A BrainF*ck-ish compiler in C

-ish because I removed the input functionality from the compiler. And, the compiler does not support nested loops

I've been recently reading up on compilers and how they work. Although this doesn't use most of the things I've learned about (the lexical and parser things), I thought it would be fun to try create a brainf*ck compiler, rather than an interpreter.

bfc.c

```
#include

static int i;
static char *code; // these two as static so get_amt_to_change can easily interact

int get_amt_to_change(char c); // so the compiler doesn't write (ie) add di, 1 ten times

int main(int argc, char **argv) {
code = argv[1];
puts("xor di, di\n"
"setup_loop:\n"
"mov byte [tape + di], 0\n"
"add di, 1\n"
"cmp di, 101\n"
"jne setup_loop\n"
"xor di, di"); // sets up the tape with all 0's
int loop_count = 0; // to keep track of asm subroutines for [ and ]
for(i = 0; code[i] != '\0'; i++) {
switch(code[i]) {
case '+':
printf("add byte [tape + di], %d\n", get_amt_to_change('+'));
break;
case '-':
printf("sub byte [tape + di], %d\n", get_amt_to_change('-'));
break;
case '>':
printf("add di, %d\n", get_amt_to_change('>'));
break;
case '<':
printf("sub di, %d\n", get_amt_to_change('<'));
break;
case '.':
puts("mov ah, 0Eh\n"
"mov al, byte [tape +di]\n"
"int 10h");
break;
case '[':
printf("cmp byte [tape + di], 0\n"
"je end_loop%d\n"
"start_loop%d:\n", loop_count, loop_count);
break;
case ']':
printf("cmp byte [tape + di], 0\n"
"jne start_loop%d\n"
"end_loop%d:\n", loop_count, loop_count);

You need to enlarge tape because your initialization zeroes 101 bytes.

section .bss
 tape resb 101

When in graphics mode, the teletype function uses the BL and BH registers as arguments.

mov  bx,0007h ;Display page 0 and Color 7
 mov  ah, 0Eh
 mov  al, byte [tape +di]
 int  10h

When in text mode, the teletype function uses the BH register as an argument.

mov  bh,0     ;Display page 0
 mov  ah, 0Eh
 mov  al, byte [tape +di]
 int  10h

You can optimize the setup code by iterating backwards. It shaves off 2 instructions! It too will leave DI=0.

mov  di, 101
setup_loop:
 sub di,1
 mov  byte [tape + di], 0
 jnz  setup_loop

I don't know if you would care but the code for [ ] by itself produces an infinite loop if the byte at [tape + di] is anything but zero.

StackExchange Code Review Q#83600, answer score: 3