Convert 64 bit Integer hex string to 64 bit decimal string on 32 bit system
<p>What is a simple way to convert a 64 bit integer encoded as a hex string to a decimal string on a 32 bit system. It needs to be the full value, it can not be in scientific notation or truncated :/</p>

<p>"0c80000000000063" == "900719925474099299"</p>

<p>"0c80000000000063" != 9.007199254741E+17</p>

<p>PHP's base_convert() and hexdec() don't do the job right.</p>
