The clue to vdbe.c is this comment:
That switch statement is read by a script that produces two other files, opcodes.h & .c. The main file, .h, is a list containing 150 #defines. So, yeah, I guess it really is a massive switch statement!What follows is a massive switch statement where each case implements a separate instruction in the virtual machine.
All I can say is: Wow!
No wonder I couldn't find any rewrites*! It would be like repainting the Sistine Chapel. With a toothbrush.
*I was curious. So I poked around and found lots of wrappers, but no rewrites. Considering the amount of time that has gone into the original, and the licensing (open source, public domain) - you'd need a pretty strong business case to rewrite it. Mind you, it's very fast and capable and simply works. Why mess with success like that?