Algorithm-how does php convert a 20-bit 62-hexadecimal string back to a 10-hexadecimal string?

Php converts a 20-bit 62-digit string to a 10-digit string. At present, {code...} can be used to convert a super-long decimal integer to the 62 hexadecimal notation. However, due to system restrictions, it will become a number such as 9.9999999991447E + 27. An algorithm is required to convert the super-long 62 hexadecimal into... php to convert a 20-bit 62 hexadecimal string back to the 10 hexadecimal string.
Currently

    function dec62($n) {        $base = 62;        $index = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';        $ret = '';        for($t = floor(log10($n) / log10($base)); $t >= 0; $t --) {            $a = floor($n / pow($base, $t));            $ret .= substr($index, $a, 1);            $n -= $a * pow($base, $t);        }        return $ret;    }

The super-long decimal integer can be converted to the 62-digit system. However, due to system restrictions, it will become9.9999999991447E+27Such a number.
An algorithm is required to convert the super-long 62 hexadecimal string back to the 10 hexadecimal string.
You can use the following number to test
9999999999144705880199999999999

Reply content:

Php converts a 20-bit 62-digit string to a 10-digit string.
Currently

    function dec62($n) {        $base = 62;        $index = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';        $ret = '';        for($t = floor(log10($n) / log10($base)); $t >= 0; $t --) {            $a = floor($n / pow($base, $t));            $ret .= substr($index, $a, 1);            $n -= $a * pow($base, $t);        }        return $ret;    }

The super-long decimal integer can be converted to the 62-digit system. However, due to system restrictions, it will become9.9999999991447E+27Such a number.
An algorithm is required to convert the super-long 62 hexadecimal string back to the 10 hexadecimal string.
You can use the following number to test
9999999999144705880199999999999

Use BCMath for addition, subtraction, multiplication, and division of any precision.

function base62to10($n){    $index = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';    $n = strval($n);    $len = strlen($n);    $result = 0;    $base = 1;    for ($i = $len-1; $i >= 0; $i--) {        $char = $n[$i];        $d = strpos($index, $char);        assert($d !== false);        $result = bcadd($result, bcmul($d, $base));        $base = bcmul($base, 62);    }    return $result;}echo base62to10('9999999999144705880199999999999'),"\n";

First, the author's algorithm is incorrect, Because I tested dec62 () using the numbers 9999999999144705880199999999999 and 9999999999144705880199999999998 and found that the output results were the same.
I saw the great algorithm in the php Manual (BCMath support is required ):

    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
  

Usage:
1. Convert decimal to 62 hexadecimal

echo convBase('9999999999144705880199999999999','0123456789','0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');

2. Convert 62 to decimal

echo convBase('3nLqycbr6ZQsN1JJYX','0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ','0123456789');

It supports any form of hexadecimal conversion, see the http://php.net/manual/en/function.base-convert.php