dot com
6 years ago
A binary to decimal conversion function that takes advantage of the BC library functions to return decimal values of arbitrary length.

Input type must be a string in order to work properly.

<?php

function binary_to_decimal($a) {
   
$bin_array = str_split($a);

   
$y=sizeof($bin_array)-1;
    for (
$x=0; $x<sizeof($bin_array)-1; $x++) {
        if (
$bin_array[$x] == 1) {
           
$bin_array[$x] = bcpow(2, $y);
        }
       
$y--;
    }
   
    for (
$z=0; $z<sizeof($bin_array); $z++) {
       
$result = bcadd($result, $bin_array[$z]);
    }
    echo
$result;
}

binary_to_decimal('11111');

?>
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