The size of an integer is platform-dependent, although a maximum value
of about two billion is the usual value (that's 32 bits signed). 64-bits
platforms usually have the maximum value of about 9E18. PHP does not
support unsigned integers. Integer size can be determined using the
constant PHP_INT_SIZE, and maximum value using the constant PHP_INT_MAX
since PHP 4.4.0 and PHP 5.0.5.