brainfuck interpreter written in C

brainfuck.c

// Lucas Wolschick (C) 2022
// You should probably not use this as this has not been tested
// Usage: brainfuck [file]
//
// Try it with this code (available at en.wikipedia.org/wiki/Brainfuck, not mine!)
// ++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.

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

typedef struct VM VM;
struct VM {
	size_t iptr;
	size_t dptr;
	uint8_t* data;
};

typedef enum VM_STATUS VM_STATUS;
enum VM_STATUS {
	VM_RUNNING,
	VM_DONE,
};

VM* vm_new(void) {
	VM* vm = malloc(sizeof(VM));
	vm->iptr = 0;
	vm->dptr = 0;
	vm->data = calloc(30*1000, sizeof(uint8_t));
	return vm;
}

VM_STATUS vm_run(VM* vm, size_t src_len, const char* src) {
	if (vm->iptr >= src_len) {
		return VM_DONE;
	} else {
		switch(src[vm->iptr]) {
			case '>':
				if (vm->dptr == 30*1000)
					// silently ignore
					;
				else
					vm->dptr++;
				break;
			case '<':
				if (vm->dptr > 0)
					vm->dptr--;
				break;
			case '+':
				vm->data[vm->dptr]++;
				break;
			case '-':
				vm->data[vm->dptr]--;
				break;
			case '.':
				putc(vm->data[vm->dptr], stdout);
				break;
			case ',':
				vm->data[vm->dptr] = getc(stdin);
				break;
			case '[':
				if (!vm->data[vm->dptr]) {
					// jump to after matching ]
					size_t idx = vm->iptr + 1;
					int counter = 1;
					while (idx < src_len && counter > 0) {
						if (src[idx] == '[') {
							counter++;
						} else if (src[idx] == ']') {
							counter--;
						}
						idx++;
					}
					vm->iptr = idx-1;
				}
				break;
			case ']':
				if (vm->iptr < 1)
					// we can't have ] at the beginning of the src...
					// silently ignore
					break;
			
				if (vm->data[vm->dptr] != 0) {
					int counter = 1;
					size_t idx = vm->iptr-1;
					do {
						if (src[idx] == ']') {
							counter++;
						} else if (src[idx] == '[') {
							counter--;
						}
						idx--;
					} while (idx > 0 && counter > 0);
					vm->iptr = idx+1;
				}
				break;
			// everything else are commentss
		}
		vm->iptr++;
	}
	return VM_RUNNING;
}

char* read_to_string(const char* path, size_t* length) {
	char* source = 0;
	
	// load file
	FILE* src = fopen(path, "rb");
	if (!src) {
		perror("Could not read brainfuck source");
		return source;
	}
	// get file length
	int begin = ftell(src);
	if (begin == -1) {
		perror("Error seeking file");
		goto fail;
	}
	if (fseek(src, 0, SEEK_END) != 0) {
		puts("Error reading file");
		goto fail;
	}
	int len = ftell(src);
	if (len == -1) {
		perror("Error reading file");
		goto fail;
	}
	if (fseek(src, 0, begin) != 0) {
		puts("Error reading file");
		goto fail;
	};
	// allocate and populate string
	source = malloc(len);
	if (!source) {
		puts("Out of memory");
		goto fail;
	}
	int err = fread(source, 1, len, src);
	if (err < len) {
		if (feof(src)) {
			puts("Error: end of file reached");
			goto fail;
		} else if (ferror(src)) {
			perror("Error reading source file");
			goto fail;
		}
	}
	
	fclose(src);
	*length = len;
	return source;
	
	fail:
	fclose(src);
	free(source);
	return source;
}

int main(int argc, char* argv[]) {
	if (argc > 1) {
		size_t length = 0;
		char* source = read_to_string(argv[1], &length);
		if (!source) {
			return EXIT_FAILURE;
		}
		
		VM* vm = vm_new();
		while (vm_run(vm, length, source) == VM_RUNNING) {}
		
		free(source);
		return EXIT_SUCCESS;
	} else {
		puts("Usage: brainfuck <file>");
		return EXIT_FAILURE;
	}
}