asked on

Delphi->PHP Conversion .

I have a need for some Integer to base36 conversions.

I have the code in Delphi but need a PHP version now.

Here is the Delphi code:

const XX = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ' ;
Function Base36ToInt (const S: string): Int64;
var i: integer;
begin
Result := 0;
For i := 1 to length(S) do
Result := Result * 36 + Pred(Pos(UpCase(S[i]), XX)) ;
end;

Function IntegerToBase36 (I: Int64): string;
begin
Result := '';
Repeat
Result := XX[Succ(I mod 36)] + Result ;
I := I div 36;
Until I=0;
end;

Using base_convert DOES NOT work the same and returns a
different result. I need the code above converted directly.

Here is sample data:

Integer passed: 5555444433331111
String Result: 177XYGYLBFLZ4

Using this PHP code:
function base36toint($s){
$x = base_convert($s, 36, 10);
return $x;
}

function inttobase36($s) {
$x = base_convert($s, 10, 36);
return $x;
}

results in this: 1ip8nxua3s7

Another developer using the exact same PHP code
gets a different result than I, why?

_GeG_

either your example or your delphi code is wrong, I checked, both my custom conversion and base_convert return the same result:
function Base36ToInt ($s){
      static $x=array('1'=>1, '2'=>2, '3'=>3, '4'=>4, '5'=>5, '6'=>6, '7'=>7, '8'=>8, '9'=>9,
             '0'=>0, 'a'=>10, 'b'=>11, 'c'=>12, 'd'=>13, 'e'=>14, 'f'=>15, 'g'=>16, 'h'=>18,
             'i'=>18, 'j'=>19, 'k'=>20, 'l'=>21, 'm'=>22, 'n'=>23, 'o'=>24, 'p'=>25, 'q'=>26,
             'r'=>27, 's'=>28, 't'=>29, 'u'=>30, 'v'=>31, 'w'=>32, 'x'=>33, 'y'=>34, 'z'=>35);
      $r=0;
      $s=strtolower($s);
      for ($i=0;$i<strlen($s);$i++){
            $r=bcadd( bcmul($r, 36), $x[$s{$i}]);
      }
      return $r;
}
echo Base36ToInt('177XYGYLBFLZ4')."\n";
echo base_convert('177XYGYLBFLZ4', 36, 10);

result:
5688775099731057664
5688775099731058624

_GeG_

ooops, now I see they are not the same :(
Must be a rounding error in base_convert, how ugly!

_GeG_

ok, a little more testing:
on linux php 4.3.8 there is no error
on windows php 5.0 there is a rounding error, very ugly!

ASKER CERTIFIED SOLUTION

Marcus Bointon

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Eddie Shipman

ASKER

Squinky:
Using your code:
<?PHP
/**
* Convert a number (as a string) in base 10 to any base
*
* e.g. dec2base('32', 16) => '20';
* Uses BCMath extension, so number can be as big as you like
* @param string $value A number in base 10, expressed as a string
* @param integer $base The base to convert to
* @param mixed $digits Optional string representing the characters used in the numbering system
*/
function dec2base($dec, $base, $digits = FALSE) {
if($base < 2 or $base > 256) die("Invalid Base: .$base\n");
bcscale(0);
$value = '';
if(!$digits) $digits = digits($base);
while($dec > $base - 1) {
$rest = bcmod($dec,$base);
$dec = bcdiv($dec,$base);
$value = $digits[$rest].$value;
}
$value=$digits[intval($dec)].$value;
return (string) $value;
}

/**
* Convert a number (as a string) in any base to base 10
*
* e.g. base2dec('20', 16) => '32';
* Uses BCMath extension, so number can be as big as you like
* @param string $value A number in any base, expressed as a string
* @param integer $base the base that this number is in
* @param mixed $digits Optional string representing the characters used in the numbering system
*/
function base2dec($value, $base, $digits = FALSE) {
if($base < 2 or $base > 256) die("Invalid Base: .$base\n");
bcscale(0);
if($base < 37) $value = strtolower($value);
if(!$digits) $digits = digits($base);
$size = strlen($value);
$dec = '0';
for($loop=0; $loop < $size; $loop++) {
$element = strpos($digits, $value[$loop]);
$power = bcpow($base, $size-$loop-1);
$dec = bcadd($dec, bcmul($element, $power));
}
return (string) $dec;
}

/**
* Return a string containing chars to use in a given base's numbering system
*
* e.g. digits(16) => '0123456789abcdef'
* @param integer $base
* @return string
*/
function digits($base) {
if($base > 64) {
$digits = '';
for($loop=0; $loop < $base; $loop++) {
$digits .= chr($loop);
}
} else {
$digits = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_';
}
$digits = substr($digits, 0, $base);
return (string) $digits;
}

$s = "5555444433331111";
echo "Input#: ".$s;

$encrypt = dec2base($s,36);
echo " <br>Encrypted: ".$encrypt;

$decrypt = base2dec($encrypt,10);
echo " <br>Decrypted: ".$decrypt;

?>

Here are the results:
Input#: 5555444433331111
Encrypt: 1ip8nxua3s7
Decrypt: 10080000307

Did I do something wrong???

Marcus Bointon

yes:

$decrypt = base2dec($encrypt, 36);

I just happen to have made these functions do conversions to and from base-10, rather than between arbitrary bases. base2dec always produces a base-10 number, but you need to tell it what the input base is. You've got a weird result because you told it that '1ip8nxua3s7' is a base-10 number, and it doesn't check that what you submit is actually a valid number in that base.

Marcus Bointon

Also, you may want to change the order of upper and lower case letters in the digits function to retain compatibility with your Delphi function - I chose to make lower case numbers represent smaller numbers.

Eddie Shipman

ASKER

I completely took out the capital letters and the - and _, we will never be using a negative number.

I used other routines for the Delphi conversion (see below).

Many thanks.

Delphi code used:
function Base36ToInt(const S: String): Int64;
var
i: integer;
begin
Result := 0;
for i := 1 to Length( S ) do
begin
if S[i] in ['0'..'9'] then
begin
Result := Result * 36 + ( Ord( S[i] ) - Ord( '0' ) );
end
else
begin
Result := Result * 36 + ( Ord(S[i] ) - Ord( 'a' ) + 10);
end;
end;
end;

function IntegerToBase36 (I: Int64): String;
var
N: Int64;
M: integer;
begin
Result := '';
repeat
M := I mod 36;
if M < 10 then
begin
Result := Char( Ord( '0' ) + M ) + Result;
end
else
begin
Result := Char( Ord( 'a' ) + M - 10 ) + Result;
end;
I := I div 36;
until I = 0;
end;

Delphi-&gt;PHP Conversion .

Delphi->PHP Conversion .