brainfuck simple impl in C

bf.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static char* instruction = NULL;
static size_t instruction_size = 0;

#define DEFAULT_DATA_SIZE 30000

static char data[DEFAULT_DATA_SIZE];

int load_instruction_from_stream(FILE* file) {
	size_t iread = 0;
	char buffer[1024];

	while (1) {
		size_t len = fread(buffer, sizeof(buffer[0]), sizeof(buffer) / sizeof(buffer[0]),
				   file);
		if (len == 0) { // EOF or error
			break;
		}

		instruction_size += len;
		instruction = realloc(instruction, instruction_size);
		if(!instruction) {
			fprintf(stderr, "memory exhausted on ip.\n");
			abort();
		}

		memcpy(instruction + iread, buffer, len);
		iread += len;
	}

	return (ferror(file)) ? -1 : 0;
}

int load_instruction_from_path(const char* filename) {
	FILE* file = fopen(filename, "r");
	int ret = load_instruction_from_stream(file);
	fclose(file);
	return ret;
}

int do_eval(void) {
	// TODO: Range check for 'ip' 'dp'.
	size_t ip = 0;
	char* dp = &data[0];
	for (ip = 0; ip < instruction_size; ++ip) {
		switch (instruction[ip]) {
		case '+':
			++(*dp);
			break;
		case '-':
			--(*dp);
			break;
		case '>':
			++dp;
			break;
		case '<':
			--dp;
			break;
		case '.':
			putchar(*dp);
			break;
		case ',': {
			int c = getchar();
			if (c == EOF) {
				return EOF;
			}
			*dp = (char)c;
		}
			break;
		case '[':
			if (*dp == 0) {
				int nest_level = 1;
				do {
					++ip;
					if (ip > instruction_size) {
						fprintf(stderr, "Instruction pointer overrun\n");
						abort();
					}
					switch (instruction[ip]) {
					case '[':
						++nest_level;
						break;
					case ']':
						--nest_level;
						break;
					}
				} while (nest_level > 0);
			}
			break;
		case ']':
			if (*dp != 0) {
				int nest_level = 1;
				do {
					if (ip == 0) {
						fprintf(stderr, "Instruction pointer underrun\n");
						abort();
					}
					--ip;
					switch (instruction[ip]) {
					case ']':
						++nest_level;
						break;
					case '[':
						--nest_level;
						break;
					}
				} while (nest_level > 0);
			}
			break;
		default:
			// nop
			break;
		}
	}
	return 0;
}


int main(int argc, char* argv[]) {
	if (argc < 2) {
		fprintf(stderr, "please specify a file.\n");
		exit(EXIT_FAILURE);
	}

	load_instruction_from_path(argv[1]);

	do_eval();
}