how to determine if a number is greater than 32 bits?

sneakyimp

ok...so 2 to the 32nd power is 4294967296

does that mean any number larger than that is greater than 32 bits? is 4294967296 actually the break point or does the whole 1's complement / 2's complement thing come in to play?

Weedpacket

If it doesn't fit in an integer, PHP stores it as a double.

$huge = 12345678901234567890;
echo $huge.' '.gettype($huge);
$notsohuge = 123456789;
echo "\n";
echo $notsohuge.' '.gettype($notsohuge);
$downcast = (int)$huge;
echo "\n";
echo $downcast.' '.gettype($downcast);

Mess with that and the other typing functions and see what comes up.

Two's-complement notation is for representing negative numbers.

sneakyimp

unfortunately, i'm using actionscript (macromedia flash). i'm trying to replicate the serialize() function in flash so I can easily shoot arrays and stuff back and forth .

so i won't be able to use gettype(). i've posted the macromedia forum, i was just hoping maybe somebody here could tell me what the criteria is for a double.

sneakyimp

does anyone know how to go about determining if a given number is a double (8 byte number) or a single (4 byte number) without using the very useful gettype() function?

Weedpacket

This question is highly language-specific; some languages (or at least, some language implementations) don't store numbers as C-like ints or doubles at all. In PHP's case (on a 32-bit machine, at least), the largest number expressible as an integer is 2^31-1 (i.e 2147483647). Adding 1 to this in PHP will give you 2147483647, stored as a double, while C will tell you (assuming you're using a signed int and not an unsigned one) that the answer is an int with a value of -1, since 10000000000000000000000000000000 binary is the two's complement representation of -1 (in a thirty two bit environment). In fact, PHP will also tell you that 1<<31 is equal to -1, because it will take the 1, shift it left thirty-one places and get the above bit pattern.

sneakyimp

aha. thanks for the info!

do you think that it would be a bad idea to serialize all my numbers from flash as doubles? someone on the macromedia forum told me this:

Anything that is a 'Number' type in ActionScript is a double.

I'd like to make my actionscript serialize function as accurate as possible.

sneakyimp

i just re-read your post...do you mean to say that in PHP if i type this:

echo 2147483647++

i get
2147483647

sneakyimp

i've done some experiments...looks like when you serialize, PHP uses these critieria for numbers:

integers less than or equal to 2147483647 are SINGLES (serialize with indicator i).
integers greater than or equal to 2147483648 are DOUBLES (serialize with indicator d).
* decimals with a fractional value of even a single digit are serialized as DOUBLES (e.g., 1.1 is a double)

BUT CHECK OUT THIS WACK STUFF...serializing this array...this code:

$arr[0] = 1;
$arr[1] = 2;
$arr[2] = "foo";
$arr[3] = 12343434874.348373872;
$arr[4] = 2147483647;
$arr[5] = 1.1;
$arr[6] = 2147483648;
$arr[7][0] = "first sub array";
$arr[7][1] = "second sub array";

echo "value is " . $arr[3] . "<BR>";
echo(serialize($arr));

returns this:

value is 12343434874.348
a:8:{i:0;i:1;i:1;i:2;i:2;s:3:"foo";i:3;d:12343434874.3483734130859375;i:4;i:2147483647;i:5;d:1.100000000000000088817841970012523233890533447265625;i:6;d:2147483648;i:7;a:2:{i:0;s:15:"first sub array";i:1;s:16:"second sub array";}}

what the heck?? first off, where'd my digits go (i've started another post to ask this question). secondly, WHERE did all those extra digits come from in the serialized form?? since when does 1.1 equal 1.100000000000000088817841970012523233890533447265625???

Weedpacket

Oh, just thought I'd mention; the numbers would probably get transported from Flash to PHP as text - to be exact, a sequence of decimal digits. With maybe a decimal point. They'll be stored as strings until you do something arithmetical with them, at which point PHP will convert them to its reckoning of an appropriate numeric type (if it looks like an integer - no decimal point - PHP will try and store it in an integer if it will fit; it will use a double otherwise).

sneakyimp

thanks for info!

just to be clear, that code I typed is all PHP. I read the other thread...how distressing!

forget everything from school -- you are programmer, 
and here 2.1*3.6=7.559995 
but sometimes (2.1*3.6==7.559995)!=true 
this is the world with no rules after point -- this is computer.

I do think I agree with edrugtrader....if you use == as a comparison, it should maybe use your current ini's precision settings for the comparison. i also found out that flash does some truncating...i'm working on figuring that out now as well.

this is all most unsettling 😉