In one of my programs, which is written in C, I use an editor component called RAEdit, written in 32-bit assembly. Link: http://sourceforge.net/p/fbedit/code/HEAD/tree/SimEd/RAEdit/

I need to convert the program to 64-bit. The program itself is written in C, so it's not a problem, but is there some way to (semi)automatically convert RAEdit to 64-bit?

For what it's worth, the code heavily uses macros, such as if, while, invoke, which I believe should simplify the conversion. Typical source file from the codebase: http://sourceforge.net/p/fbedit/code/HEAD/tree/SimEd/RAEdit/Edit.asm

Any help is appreciated!

First of all I believe that the source code your are using is using MASM not FASM syntax. So if you are going to use it with FASM you need to convert the syntax first.

Secondly I'm not aware of any automatic conversion tools from 32 to 64 bit assembly language. The invoke macro has to be handle differently since calling convention is different both for Win32 and Win64 - consult MSDN for further explanation but besides using R* registers you also need to provide a so call shadow space.

Also SEH and other system structures are different (and under different addresses). Since you are using C the compiler may take care of exception handling for you but nevertheless if your code is using segment registers to access system structures if will fail.

So to make long story short without peeking much into the sources you provided, there is no (semi)automatically method of converting it to x64 I believe.