On 1/12/2014 10:25 AM, cameron7(at)gmail(dot)com wrote:
> I guess I'll reply with my own solution. Turns out there are 2 separate issues here.
>
> 1) the "signed" bit needs to be flipped back to 0 before converting to int. This is because it appears the conversion from base 2 to base 10 will always assume the end value is positive.
> 2) Because of this, the rest of the bits need to be flipped.
>
True. base_convert
> So I added 2 arguments to the function, one will tell us if we're supposed to be checking for a "signed bit", and the other will tell us if we need to flip bits.
>
> As you'll see I'm still off by 1 in the end result, but I'm sure that's just in the details.
>
That's because when you use 2's compliment, you need to flip the bits
and add one.
>
> I hope you'll all agree, this is really ugly, but seems to work :)
>
> <?php
>
> $i64 = -8223372036854775807;
>
> echo "PACKING: ".$i64.PHP_EOL;
>
> list(,$binary) = getBinaryString($i64, 64);
>
> list(,$i64a) = unpack('N', pack('N', base_convert(substr($binary, 0, 32), 2, 10)));
> list(,$i64b) = unpack('N', pack('N', base_convert(substr($binary, 32, 32), 2, 10)));
>
> list($flag,$i64c)= getBinaryString($i64a, 32, true, true);
> list(,$i64d) = getBinaryString($i64b, 32, false, true);
>
> $unpack = base_convert($i64c.$i64d,2,10);
> $unpack *= $flag ? -1 : 1;
>
> echo "UNPACKED: ".$unpack.PHP_EOL;
>
> function getBinaryString($packed,$bits,$check_signed = false, $flip = false){
> $a = 0x01;
> $binary = '';
> for($x=0; $x<$bits; $x++){
> $binary .= (int)(bool)($a & $packed);
> $a = $a << 1;
> }
> $signed_flag = false;
> if($check_signed && substr($binary,$bits-1,1) === '1'){
> $signed_flag = true;
> }
> if($flip){
> for($x=0;$x<strlen($binary);$x++){
> $binary[$x] = $binary[$x] === '1' ? '0' : '1';
> }
> }
> if($signed_flag){
> $binary = substr($binary,0,$bits-1).'0';
> }
> return array($signed_flag, strrev($binary));
> }
>
I've seen worse :)
However, you might want to check some other functions. The gmp_xxx
functions will work on longer numbers; so will the BCD functions.
There are some suggestions and links under base_convert() in the online
documentation at http://us1.php.net/manual/en/function.base-convert.php.
Of course, if you're on a shared host and can't get them to install the
libraries for you, you're out of luck.
--
==================
Remove the "x" from my email address
Jerry Stuckle
jstucklex(at)attglobal(dot)net
==================
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