PHP 8.1.31 Released!

    bindec

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

    bindec — 2 進数 を 10 進数に変換する

    説明

    bindec(string $binary_string): int|float

    引数 binary_string により指定された 2 進数と等価な 10 進数を返します。

    bindec() は、2 進数を int に変換します。 サイズの問題により、必要に応じて float となることもあります。

    bindec() は、すべての binary_string 値を符号なし整数として扱います。 これは、bindec() が最上位ビットを 符号ビットではなく別の桁とみなすからです。

    パラメータ

    binary_string

    変換したい 2 進数文字列。 binary_string に無効な文字を与えても、静かに無視されます。 PHP 7.4.0 以降では、無効な文字を与えることは推奨されません。

    警告

    このパラメータは文字列でなければなりません。 他のデータ型を使用すると、予期せぬ結果となります。

    戻り値

    binary_string を 10 進に変換した値を返します。

    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 bindec() の例

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

    echo     bindec('111');
    ?>

    上の例の出力は以下となります。

    51
51
7

    例2 bindec() が入力を符号なし整数として処理する例

    <?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";
    }
    ?>

    上の例の 32 ビットマシンでの出力は、このようになります。

    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

    上の例の 64 ビットマシンでの出力は、このようになります。

    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

    注意

    注意:

    この関数は、プラットフォームの int 型に収まらない大きな数も変換できます。 その場合、結果は float で返します。

    参考

    • decbin() - 10 進数を 2 進数に変換する
    • octdec() - 8 進数を 10 進数に変換する
    • hexdec() - 16 進数を 10 進数に変換する
    • base_convert() - 数値の基数を任意に変換する

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    ＋add a note

    User Contributed Notes 10 notes

    up
    7
    info at rickdg dot nl
    14 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
    3
    martin at punix dot de
    21 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
    3
    gwbdome at freenet dot de
    20 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
    Nitrogen
    15 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
    1
    alan hogan dot com slash contact
    17 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
    0
    patrick dot boens at latosensu dot be
    12 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
    -1
    mashematician at gmail dot com
    16 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');

    ?>
    up
    -1
    jpfstange at gmail dot com
    8 years ago
    <?php

    //binfloat (For single precision floating point numbers)
    //IEE754
    //https://en.wikipedia.org/wiki/Single-precision_floating-point_format

    function binfloat(Array $num){

    $sign = $num[0] ? 1 : -1; //1 bit
    $exponent = pow(2,bindec(implode('',array_slice($num,1,8)))-127);
    $fraction = array_slice($num,9,count($num)); //23 bits
    $fracSum = 1;

    for(    $i=0;$i<23;$i++){

    $fracSum += $fraction[$i] * pow(2,-1-$i);

    }

    return     $fracSum*$exponent;

    }

    $num = isset($_GET['num']) ? $_GET['num'] : '00111110001000000000000000000000';

    if(    strlen($num)<32){

    echo     "Invalid binary number $num\n";
    exit(    1);

    }

    $num = str_split($num);

    echo     sprintf('Num is: [%s]%s',implode('',$num),"\n");
    echo     sprintf('Result is: %s%s',binfloat($num),"\n");
    up
    -1
    flashpack at gmail dot com
    16 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     $result ;
    }
    ?>
    up
    -3
    nodarinodo at mail dot ru
    15 years ago
    <?php
    // bindecfunc :)))) I think it works well too :)
    function bindecc($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;
    }
    ?>
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