base_convert

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

base_convert — 数値の基数を任意に変換する

説明

base_convert(string $num, int $from_base, int $to_base): string

num を基数 to_base で表した文字列を返します。 num の基数は、 from_base で指定します。 from_base および to_base は、ともに 2 から 36 までである必要があります。 10 より大きな基数を有する数の各桁は、文字 a-z で表されます。この場合、a は 10、b は 11、z は 35 を意味します。 num は、大文字小文字を区別せずに扱います。

警告

大きな数値で base_convert() を使用すると、精度が失われてしまうことがあります。これは、内部で使用している float の性質によるものです。詳細な情報や制限についてはマニュアルの浮動小数点数のセクションを参照ください。

パラメータ

num: 変換する数値。 num に無効な文字が含まれている場合は、何もエラーを出さずにただ無視します。 PHP 7.4.0 以降は、無効な文字を与えることは推奨されません。
from_base: 変換前の num の基数。
to_base: 変換後の num の基数。

戻り値

num を基数 to_base で表した値を返します。

変更履歴

バージョン	説明
7.4.0	無効な文字を与えると、非推奨の警告が出るようになりました。結果は不正な文字がなかったかのように計算されます。

例

例1 base_convert() の例

<?php
$hexadecimal = 'a37334';
echo base_convert($hexadecimal, 16, 2);
?>

上の例の出力は以下となります。

101000110111001100110100

参考

intval() - 変数の整数としての値を取得する

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User Contributed Notes 21 notes

down

PHPCoder at niconet2k dot com ¶

13 years ago

Convert an arbitrarily large number from any base to any base.

string convBase(string $numberInput, string $fromBaseInput, string $toBaseInput)
$numberInput number to convert as a string
$fromBaseInput base of the number to convert as a string
$toBaseInput base the number should be converted to as a string
examples for $fromBaseInput and $toBaseInput
'0123456789ABCDEF' for Hexadecimal (Base16)
'0123456789' for Decimal (Base10)
'01234567' for Octal (Base8)
'01' for Binary (Base2) 
You can really put in whatever you want and the first character is the 0.
Examples:

<?php 
convBase('123', '0123456789', '01234567'); 
//Convert '123' from decimal (base10) to octal (base8).
//result: 173

convBase('70B1D707EAC2EDF4C6389F440C7294B51FFF57BB', '0123456789ABCDEF', '01');
//Convert '70B1D707EAC2EDF4C6389F440C7294B51FFF57BB' from hexadecimal (base16) to binary (base2).
//result: 
//111000010110001110101110000011111101010110000101110
//110111110100110001100011100010011111010001000000110
//001110010100101001011010100011111111111110101011110
//111011

convBase('1324523453243154324542341524315432113200203012', '012345', '0123456789ABCDEF');
//Convert '1324523453243154324542341524315432113200203012' from senary (base6) to hexadecimal (base16).
//result: 1F9881BAD10454A8C23A838EF00F50

convBase('355927353784509896715106760','0123456789','Christopher');
//Convert '355927353784509896715106760' from decimal (base10) to undecimal (base11) using "Christopher" as the numbers.
//result: iihtspiphoeCrCeshhorsrrtrh

convBase('1C238Ab97132aAC84B72','0123456789aAbBcCdD', '~!@#$%^&*()');
//Convert'1C238Ab97132aAC84B72' from octodecimal (base18) using '0123456789aAbBcCdD' as the numbers to undecimal (base11) using '~!@#$%^&*()' as the numbers.
//result: !%~!!*&!~^!!&(&!~^@#@@@&

function convBase($numberInput, $fromBaseInput, $toBaseInput)
{
    if ($fromBaseInput==$toBaseInput) return $numberInput;
    $fromBase = str_split($fromBaseInput,1);
    $toBase = str_split($toBaseInput,1);
    $number = str_split($numberInput,1);
    $fromLen=strlen($fromBaseInput);
    $toLen=strlen($toBaseInput);
    $numberLen=strlen($numberInput);
    $retval='';
    if ($toBaseInput == '0123456789')
    {
        $retval=0;
        for ($i = 1;$i <= $numberLen; $i++)
            $retval = bcadd($retval, bcmul(array_search($number[$i-1], $fromBase),bcpow($fromLen,$numberLen-$i)));
        return $retval;
    }
    if ($fromBaseInput != '0123456789')
        $base10=convBase($numberInput, $fromBaseInput, '0123456789');
    else
        $base10 = $numberInput;
    if ($base10<strlen($toBaseInput))
        return $toBase[$base10];
    while($base10 != '0')
    {
        $retval = $toBase[bcmod($base10,$toLen)].$retval;
        $base10 = bcdiv($base10,$toLen,0);
    }
    return $retval;
}
?>

down

ardavies at tiscali dot co dot uk ¶

11 years ago

In order to convert base 26 (hexavigesimal) of just alphanumeric characters (A-Z), wthout integers, (as descibed at http://en.wikipedia.org/wiki/Hexavigesimal), I found this to be useful:

function base_convert_alpha(  $str,  $from,  $to  )
{
    $r = range( 'A', 'Z' );
    $clean = str_replace( $r, array_keys($r), $str );
    return base_convert( $clean, $from, $to );
}

echo base_convert_alpha(  "BAC",  26,  10  );

//$clean = 102 which then returns 678

down

Anonymous ¶

6 years ago

While not immediately clear from the description above, a negative sign is also "silently ignored".

base_convert("-12", 10, 10)   =>   12

down

Clifford dot ct at gmail dot com ¶

12 years ago

If you use base_convert to convert a large (eg. 80-bit) hexadecimal to base-36, you might observe:



ABCDEF00001234567890 (hexadecimal) => 3O47RE02JZSW0KS8 (base-36) => ABCDEF00001240000000 (hexadecimal)



This is normal and is due to the loss of precision on large numbers.



I have written a string-based function using the built-in BC Math Extension which will overcome this and similar problems.



<?php



function str_baseconvert($str, $frombase=10, $tobase=36) {

    $str = trim($str);

    if (intval($frombase) != 10) {

        $len = strlen($str);

        $q = 0;

        for ($i=0; $i<$len; $i++) {

            $r = base_convert($str[$i], $frombase, 10);

            $q = bcadd(bcmul($q, $frombase), $r);

        }

    }

    else $q = $str;

 

    if (intval($tobase) != 10) {

        $s = '';

        while (bccomp($q, '0', 0) > 0) {

            $r = intval(bcmod($q, $tobase));

            $s = base_convert($r, 10, $tobase) . $s;

            $q = bcdiv($q, $tobase, 0);

        }

    }

    else $s = $q;

 

    return $s;

}



?>



Typical use-cases:

1.  Convert a large arbitrary precision number to base-36.

2.  Convert a 32-char hexadecimal UUID (128-bit) to a 25-char base-36 unique key, and vice versa.



Examples:



<?php

$b16 = 'ABCDEF00001234567890';

$b36 = str_baseconvert($b16, 16, 36);

echo ("$b16 (hexadecimal) = $b36 (base-36) \\n");



$uuid = 'ABCDEF01234567890123456789ABCDEF';

$ukey = str_baseconvert($uuid, 16, 36);

echo ("$uuid (hexadecimal) = $ukey (base-36) \\n");

?>



ABCDEF00001234567890 (hexadecimal) = 3o47re02jzqisvio (base-36) 

ABCDEF01234567890123456789ABCDEF (hexadecimal) = a65xa07491kf5zyfpvbo76g33 (base-36)

down

JR ¶

13 years ago

Short arabic2roman conveter:



<?php

function rome($N){

        $c='IVXLCDM';

        for($a=5,$b=$s='';$N;$b++,$a^=7)

                for($o=$N%$a,$N=$N/$a^0;$o--;$s=$c[$o>2?$b+$N-($N&=-2)+$o=1:$b].$s);

        return $s;

}

?>



And it works :)

down

lindsay at bitleap dot com ¶

20 years ago

If you need to use base_convert with numbers larger then 32 bit, the following gmp implementation of base_convert should work.

<?php

/*use gmp library to convert base. gmp will convert numbers > 32bit*/
function gmp_convert($num, $base_a, $base_b)
{
        return gmp_strval ( gmp_init($num, $base_a), $base_b );
}

?>

down

Theriault ¶

15 years ago

If you would like to convert numbers into just the uppercase alphabet base and vice-versa (e.g. the column names in a Microsoft Windows Excel sheet..A-Z, AA-ZZ, AAA-ZZZ, ...), the following functions will do this.

<?php

/**
 * Converts an integer into the alphabet base (A-Z).
 *
 * @param int $n This is the number to convert.
 * @return string The converted number.
 * @author Theriault
 * 
 */
function num2alpha($n) {
    $r = '';
    for ($i = 1; $n >= 0 && $i < 10; $i++) {
        $r = chr(0x41 + ($n % pow(26, $i) / pow(26, $i - 1))) . $r;
        $n -= pow(26, $i);
    }
    return $r;
}
/**
 * Converts an alphabetic string into an integer.
 *
 * @param int $n This is the number to convert.
 * @return string The converted number.
 * @author Theriault
 * 
 */
function alpha2num($a) {
    $r = 0;
    $l = strlen($a);
    for ($i = 0; $i < $l; $i++) {
        $r += pow(26, $i) * (ord($a[$l - $i - 1]) - 0x40);
    }
    return $r - 1;
}

?>

Microsoft Windows Excel stops at IV (255), but this function can handle much larger. However, English words will start to form after a while and some may be offensive, so be careful.

down

AdamJacobMuller at AdamJacobMuller dot com ¶

21 years ago

<?php

function binarycodedstring2dec($binary) {

        $len=strlen($binary);

        $rows=($len/4)-1;

        if (($len%4)>0) {

                $pad=$len+(4-($len%4));

                $binary=str_pad($binary,$pad,"0",STR_PAD_LEFT);

                $len=strlen($binary);

                $rows=($len/4)-1;

        }

        $x=0;

        for ($x=0;$x<=$rows;$x++) {

                $s=($x*4);

                $bins=$binary[$s].$binary[$s+1].$binary[$s+2].$binary[$s+3];

                $num=base_convert($bins,2,10);

                if ($num>9) {

                        die("the string is not a proper binary coded decimal\n");

                } else {

                        $res.=$num;

                }

        }

        return $res;

}

?>



a binary coded decimal is converted by taking groups of four from a decimal string,

for example the binary coded decimal string

1000 = 8

10001000 does not = 136 but 88

so

binarycodedstring2dec(1000) = 8

binarycodedstring2dec(11100000111001)=3839

binarycodedstring2dec(100000111001)=839



i truly have no idea if this function will be useful to anyone, i simply failed a physics midterm because i didn't know this so i wrote this function to make sure i would never forget how to convert binary coded decimals

down

xdv43 at yandex dot ru ¶

2 years ago

Convert Large Integer to Hexadecimal without PHP Math extension.

<?php
/* 
 * Created by Michael Renner  17-May-2006 03:24
*/
function baseConvert($numstring, $frombase, $tobase)
{
 
    $chars = "0123456789abcdefghijklmnopqrstuvwxyz";
    $tostring = substr($chars, 0, $tobase);
 
    $length = strlen($numstring);
    $result = '';
    for ($i = 0; $i < $length; $i++)
    {
        $number[$i] = strpos($chars, $numstring[$i]);
    }
    do
    {
        $divide = 0;
        $newlen = 0;
        for ($i = 0; $i < $length; $i++)
        {
            $divide = $divide * $frombase + $number[$i];
            if ($divide >= $tobase)
            {
                $number[$newlen++] = (int)($divide / $tobase);
                $divide = $divide % $tobase;
            } elseif ($newlen > 0)
            {
                $number[$newlen++] = 0;
            }
        }
        $length = $newlen;
        $result = $tostring[$divide] . $result;
    } while ($newlen != 0);
    return $result;
}

down

ohcc at 163 dot com ¶

7 years ago

<?php
    $v = base_convert(3.14, 10, 10);
    var_dump($v);
?>

output: string(3) "314"

down

tika dot pahadi at selu dot edu ¶

9 years ago

Note that the method can only convert max 1024 long numbers. Most people don't nee that but once I ran into an issue where binary string was converted into alphanumeric. In such case, you need to split them, convert them and join.

down

cyrilbele at yahoo dot fr ¶

16 years ago

If you want to do sharding, at some point you will need to decide which shard to target. Here is a simple function to assign the data to a particular shard based on a key (usually identifier of the row)



Here is a simple function to get the shard based on the key and the number of shards available



<?php

function getShard($key,$nbShards) {

    $num = substr(base_convert(sha1($key), 16, 10),4,6);

    return $num%$nbShards;

}

?>

down

wadelau at gmail dot com ¶

7 years ago

Base62x gives an alternative way for traditional Base62 and/or Base64.

base62x_encode / base62x_decode would be merged into PHP as an extra module in the future.

Prior to that, users can download the PHP extra module via: https://github.com/wadelau/Base62x

down

denik dot od at gmail dot com ¶

11 years ago

Convert any length bits to HEX:

function bits2hex($bin)
{
   $out = "";
   for($i=0;$i<strlen($bin);$i+=8)
   {
      $byte = substr($bin,$i,8); if( strlen($byte)<8 ) $byte .= str_repeat('0',8-strlen($byte));
      $out .= base_convert($byte,2,16);
   }
   return $out;
}

VARNING! If the last byte is incomplete, it is supplemented with zeros as string!

down

Anonymous ¶

7 years ago

some other mini implementation of base32 without error catching. just bring things from 5 to 8 and 8 to 5 bit. greetings. mho

<?
function base32_decode($d)
    {
    list($t, $b, $r) = array("ABCDEFGHIJKLMNOPQRSTUVWXYZ234567", "", "");

    foreach(str_split($d) as $c)
        $b = $b . sprintf("%05b", strpos($t, $c));

    foreach(str_split($b, 8) as $c)
        $r = $r . chr(bindec($c));

    return($r);
    }

function base32_encode($d)
    {
    list($t, $b, $r) = array("ABCDEFGHIJKLMNOPQRSTUVWXYZ234567", "", "");

    foreach(str_split($d) as $c)
        $b = $b . sprintf("%08b", ord($c));

    foreach(str_split($b, 5) as $c)
        $r = $r . $t[bindec($c)];

    return($r);
    }
?>

down

simon at simonster dot com ¶

20 years ago

Here are some functions for converting integers to and from base 256. Converting to base 64 is simple given these.



<?php

function to_base256($number, $from_base = 10) {

    $binary_number = base_convert($number, $from_base, 2);

    $final_string = "";

    $new_length = (ceil(strlen($binary_number)/8)*8);

    $binary_number = str_pad($binary_number, $new_length, "0", STR_PAD_LEFT);

    for($i=($new_length-8); $i>=0; $i-=8) {

        $final_string = chr(base_convert(substr($binary_number, $i, 8), 2, 10)).$final_string;

    }

    return $final_string;

}



function from_base256($string, $to_base = 10) {

    $number = "";

    for($i=0; $i<strlen($string); $i++) {

        $number .= str_pad(base_convert(ord($string{$i}), 10, 2), 8, "0", STR_PAD_LEFT);

    }

    return base_convert($number, 2, $to_base);

}

?>



Yes, I know that this would be more efficient if it used mod instead of base_convert, but it needs to work with integers > 32 bits.

down

fiftytoo at buckeyeexpress dot com ¶

21 years ago

I needed a function to invert a hex value, which i used for setting font colors when they were on a colored background, that way i will get a contrasting color.

Im sure there are other reasons to use this, you decide!!

<?php
function InvertColor($hex) {
  return sprintf("%06s",base_convert(($hex ^ 0xFFFFFF),10,16));
  };

print '<td bgcolor="BB2222"><font color="'.InvertColor(0xBB2222).'">Blah</font></td>';
// Prints 44dddd as the font color, which is it's opposite on the color wheel

?>

down

CJ Dennis ¶

19 years ago

Really huge numbers might be truncated at both ends.
eg:
<?php
$binary="11010101001111010001110101000100011110010110110".
"001111000010001010001111001100011010110110010010011010".
"001011010000001001011111110001010101101101011010101010".
"000100011101110010110010100111110001010010111010110011".
"001111111100011001011011001110001111110000101011010010";
print(strtoupper(base_convert($binary, 2, 16)));
?>
will output:
9E8EA23CB63C0000000000000000000000000000000000000000000000000000 (64 hex digits)
when the correct result would be:
6A9E8EA23CB63C228F31AD9268B4097F156D6AA11DCB29F14BACCFF196CE3F0AD2 (66 hex digits)
Notice that as well as the result showing '0's after B63C which you would expect it is also missing the first 6A before 9E.

down

tecdoc at ukr dot net ¶

2 years ago

Addition to the method suggested by "lindsay at bitleap dot com".

Easy way convert hex string to decimal string for 32-bit version of php
<?php
$test = '0x7000005a00000ea5';
$rrrrr = gmp_strval($test);
var_dump($test, $rrrrr);
?>
will return
//string '0x7000005a00000ea5' (length=18)
//string '8070450918794989221' (length=19)

base_convert will return 8070450918794990488

down

bryan at bryanruiz dot com ¶

14 years ago

A RFC 4648 Compliant Base32 encode.  Send me an email if you end up making this thing more efficient with bitwise operations and whatever else.

<?php

/**
 * Encode in Base32 based on RFC 4648.
 * Requires 20% more space than base64  
 * Great for case-insensitive filesystems like Windows and URL's  (except for = char which can be excluded using the pad option for urls)
 *
 * @package default
 * @author Bryan Ruiz
 **/
class Base32 {

   private static $map = array(
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', //  7
        'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 15
        'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 23
        'Y', 'Z', '2', '3', '4', '5', '6', '7', // 31
        '='  // padding char
    );
    
   private static $flippedMap = array(
        'A'=>'0', 'B'=>'1', 'C'=>'2', 'D'=>'3', 'E'=>'4', 'F'=>'5', 'G'=>'6', 'H'=>'7',
        'I'=>'8', 'J'=>'9', 'K'=>'10', 'L'=>'11', 'M'=>'12', 'N'=>'13', 'O'=>'14', 'P'=>'15',
        'Q'=>'16', 'R'=>'17', 'S'=>'18', 'T'=>'19', 'U'=>'20', 'V'=>'21', 'W'=>'22', 'X'=>'23',
        'Y'=>'24', 'Z'=>'25', '2'=>'26', '3'=>'27', '4'=>'28', '5'=>'29', '6'=>'30', '7'=>'31'
    );
    
    /**
     *    Use padding false when encoding for urls
     *
     * @return base32 encoded string
     * @author Bryan Ruiz
     **/
    public static function encode($input, $padding = true) {
        if(empty($input)) return "";
        $input = str_split($input);
        $binaryString = "";
        for($i = 0; $i < count($input); $i++) {
            $binaryString .= str_pad(base_convert(ord($input[$i]), 10, 2), 8, '0', STR_PAD_LEFT);
        }
        $fiveBitBinaryArray = str_split($binaryString, 5);
        $base32 = "";
        $i=0;
        while($i < count($fiveBitBinaryArray)) {    
            $base32 .= self::$map[base_convert(str_pad($fiveBitBinaryArray[$i], 5,'0'), 2, 10)];
            $i++;
        }
        if($padding && ($x = strlen($binaryString) % 40) != 0) {
            if($x == 8) $base32 .= str_repeat(self::$map[32], 6);
            else if($x == 16) $base32 .= str_repeat(self::$map[32], 4);
            else if($x == 24) $base32 .= str_repeat(self::$map[32], 3);
            else if($x == 32) $base32 .= self::$map[32];
        }
        return $base32;
    }
    
    public static function decode($input) {
        if(empty($input)) return;
        $paddingCharCount = substr_count($input, self::$map[32]);
        $allowedValues = array(6,4,3,1,0);
        if(!in_array($paddingCharCount, $allowedValues)) return false;
        for($i=0; $i<4; $i++){ 
            if($paddingCharCount == $allowedValues[$i] && 
                substr($input, -($allowedValues[$i])) != str_repeat(self::$map[32], $allowedValues[$i])) return false;
        }
        $input = str_replace('=','', $input);
        $input = str_split($input);
        $binaryString = "";
        for($i=0; $i < count($input); $i = $i+8) {
            $x = "";
            if(!in_array($input[$i], self::$map)) return false;
            for($j=0; $j < 8; $j++) {
                $x .= str_pad(base_convert(@self::$flippedMap[@$input[$i + $j]], 10, 2), 5, '0', STR_PAD_LEFT);
            }
            $eightBits = str_split($x, 8);
            for($z = 0; $z < count($eightBits); $z++) {
                $binaryString .= ( ($y = chr(base_convert($eightBits[$z], 2, 10))) || ord($y) == 48 ) ? $y:"";
            }
        }
        return $binaryString;
    }
}

down

bpds ¶

13 years ago

A simple function to convert an int to any base.



<?php

function intToAlphaBaseN($n,$baseArray) {

    $l=count($baseArray);

    $s = '';

    for ($i = 1; $n >= 0 && $i < 10; $i++) {

        $s =  $baseArray[($n % pow($l, $i) / pow($l, $i - 1))].$s;

        $n -= pow($l, $i);

    }

    return $s;

}



$alpha=array('a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z');

$r=rand(0, 99999999999);

echo(intToAlphaBaseN($r,$alpha));

?>

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