PHP 4 handles number-constants smartly. I.e., when a number is out of range of integers, it will be auto-converted to float.

var_dump(0x80000000) -> float(2147483648)

While | requires int-arguments, and because it cannot convert float(2147483648) to int, it will take MAX_INT instead.

That abs(MINIMAL_INT) bug, is a bug which I fixed yesterday (coincidence...)

The 0x80000000 | 0; : apparently 

(int) 2147483648.0 => -2147483648
This IS a bug, because it should have been INT_MAX (2147483647)

I'm currently trying to sort that out. By the way, do not put multiple bugs in one report.

I wan't really clear on this one: PHP _does not support unsigned ints_

Generally, it support integers from -2147483648 to 2147483647

From http://www.docs.intranet.giga/php/language.types.integer.html:

From floating point numbers
When converting from float to integer, the number will be rounded towards zero. 

If the float is beyond the boundaries of integer (usually +/- 2.15e+9 = 2^31), the result is undefined, since the float hasn't got enough precision to give an exact integer result. No warning, not even a notice will be issued in this case! 

(I should have known, I wrote that myself...)
So there this is "feature", AKA documented bug. Feel free to open a feature request to get that changed...

In the manual it should be better noted in integers -> big number section that it goes for hex too. I'll do that in a minute. 

Status -> Closed (for the abs() bug)

This url will also work outside "Jeroen's intranet" ;-)

http://www.php.net/manual/en/language.types.integer.php