Update README.md to reflect this fork

README.md

@@ -1,14 +1,62 @@
-c4 - C in four functions
-========================
+c4 - A self-contained C Compiler and VM that can run itself
+===========================================================
 
-An exercise in minimalism.
+C4 is Robert Swierczek's tour-de-force exercise in minimalism, a four
+function C-subset compiler that can run itself.  This fork aims to
+evolving it a bit, forgoing the "four function" constraint, but
+keeping the self-compiling and self-contained property.
+
+Wishlist
+--------
+
+- Merge the switch + struct work into c5 (the c4 branch that adds an
+  intermediate AST)
+
+- Enable a standalone VM (currently host addresses are embedded into
+  the instruction stream).  Make the VM byte-code based, increasing
+  the code density substantially.
+
+- Migrate to a more efficient execution model.  The current stack
+  machine is rather inefficient; for example `x += y` (which both are
+  local variables) are translated into
+
+```
+LEA -6; PSH; LEA -6; LI; PSH; LEA -3; LI; ADD; SI
+```
+  where we really just need something like
+```
+ADD -6, -3`
+```
+  (Note, this looks a lot like a register machine, but the "registers"
+  here are stack allocated variables).
+
+- Switch statements should be table-lookup based.
+
+- Expand the language in the direction of C99, notably adding locals
+  with initialization.
+
+
+Tricks
+------
+
+Robert deploys a range of marvelous tricks to keep this simple and
+small.  An incomplete list includes:
+
+- Tokens are in operator precedence order which simplifies the
+  precedence-climbing recursive descent parser.
+
+- Lvalue addresses are handled by undoing the last load (this only
+  applies to c4 as with the AST something different is done).
+
+Usage
+=====
 
 Try the following:
 
     gcc -o c4 c4.c
     ./c4 hello.c
     ./c4 -s hello.c
-    
+
     ./c4 c4.c hello.c
     ./c4 c4.c c4.c hello.c
 

c4.c

@@ -4,7 +4,8 @@
 // if, while, return, and expression statements
 // just enough features to allow self-compilation and a bit more
 
-// Written by Robert Swierczek
+// Written by Robert Swierczek, 2014-2019
+// Tweaked by Tommy Thorn, 2023
 
 #include <stdio.h>
 #include <stdlib.h>