Math 函数
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PHP手册

bindec

(PHP 4, PHP 5)

bindec — 二进制转换为十进制

说明

number bindec ( string $binary_string )

返回 binary_string 参数所表示的二进制数的十进制等价值。

bindec() 将一个二进制数转换成 integer。可转换的最大的数为 31 位 1 或者说十进制的 2147483647。PHP 4.1.0 开始，该函数可以处理大数值，这种情况下，它会返回 float 类型。

Example #1 bindec() 范例

<?php
echo bindec('110011') . "\n";
echo bindec('000110011') . "\n";
 
echo bindec('111');
?>

以上例程会输出：

51
51
7

参见 decbin()，octdec()，hexdec() 和 base_convert()。

参数

binary_string

The binary string to convert

Warning

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

返回值

The decimal value of binary_string

更新日志

版本 说明
Since 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.

范例

Example #2 bindec() example

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

echo bindec('111');
?>

以上例程会输出：

51
51
7

Example #3 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";
}
?>

以上例程在 32 位机器上的输出:

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

以上例程在 64 位机器上的输出:

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

参见

Math 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 二进制转换为十进制

用户评论:

info at rickdg dot nl (01-Apr-2010 12:40)

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;
    }
} ?>

Nitrogen (21-Jul-2009 03:27)

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.

nodarinodo at mail dot ru (08-Jan-2009 07:51)

<?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;
    }
?>

flashpack at gmail dot com (16-Nov-2008 12:40)

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 ;
}
?>

mashematician at gmail dot com (13-Mar-2008 04:57)

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');

?>

alan hogan dot com slash contact (09-Nov-2007 09:34)

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);
}
?>

gwbdome at freenet dot de (19-Aug-2004 10:43)

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));
 }

martin at punix dot de (30-May-2003 06:47)

## 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)

php at silisoftware dot com (01-Mar-2002 03:16)

For converting larger-than-31-bit numbers:

<?php
function Bin2Dec($binstring) {
    for ($i=0;$i<strlen($binstring);$i++) {
        $decvalue += ((int) substr($binstring, strlen($binstring) - $i - 1, 1)) * pow(2, $i);
    }
    return $decvalue;
}
?>