HW 4 Submission

Author: AlonLib

malloc_3.cpp

@@ -0,0 +1,238 @@
+//
+// Created by Alon on 06/06/2019.
+//
+
+#include <unistd.h>
+#include <cstring>
+#include <cstdlib>
+
+#define MAX_SIZE (100000000)
+#define SBRK_ERROR ((void*)(-1))
+#define ALIGNMENT_BYTES (4)
+#define NUM_OF_BYTES_TO_SPLIT (128)
+
+typedef struct allocated_meta_data {
+    size_t requested_size;
+    void *first_byte_in_block;
+    bool is_free;
+    allocated_meta_data *prev;
+    allocated_meta_data *next;
+} Meta_data
+        __attribute__((aligned(ALIGNMENT_BYTES)));
+
+static Meta_data list_head = {0, NULL, false, NULL, NULL};
+// list_head is a dummy node, wil never be freed true
+
+size_t _size_meta_data();
+void free(void *p);
+
+bool align_program_break() {
+    /// Problem 4 fix
+    void *current_prg_brk = sbrk(0);
+    if (current_prg_brk == SBRK_ERROR) return false;
+    int offset = ((long) current_prg_brk % ALIGNMENT_BYTES);
+    if (offset) {
+        return sbrk(offset);
+    }
+    return true;
+}
+
+size_t align_number_upward(size_t size) {
+    /// Problem 4 fix
+    switch (size % 4) {
+        case 0:
+            return 0;
+        case 1:
+            return 3;
+        case 2:
+            return 2;
+        case 3:
+            return 1;
+    }
+    return 0; // shouldn't get here
+}
+
+void *_helper_on_problem_one(Meta_data *node, size_t size) {
+    /// Problem 1 fix
+    //assert(node->requested_size >= size);
+
+    signed long remaining_free_space_temp =
+            node->requested_size - size - _size_meta_data();
+    size_t remaining_free_space = (remaining_free_space_temp >= 0) ?
+                                  remaining_free_space_temp : 0;
+    if (remaining_free_space < NUM_OF_BYTES_TO_SPLIT) {
+        node->is_free = false;
+        return node->first_byte_in_block;
+    }
+
+    // else 128 or more >> split
+    // case making 1 block into 2 blocks:
+    void *new_p = (void *) (((char *) node->first_byte_in_block) + size);
+    Meta_data *new_node = (Meta_data *) new_p;
+    *new_node = (Meta_data) {remaining_free_space, new_node + 1, true, node,
+                             node->next};
+    node->next = new_node;
+    node->is_free = false;
+    node->requested_size = size;
+    if (new_node->next) new_node->next->prev = new_node;
+    new_node->is_free = false; // preparing for free function
+    free(new_node + 1); /// problem 2 fix
+    return node->first_byte_in_block;
+}
+
+void *_helper_on_problem_three(Meta_data *node, size_t size) {
+    /// Problem 3 fix: "Wilderness"
+    //assert(node && !node->next && size);
+
+    void *res = sbrk(size - node->requested_size); // resizing last node
+    if (res == SBRK_ERROR) return NULL;
+    node->requested_size = size;
+    node->is_free = false;
+    return node->first_byte_in_block;
+}
+
+void *malloc(size_t size) {
+    if (!size || size > MAX_SIZE) return NULL;
+    //if (!align_program_break()) return NULL;
+    /// this change canceled on 21.06.2019
+    Meta_data *node = &list_head;
+    size = size + align_number_upward(size); // fix for problem 4
+
+
+    while (node) { // scan the list for freed space
+        if (node->is_free && node->requested_size >= size) {
+            return _helper_on_problem_one(node, size);
+        }
+        if (node->next)
+            node = node->next;
+        else break; // breaks only for last node in the list
+    }
+
+    if (node && node->is_free && !node->next) { //Wilderness
+        return _helper_on_problem_three(node, size);
+    }
+
+    // not enough free space, allocating:
+    void *res = sbrk(_size_meta_data() + size);
+    if (res == SBRK_ERROR) return NULL;
+    // writing the meta-data
+    Meta_data *new_data = (Meta_data *) res;
+    *new_data = (Meta_data) {size, new_data + 1, false, node, NULL};
+    node->next = new_data;
+    return new_data->first_byte_in_block; // returns the start of the data segment
+}
+
+void *calloc(size_t num, size_t size) {
+    if (!size || !num || size * num > MAX_SIZE) return NULL;
+    size = size * num + align_number_upward(size * num); // fix for problem 4
+    void *res = malloc(size);
+    if (!res) return res;
+    return std::memset(res, 0, size);
+}
+
+void free(void *p) {
+    if (!p) return;
+    Meta_data *meta_data = ((Meta_data *) p) - 1;
+    if (meta_data->is_free) return;
+    meta_data->is_free = true;
+
+    /// Problem 2 fix
+    if (meta_data->prev && meta_data->prev->is_free) {
+        Meta_data *old_data = meta_data;
+        meta_data = old_data->prev;
+        meta_data->requested_size = meta_data->requested_size +
+                                    old_data->requested_size +
+                                    _size_meta_data();
+        meta_data->next = old_data->next;
+        if (meta_data->next) meta_data->next->prev = meta_data;
+
+    }
+    if (meta_data->next && meta_data->next->is_free) {
+        Meta_data *old_data = meta_data->next;
+        meta_data->requested_size = meta_data->requested_size +
+                                    old_data->requested_size +
+                                    _size_meta_data();
+        meta_data->next = old_data->next;
+        if (meta_data->next) meta_data->next->prev = meta_data;
+    }
+}
+
+void *realloc(void *oldp, size_t size) {
+    if (!size || size > MAX_SIZE) return NULL;
+    if (!oldp) return malloc(size);
+    size = size + align_number_upward(size); // fix for problem 4
+
+    Meta_data *node = ((Meta_data *) oldp) - 1;
+    if (node->requested_size >= size) {
+        return _helper_on_problem_one(node, size); // splits block if possible
+    }
+    // ELSE: case new_size > old_size:
+
+    if (node->next && node->next->is_free) {
+        // merging with adjacant higher block
+        node->requested_size += _size_meta_data() + node->next->requested_size;
+        node->next = node->next->next;
+        if (node->next) node->next->prev = node;
+        return realloc(oldp, size);
+    }
+
+    if (!node->next) { // "Wildereness"
+        return _helper_on_problem_three(node, size); // enlarge last block
+    }
+
+    void *res = malloc(size);
+    if (!res) return res;
+    res = memcpy(res, oldp, node->requested_size);
+    free(oldp); /// problem 2 fix
+    return res;
+}
+
+size_t _num_free_blocks() {
+    Meta_data *node = list_head.next;
+    size_t free_blocks_counter = 0;
+    while (node) { // scan the list for freed blocks
+        free_blocks_counter += node->is_free;
+        node = node->next;
+    }
+    return free_blocks_counter;
+}
+
+size_t _num_free_bytes() {
+    Meta_data *node = list_head.next;
+    size_t free_bytes_counter = 0;
+    while (node) { // scan the list for freed blocks
+        free_bytes_counter += node->is_free ? node->requested_size : 0;
+        node = node->next;
+    }
+    return free_bytes_counter;
+}
+
+size_t _num_allocated_blocks() {
+    Meta_data *node = list_head.next;
+    size_t allocated_blocks_counter = 0;
+    while (node) { // scan the list for freed blocks
+        allocated_blocks_counter++;
+        node = node->next;
+    }
+    return allocated_blocks_counter;
+}
+
+size_t _num_allocated_bytes() {
+    Meta_data *node = list_head.next;
+    size_t allocated_bytes_counter = 0;
+    while (node) { // scan the list for freed blocks
+        allocated_bytes_counter += node->requested_size;
+        node = node->next;
+    }
+    return allocated_bytes_counter;
+}
+
+size_t _num_meta_data_bytes() {
+    return _num_allocated_blocks() * _size_meta_data();
+}
+
+size_t _size_meta_data() {
+    return sizeof(struct allocated_meta_data);
+}
+
+