Why does my program keep getting stuck while running the mandelbrot brainf*** program? - c

Question

I wanted to improve my C skills, so I search some program's ideas.
Someone propose to create a simple Brainf*** interpreter and then a compiler. So here I am.
I created the interpreter and it works as expected, except with the Mandelbrot program:
A mandelbrot set fractal viewer in brainfuck written by Erik Bosman
+++++++++++++[->++>>>+++++>++>+<<<<<<]>>>>>++++++>--->>>>>>>>>>+++++++++++++++[[
>>>>>>>>>]+[<<<<<<<<<]>>>>>>>>>-]+[>>>>>>>>[-]>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>[-]+
<<<<<<<+++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>>>>+>>>>>>>>>>>>>>>>>>>>>>>>>>
>+<<<<<<<<<<<<<<<<<[<<<<<<<<<]>>>[-]+[>>>>>>[>>>>>>>[-]>>]<<<<<<<<<[<<<<<<<<<]>>
>>>>>[-]+<<<<<<++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>>>+<<<<<<+++++++[-[->>>
>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>>>+<<<<<<<<<<<<<<<<[<<<<<<<<<]>>>[[-]>>>>>>[>>>>>
>>[-<<<<<<+>>>>>>]<<<<<<[->>>>>>+<<+<<<+<]>>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>
[>>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<[->>>>>>>+<<+<<<+<<]>>>>>>>>]<<<<<<<<<[<<<<<<<
<<]>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<[->>>>>>>+<<+<<<<<]>>>>>>>>>+++++++++++++++[[
>>>>>>>>>]+>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>-]+[
>+>>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>[>->>>>[-<<<<+>>>>]<<<<[->>>>+<<<<<[->>[
-<<+>>]<<[->>+>>+<<<<]+>>>>>>>>>]<<<<<<<<[<<<<<<<<<]]>>>>>>>>>[>>>>>>>>>]<<<<<<<
<<[>[->>>>>>>>>+<<<<<<<<<]<<<<<<<<<<]>[->>>>>>>>>+<<<<<<<<<]<+>>>>>>>>]<<<<<<<<<
[>[-]<->>>>[-<<<<+>[<->-<<<<<<+>>>>>>]<[->+<]>>>>]<<<[->>>+<<<]<+<<<<<<<<<]>>>>>
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>>>>>>>]<<<<<<<<<[>>[->>>>>>>>>+<<<<<<<<<]<<<<<<<<<<<]>>[->>>>>>>>>+<<<<<<<<<]<<
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>>>>>>>>>>>>>>>>>>>>>>>]>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>+++++++++++++++[[>>>>
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>>]<<[->>+>>+<<<<]+>>>>>>>>>]<<<<<<<<[<<<<<<<<<]]>>>>>>>>>[>>>>>>>>>]<<<<<<<<<[>
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]<->>>>[-<<<<+>[<->-<<<<<<+>>>>>>]<[->+<]>>>>]<<<[->>>+<<<]<+<<<<<<<<<]>>>>>>>>>
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>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>]>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>++++++++
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-]>>>]<<<<<<<<<[<<<<<<<<<]>>>>+>[-<-<<<<+>>>>>]>[-<<<<<<[->>>>>+<++<<<<]>>>>>[-<
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[>>>>>>>>>]+>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]>[-]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>-]+
[>+>>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>[>->>>>[-<<<<+>>>>]<<<<[->>>>+<<<<<[->>
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<<<<[<<<<<<<<<]>>>>>>>>>-]+[>>>[-<<<->>>]+<<<[->>>->[-<<<<+>>>>]<<<<[->>>>+<<<<<
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>>>>>>>]<<<<<<<<]>>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>[-<<<+>>>]<<<[->>>+>>>>>>[>+>>>
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>>>>>>]<<<<<<<<+<[>[->+>>[-<<-<<<<<<<<<<+>>>>>>>>>>>[-<+>]>]<[-<-<<<<<<<<<<+>>>>
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>>>>>>>>>>>>>>>>>>>]>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>+++++++++++++++[[>>>>>>>>
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>>>>>>>>>[>>>[-<<<->>>]+<<<[->>>->[-<<<<+>>>>]<<<<[->>>>+<<<<<<<<<<<<<[<<<<<<<<<
]>>>>[-]+>>>>>[>>>>>>>>>]>+<]]+>>>>[-<<<<->>>>]+<<<<[->>>>-<[-<<<+>>>]<<<[->>>+<
<<<<<<<<<<<[<<<<<<<<<]>>>[-]+>>>>>>[>>>>>>>>>]>[-]+<]]+>[-<[>>>>>>>>>]<<<<<<<<]>
>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>->>[-<<<<+>>>>]<<<<[->>>>+<<[-]<<]>>]<<+>>>>[-<<<<
->>>>]+<<<<[->>>>-<<<<<<.>>]>>>>[-<<<<<<<.>>>>>>>]<<<[-]>[-]>[-]>[-]>[-]>[-]>>>[
>[-]>[-]>[-]>[-]>[-]>[-]>>>]<<<<<<<<<[<<<<<<<<<]>>>>>>>>>[>>>>>[-]>>>>]<<<<<<<<<
[<<<<<<<<<]>+++++++++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>+>>>>>>>>>+<<<<<<<<
<<<<<<[<<<<<<<<<]>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<[->>>>>>>+[-]>>[>>>>>>>>>]<<<<<
<<<<[>>>>>>>[-<<<<<<+>>>>>>]<<<<<<[->>>>>>+<<<<<<<[<<<<<<<<<]>>>>>>>[-]+>>>]<<<<
<<<<<<]]>>>>>>>[-<<<<<<<+>>>>>>>]<<<<<<<[->>>>>>>+>>[>+>>>>[-<<<<->>>>]<<<<[->>>
>+<<<<]>>>>>>>>]<<+<<<<<<<[>>>>>[->>+<<]<<<<<<<<<<<<<<]>>>>>>>>>[>>>>>>>>>]<<<<<
<<<<[>[-]<->>>>>>>[-<<<<<<<+>[<->-<<<+>>>]<[->+<]>>>>>>>]<<<<<<[->>>>>>+<<<<<<]<
+<<<<<<<<<]>>>>>>>-<<<<[-]+<<<]+>>>>>>>[-<<<<<<<->>>>>>>]+<<<<<<<[->>>>>>>->>[>>
>>>[->>+<<]>>>>]<<<<<<<<<[>[-]<->>>>>>>[-<<<<<<<+>[<->-<<<+>>>]<[->+<]>>>>>>>]<<
<<<<[->>>>>>+<<<<<<]<+<<<<<<<<<]>+++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>+<<<
<<[<<<<<<<<<]>>>>>>>>>[>>>>>[-<<<<<->>>>>]+<<<<<[->>>>>->>[-<<<<<<<+>>>>>>>]<<<<
<<<[->>>>>>>+<<<<<<<<<<<<<<<<[<<<<<<<<<]>>>>[-]+>>>>>[>>>>>>>>>]>+<]]+>>>>>>>[-<
<<<<<<->>>>>>>]+<<<<<<<[->>>>>>>-<<[-<<<<<+>>>>>]<<<<<[->>>>>+<<<<<<<<<<<<<<[<<<
<<<<<<]>>>[-]+>>>>>>[>>>>>>>>>]>[-]+<]]+>[-<[>>>>>>>>>]<<<<<<<<]>>>>>>>>]<<<<<<<
<<[<<<<<<<<<]>>>>[-]<<<+++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>-<<<<<[<<<<<<<
<<]]>>>]<<<<.>>>>>>>>>>[>>>>>>[-]>>>]<<<<<<<<<[<<<<<<<<<]>++++++++++[-[->>>>>>>>
>+<<<<<<<<<]>>>>>>>>>]>>>>>+>>>>>>>>>+<<<<<<<<<<<<<<<[<<<<<<<<<]>>>>>>>>[-<<<<<<
<<+>>>>>>>>]<<<<<<<<[->>>>>>>>+[-]>[>>>>>>>>>]<<<<<<<<<[>>>>>>>>[-<<<<<<<+>>>>>>
>]<<<<<<<[->>>>>>>+<<<<<<<<[<<<<<<<<<]>>>>>>>>[-]+>>]<<<<<<<<<<]]>>>>>>>>[-<<<<<
<<<+>>>>>>>>]<<<<<<<<[->>>>>>>>+>[>+>>>>>[-<<<<<->>>>>]<<<<<[->>>>>+<<<<<]>>>>>>
>>]<+<<<<<<<<[>>>>>>[->>+<<]<<<<<<<<<<<<<<<]>>>>>>>>>[>>>>>>>>>]<<<<<<<<<[>[-]<-
>>>>>>>>[-<<<<<<<<+>[<->-<<+>>]<[->+<]>>>>>>>>]<<<<<<<[->>>>>>>+<<<<<<<]<+<<<<<<
<<<]>>>>>>>>-<<<<<[-]+<<<]+>>>>>>>>[-<<<<<<<<->>>>>>>>]+<<<<<<<<[->>>>>>>>->[>>>
>>>[->>+<<]>>>]<<<<<<<<<[>[-]<->>>>>>>>[-<<<<<<<<+>[<->-<<+>>]<[->+<]>>>>>>>>]<<
<<<<<[->>>>>>>+<<<<<<<]<+<<<<<<<<<]>+++++[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>>
+>>>>>>>>>>>>>>>>>>>>>>>>>>>+<<<<<<[<<<<<<<<<]>>>>>>>>>[>>>>>>[-<<<<<<->>>>>>]+<
<<<<<[->>>>>>->>[-<<<<<<<<+>>>>>>>>]<<<<<<<<[->>>>>>>>+<<<<<<<<<<<<<<<<<[<<<<<<<
<<]>>>>[-]+>>>>>[>>>>>>>>>]>+<]]+>>>>>>>>[-<<<<<<<<->>>>>>>>]+<<<<<<<<[->>>>>>>>
-<<[-<<<<<<+>>>>>>]<<<<<<[->>>>>>+<<<<<<<<<<<<<<<[<<<<<<<<<]>>>[-]+>>>>>>[>>>>>>
>>>]>[-]+<]]+>[-<[>>>>>>>>>]<<<<<<<<]>>>>>>>>]<<<<<<<<<[<<<<<<<<<]>>>>[-]<<<++++
+[-[->>>>>>>>>+<<<<<<<<<]>>>>>>>>>]>>>>>->>>>>>>>>>>>>>>>>>>>>>>>>>>-<<<<<<[<<<<
<<<<<]]>>>]
I don't understand why, but my program keeps getting stuck in some sort of endless loop. I try to debug it using gdb but it's hard to find the right breakpoint in order to see why it stuck.
The program is as follows:
#include <stdio.h>
#include <stdlib.h>
// Brainfuck instructions
// > Math stuff
#define INCR '+' // +1 on current MS
#define DECR '-' // -1 on current MS
// > Memory slot stuff
#define FORW '>' // Go to next MS
#define BACK '<' // Go to previous MS
// > Logic stuff
#define SJMP '[' // Loop till current MS value is equal to zero
#define EJMP ']' // Jump to the beginning of the loop
// > I/O stuff
#define PRTC '.' // Print character with MS value as ASCII code
#define GETC ',' // Get an user input ASCII character code
typedef unsigned char byte;
// The brainfuck program struct
typedef struct {
byte *values;
int size;
int index;
byte *loops_starts;
int loop_size;
int loop_index;
} BrainfuckProgram;
void initialize(BrainfuckProgram *bfp) {
bfp->values = malloc(bfp->size * sizeof(*bfp->values));
bfp->loops_starts = malloc(bfp->size * sizeof(*bfp->loops_starts));
}
int allocate_values(BrainfuckProgram *bfp) {
byte *newMem = realloc(bfp->values, bfp->size * sizeof(byte));
if (!newMem) {
return 1;
}
bfp->values = newMem;
return 0;
}
int allocate_new_loop(BrainfuckProgram *bfp) {
byte *newMem = realloc(bfp->loops_starts, bfp->loop_size * sizeof(byte));
if (!newMem) {
return 1;
}
bfp->loops_starts = newMem;
return 0;
}
void set_value(BrainfuckProgram *bfp, byte value) {
int tempValue = value < 0 ? 255: value % 256;
*(bfp->values + bfp->index) = tempValue;
}
int get_value(BrainfuckProgram *bfp) {
return *(bfp->values + bfp->index);
}
// FILE functions
int get_file_name(int argc, char *argv[], char** fname) {
if (argc == 1) {
printf("File name is missing\n");
return 1;
}
*fname = argv[1];
return 0;
}
int get_file_size(FILE *file) {
fseek(file, 0L, SEEK_END);
int size = ftell(file);
rewind(file);
return size;
}
// Main function
int main(int argc, char *argv[]) {
// Vector part
BrainfuckProgram bfp = {
.values = NULL,
.size = 1,
.index = 0,
.loops_starts = NULL,
.loop_index = 0,
.loop_size = 0
};
initialize(&bfp);
// FILE Part
char* fname = NULL;
int error = get_file_name(argc, argv, &fname);
if (error) {
goto exit;
}
// Create file variable
FILE *fin = NULL;
fin = fopen(fname, "r");
int size = get_file_size(fin);
// Create a char array of the right size
byte *prog = NULL;
prog = malloc(size * sizeof(*prog));
// Read 1 byte size times
fread(prog, 1, size, fin);
for (int i = 0; i < size; i++) {
byte current = *(prog+i);
switch (current) {
case INCR:
set_value(&bfp, get_value(&bfp) + 1);
break;
case DECR:
set_value(&bfp, get_value(&bfp) - 1);
break;
case FORW:
// if index+1 == size then we are at the
// last element of the vector cause
// size = index - 1
if (bfp.index+1 == bfp.size) {
bfp.size++;
int error = allocate_values(&bfp);
if (error) {
printf("an error occured while forwarding pointer");
goto close;
}
}
bfp.index++;
break;
case BACK:
// bfp.index == 0 then !bfp.index == true
if (!bfp.index) {
printf("can go back from index 0\n");
goto close;
}
bfp.index--;
break;
case SJMP:
if (bfp.loop_index == bfp.size) {
bfp.loop_size++;
int error = allocate_new_loop(&bfp);
if (error) {
printf("an error occured while forwarding pointer");
goto close;
}
}
bfp.loop_index++;
*(bfp.loops_starts + bfp.loop_index) = i;
break;
case EJMP:
if (bfp.loop_index == -1) {
printf("cannot go back");
goto close;
}
if (get_value(&bfp) != 0) {
i = *(bfp.loops_starts + bfp.loop_index);
} else {
bfp.loop_index--;
}
break;
case PRTC:
printf("%c", get_value(&bfp));
break;
case GETC:
; // Semicolon here because of the label error
byte buf;
scanf("%c", &buf);
set_value(&bfp, buf);
break;
}
}
close:
fclose(fin);
exit:
;
return 0;
}
I'd like to have some C related advice on what I have done wrong too.

Answer 1

The Mandelbrot program takes a decent time to run on a good interpreter. Yours, well, it isn't that good. That's why it "hangs" at the start.
Some good ideas that you had, performance-wise:
precalculating loops
Some bad ideas, performance-wise:
Using abstracted allocation functions instead of calling realloc
using scanf and printf instead of getchar and putchar
Some odd things that you did:
Manually truncating an unsigned char when wraparound is implicit
checking if an unsigned char is less than 0
using *(x + y) syntax instead of array indexing x[y]
I don't think you actually use those precalculated loops, if you do then probably not correctly
You also probably create a new precalculated loop every time you go over the loop again
Using the get_value and set_value functions instead of pointers (this will be a performance issue if you don't compile with optimizations)
A couple suggestions:
Try to avoid calling functions when you don't need to as much as possible.
Write a BrainFuck->C compiler using this reference.
On second thought, maybe you should try to debug this program instead.
You may also use my interpreter as a reference if you're OK with GPLv3. Note that it doesn't precalculate loops.