The sheer size of the thing is a big problem.<p>Getting ~100KLOC of C++ compiling on a &quot;new&quot; compiler has been something that&#x27;s taken me a few days before.  Not too unreasonable.<p>100MLOC is literally 1000x the size - which extrapolating from &quot;a few days&quot; would mean it&#x27;d take me 8-14 <i>years</i> to fix up on my own were I to do it by hand.  Or more realistically, the pace of change&#x2F;growth on a codebase of that size probably outstrips my ability to convert it.<p>So now even a simple straightforward task such as fixing up technically nonstandard C++ syntax to standard C++ that multiple compilers will happily accept, is a task requiring either automated code modifications (scary!) or a large coordinated team effort.  If 100 people working together are, optimistically, 100x as efficient as me alone - i.e. there&#x27;s no overhead in terms of coordination and planning - it will still take them around a month to do the job via brute force.