Is there an ELI5 for this? How could something so small possibly be an 8080 emulator?
> If you're looking for information about the Mexican scientist Oscar Toledo Esteva, then please go to the History page of the Familia Toledo organization site.
https://nanochess.org/author.html
Odd that he doesn't mention the "scientist" people may be looking for is his father, but everything else lines up.
Most of the instructions are changing registers in various ways, which is pretty simple. The Appendix A has all of them: https://altairclone.com/downloads/manuals/8080%20Programmers...
https://www.ioccc.org/1992/1992.tar.bz2
You need to edit the CFLAGS (or just comment that line), and by using gcc or even tcc will work fine.
unsigned char memory[65536];
int reg[8];
int main(void)
{
int pc = 0;
/* In this point you read something into memory */
while (1) {
instruction = memory[pc];
if (instruction == 0x76) break; /* HLT */
pc = (pc + 1) & 0xffff;
if ((instruction & 0xc0) == 0x40) /* Handle MOV r,r (opcodes 0x40-0x7f) */
reg[(instruction >> 3) & 7] = reg[instruction & 7];
}
return 0;
What it does? It simply reads each instruction from memory (PC is the Program Counter), and increments PC continuously limiting it to 16-bit.
It does a comparison for each possible instruction, for this example I only handled the most basic one of 8080 (MOV r,r) and HLT, but this is already 64 cases of the 256 possible!
Then I added iteratively chunks of opcodes to emulate and used language C macros to reduce the code size. For example, there is #define d(e) to join two 8-bit registers into a 16-bit value, and #define Q to read the accumulator.
In the end, to stay inside the size limit of the IOCCC, I removed the tree of 'if' statements and replaced it with a tree of trinary operators ?: (a way of doing 'if' inside an expression) and this is what the macros C and S does.