Typecasting on bitwise operators - php

Question

Can anyone explain why I have different output for the two bitwise operation in the code below?
According to the php documentation at http://php.net/manual/en/language.operators.bitwise.php, $value should typecast to an integer:
Both operands and the result for the << and >> operators are always treated as integers.
My code:
$value = 4294967295;
echo 'value is float: ' . (($value >> 32 - 1) & 1); //OUTPUT: value is string: 1
$value = '4294967295';
echo 'value is string: ' . (($value >> 32 - 1) & 1); //OUTPUT: value is string: 0
Does typecasting for the second operation not work, since unsigned integers aren't supported and the operation is performed on the ASCII values of the characters?
If so, why does it work with the float value?
My code works fine with the float value, so I have no real problem, but I would like to understand what is happening. It took me a while to figure out, where my code didn't behave as expected.
I use php version 5.4.19 on Windows 7 x64 (for testing).

Answer 1

This is an explanation of what appears to be happening. PHP 5.3.18, windows XP, 32 bit.
The code:
$value = 4294967295; // This is a 'float'
$vint = (int) $value; // this becomes -1 as an integer.
// shows the types and values
var_dump($value, $vint, dechex($vint));
echo 'value is float: ' . (($value >> 32 - 1) & 1); //OUTPUT: value is string: 1
The output:
float 4294967295
int -1
string 'ffffffff' (length=8)
value is float: 1
Note that the 'float' is converted to integer -1, which is all bits on. Hence the output result when shifted.
Now lets look at the other result:
The code:
$value = '4294967295'; // is treated as positive?
var_dump($value, dechex($value));
echo 'value is string: ' . (($value >> 32 - 1) & 1); //OUTPUT: value is string: 0
The output:
string '4294967295' (length=10)
string '7fffffff' (length=8)
value is string: 0
The interesting point here is that the 'sign' bit is 'off' when converted to an integer. This explains the output when shifted.