Thank you for this bug report. To properly diagnose the problem, we
need a short but complete example script to be able to reproduce
this bug ourselves.

A proper reproducing script starts with <?php and ends with ?>,
is max. 10-20 lines long and does not require any external
resources such as databases, etc. If the script requires a
database to demonstrate the issue, please make sure it creates
all necessary tables, stored procedures etc.

Please avoid embedding huge scripts into the report.

<?php
  $from = "C:\myBigFile.mp4"; // Needs to be a big ile, like 5GB or 6GB
  $to = "C:\myBigFile_COPY.mp4";
  copy($from, $to);
?>

Copies exactly 1GB. Affects other functions like stream_copy_to_stream() as well.

There may be an existing bug report for this problem.

This is a Windows only issue, and is because we're not properly
retrieving the file size when mmapping.  After this is fixed, on
32bit systems files up to 4294967295 bytes can be copied; 64bit
systems practically have no limit.