I can not see any problems with memory leaks in these functions. Run this script in SciTE:
#include <A3LLibrary.au3>
GUICreate("Test", 400, 300)
GUISetState()
do
$fFloat = _Lib_IntToFloat(1234 )
$iInt = _Lib_FloatToInt(123.4)
until GUIGetMsg() = $GUI_EVENT_CLOSE
Pull up task manager and watch the memory consumption for AutoIt3.exe. It doesn't budge. Can you can send me a small, working script with the original functions that causes the problems you are seeing?