/* dontmove: a MOV machine for archival.
 *
 * First version of this C was written from 00:00 to 00:33,
 * at which point I was able to write and run a couple of "hello world"s.
 * This is slightly longer than the 22 minutes it took me to write a Brainfuck
 * interpreter.  The code is almost exactly the same size, except that this
 * one uses stdio and has some minimal file error handling.
 * It took me another 20 minutes to get an incrementing loop written and 
 * debugged.  I still haven't tested procedure calls, conditionals,
 * and comparisons, but I'm pretty sure they'll work.
 */
#include <stdio.h>
#include <stdint.h>

typedef uint32_t cell;
enum { PROGSIZE = 65536, MEMSIZE = 1048576 }; 

char program[PROGSIZE];
size_t proglen;
cell accumulator, subtractor, memory[MEMSIZE], pc;

typedef int bool;

bool read_program(char *filename) 
{
    FILE *in = fopen(filename, "r");
    if (!in) {
        perror(filename);
        return 0;
    }

    proglen = fread(program, 1, PROGSIZE, in);

    fclose(in);

    if (!proglen) {
        perror(filename);
        return 0;
    }
    return 1;
}

#define IF break; case
#define ELSE break; default

void read_memory(cell address) 
{
    switch(address) {
    IF 0: accumulator = getchar();  /* A */
    IF 1: accumulator = subtractor; /* B */
        /* XXX bounds check? */
    IF 2: read_memory(memory[3]);   /* C */
    IF 4: accumulator = pc;         /* E */
    ELSE: accumulator = memory[address];
    }
}

void write_memory(cell address)
{
    cell tmp;
    
    switch(address) {
    IF 0: putchar(accumulator);      /* a */
    IF 1: subtractor -= accumulator; /* b */
        /* XXX bounds check? */
    IF 2: write_memory(memory[3]);   /* c */
    IF 4:                            /* e */
        tmp = accumulator;
        accumulator = pc;
        pc = tmp;
    ELSE: memory[address] = accumulator;
    }
}

int main(int argc, char **argv)
{
    if (!read_program(argv[1])) return 1;
    
    while (pc < proglen) {
        /* printf("[%d]", pc); fflush(stdout);  */
        char insn = program[pc++];
        if ('A' <= insn && insn <= 'Z') {
            read_memory(insn - 'A');
        } else if ('a' <= insn && insn <= 'z') {
            write_memory(insn - 'a');
        } else if ('0' <= insn && insn <= '9') {
            accumulator = accumulator * 10 + insn - '0';
        } else if ('<' == insn) {
            accumulator = (accumulator & 0x80000000 ? 0xFfffFfff : 0);
        }
        /* else, no op. */
    }

    return 0;
}