There may be some disagreement about the origins of LTspice, whether or not it was at all based on Berkeley's SPICE code, or if it is a complete write from scratch.? It's my understanding (based in part on something Mike Engelhardt wrote for Linear Tech) that LTspice/SwitcherCAD was not derived from Berkeley SPICE, but that the code was his own creation, based in part on the algorithms that Berkeley SPICE used, considerably enhanced by Mike's own algorithms and coding skills.? That's why it runs faster than other SPICE programs.? I think it's safe to say that so much of it has been written anew, that no or almost no Berkeley SPICE code remains.
Mike uses whatever language(s) he found helpful.? In my opinion, it's highly unlikely that he ever used FORTRAN in LTspice.? In my opinion, it's probable that he uses (at least) C and Assembly.? Comparisons with the languages used by other SPICE programs (including Berkeley SPICE) are probably meaningless.? We also know that LTspice writes some code on-the-fly.? What might that be?? I don't know, but I'm guessing machine object code.
The PC version of LTspice today appears to call some Microsoft runtime functions.? That observation is based on feedback about some of the errors that happen, as well as the numeric results one gets when numbers overflow (e.g., 1.#QNAN, 1.#IND, 1.#INF).
LTspice's name originally did not even include the acronym "SPICE".? It was "SwitcherCAD" -- with "LTspice" becoming a nickname.? At some point, Mike gave in and officially renamed it to LTspice.
