Number of Bytes Free

Task

Implement the function num_bytes_free

• Given a block_header* to the start of the heap, return the number of free bytes left
• Don’t modify the struct definition at the top of the file
• Don’t modify the fake_heaps.h, fake_heaps.o, or Makefile files

Function Signature

// Given a block_header* to the start of the heap, return the number of 
// free bytes left
//
int32_t num_bytes_free(struct block_header* start);

---

Testing

Compiling

• Use the given Makefile to compile your program
  • To use the Makefile just type make into the terminal (Refer back to Week 3 Lab for more information on Makefiles)

Test Cases

• To test your code, you can use the variables heap1, heap2, heap3, heap4, heap5, which are defined in the fake_heaps.h header file.
  • These are pointers to the start of different heaps and have different allocated blocks in each of them
• For example, to use heap1 in testing in your main function, here’s what it could look like

int main() {
    int32_t freeBytes = num_bytes_free(heap1);
 
    printf("Number of free bytes: %d\n", freeBytes);
 
    return 0;
}

Example

Test Case 1

Input: heap1
Output: 0 (look into fake_heaps.h to see a diagram of each heap)

Test Case 2

Input: heap3
Output: 2544

---

Code

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stddef.h>
#include "fake_heaps.h"
 
struct block_header {
    size_t size_status;
};
 
int32_t num_bytes_free(struct block_header* start){
    int32_t count = 0;
    struct block_header* current = start;
    while(current->size_status != 1){
        uint64_t size = current->size_status & (-4);
        if(current->size_status % 2 == 0){
            count += size;
        }
        void* next = (void*)current + size;
        current = (struct block_header*) next;
    }
    return count;
}