Description
number 
hexdec ( string hex_string )
     Returns the decimal equivalent of the hexadecimal number
     represented by the hex_string argument.
     hexdec() converts a hexadecimal string to a
     decimal number. The largest number that can be converted is
     7fffffff or 2147483647 in decimal.
     As of PHP 4.1.0, this function can also convert larger numbers. It returns
     float in that case.
    
     hexdec() will ignore any non-hexadecimal 
     characters it encounters.
     
Example 1. hexdec() example 
<?php var_dump(hexdec("See")); var_dump(hexdec("ee")); // both print "int(238)"
  var_dump(hexdec("that")); // print "int(10)" var_dump(hexdec("a0")); // print "int(160)" ?>
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     See also dechex(),
     bindec(),
     octdec() and
     base_convert().