wip linkedlist

src/jalloc.c

@@ -1,16 +1,15 @@
+#include <assert.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdbool.h>
+#include <stdlib.h>
 
 #define HEAP_SIZE (1024 * 1024 * 2)
 #define ALIGNMENT 16
 #define HEADER_SIZE 32
 #define FOOTER_SIZE 16
 
-static uint8_t heap[HEAP_SIZE];
-static uint8_t *heap_ptr = heap;
-
 struct Header {
     size_t size;
     bool is_free;
@@ -21,38 +20,156 @@ struct Footer {
     struct Header *header;
 };
 
+struct Block {
+    struct Header *header;
+    struct Block *next;
+};
+
+static uint8_t heap[HEAP_SIZE];
+static struct Block *free_stack;
+static bool initialized = false;
+
+
+
+struct Footer *footer(struct Header *hdr) {
+    return (struct Footer *)((uint8_t *)hdr + hdr->size);
+}
+
+struct Block *pop_first_fit(size_t size) {
+    struct Block *head = free_stack;
+    if (head->header->size >= size) {
+        free_stack = head->next; // remove from free stack
+        return head;
+    }
+    while (head != NULL) {
+        struct Block *next = head->next;
+        if (next == NULL) return NULL;
+        if (next->header->size >= size) {
+            head->next = next->next; // remove from free stack
+            return next;
+        }
+        head = next;
+    }
+    return NULL;
+}
+
+struct Block *pop(struct Block *ptr) {
+    struct Block *head = free_stack;
+    if (head == ptr) {
+        free_stack = head->next;
+        return head;
+    }
+    while (head != NULL) {
+        struct Block *next = head->next;
+        if (next == NULL) break; // if next is NULL, deref below will fault
+        if (next == ptr) {
+            head->next = next->next;
+            return next;
+        }
+    }
+    return NULL;
+}
+
+struct Block *push_header(struct Header *hdr) {
+    struct Block *blk = malloc(sizeof(struct Block));
+    blk->header = hdr;
+    blk->next = free_stack;
+    free_stack = blk;
+}
+
+struct Block *pop_header(struct Header *ptr) {
+    return NULL;
+}
+
 size_t next_multiple_of_align(size_t size) {
     return ((size + (ALIGNMENT - 1)) >> 4) << 4;
 }
 
+void initialize() {
+    // initialize the free list to be a single element containing the entire block
+    size_t initial_block_size = HEAP_SIZE - (HEADER_SIZE + FOOTER_SIZE);
+    free_stack = malloc(sizeof(struct Block));
+    // write a header
+    struct Header *hdr = (struct Header *) heap; // first two alignment slots taken by initial header
+    push_header(hdr);
+    free_stack->header->is_free = true;
+    free_stack->header->size = initial_block_size;
+    free_stack->header->next = NULL;
+    free_stack->next = NULL;
+    // write a footer to heap
+    struct Footer *ftr = (struct Footer *) (heap + initial_block_size - ALIGNMENT);
+    ftr->header = hdr;
+    initialized = true;
+}
+
+struct Block *shrink(struct Block *ptr, size_t size) {
+    // given a size, shrink a block down to the appropriate alignment.
+    // if align(size) + ALIGNMENT*3 is equal to current size, just return initial ptr with noop
+    // otherwise, shrink it down so that we have two blocks.
+    // Push the right block to the free stack
+    // Return left block
+    size = next_multiple_of_align(size); // align if not already so
+    struct Header *hdr = ptr->header;
+    size_t other_size = hdr->size-size-(HEADER_SIZE + FOOTER_SIZE);
+    // if we have space for a full alignment, then a single block of 16 bytes can be allocated there
+    if (other_size >= ALIGNMENT) {
+        hdr->size = size; // resize left block
+        // create our footer
+        struct Footer *ftr = footer(hdr);
+        ftr->header = hdr;
+        // create next header
+        struct Header *next_hdr = (struct Header *)((uint8_t *)ftr + FOOTER_SIZE);
+        next_hdr->size = other_size;
+        next_hdr->is_free = true;
+        next_hdr->next = hdr->next;
+        hdr->next = next_hdr;
+        // create next footer
+        struct Footer *next_ftr = footer(next_hdr);
+        next_ftr->header = next_hdr;
+
+        // push new block to stack
+        push_header(next_hdr);
+    }
+    return ptr;
+}
+
 /**
  * Allocate memory via bump allocation
  */
 void *jalloc(size_t size) {
+    if (!initialized) initialize();
 
     // Total size of allocation = HEADER(padded to ALIGNMENT) + size(padded to ALIGNMENT) + FOOTER(padded to ALIGNMENT)
     size_t aligned_size = next_multiple_of_align(size);
-    void *ptr = heap_ptr + HEADER_SIZE;
-    struct Header *hdr = (struct Header *)heap_ptr;
-    struct Footer *ftr = (struct Footer *)(ptr + aligned_size);
-    if ((uint8_t *)ftr + FOOTER_SIZE > (uint8_t *)heap + sizeof(heap)) return NULL;
-    heap_ptr = (void *) ftr + FOOTER_SIZE; // set next ptr
+    struct Block *blk = pop_first_fit(aligned_size);
+    if (blk == NULL) return NULL;
+
+    blk = shrink(blk, aligned_size);
+
+    struct Header *hdr = blk->header;
+    struct Footer *ftr = footer(hdr);
+    uint8_t* heap_ptr = (void *) ftr + FOOTER_SIZE; // set next ptr
     if ((uint8_t *)heap_ptr > (heap + HEAP_SIZE)) heap_ptr = NULL;
     hdr->size = aligned_size;
     hdr->next = (struct Header *)heap_ptr;
     hdr->is_free = false;
     ftr->header = hdr;
-    return ptr;
+    return (void*)hdr + HEADER_SIZE;
 }
 
 void jfree(void *ptr) {
+    printf("freeing\n\n");
     struct Header *hdr = (struct Header *)(ptr-HEADER_SIZE);
     struct Footer *ftr = (struct Footer *)((uint8_t *)hdr+hdr->size);
     hdr->is_free = true;
     if ((uint8_t *)hdr > heap) { // if this is greater, then there ought to be a foot to the left
+        printf("checking coalescing left\n\n");
         struct Footer *prev_ftr = (struct Footer *)((uint8_t *)hdr-FOOTER_SIZE);
         struct Header *prev_hdr = prev_ftr->header;
         if (prev_hdr->is_free) {
+            printf("coalescing left\n\n");
+            pop_header(prev_hdr);
+            printf("header popped\n\n");
             prev_hdr->size += hdr->size + HEADER_SIZE + FOOTER_SIZE;
             prev_hdr->next=hdr->next;
             ftr->header=prev_hdr;
@@ -60,13 +177,24 @@ void jfree(void *ptr) {
         }
     }
     if (hdr->next != NULL) {
+        printf("checking coalescing right\n\n");
         struct Header *next_hdr = hdr->next;
-        struct Footer *next_ftr = (struct Footer *) ((uint8_t *)next_hdr + next_hdr->size);
+        struct Footer *next_ftr = footer(next_hdr);
+        assert(next_ftr != NULL);
+        assert(next_ftr->header != NULL);
         if (next_hdr->is_free) {
+            printf("coalescing right\n\n");
+            pop_header(next_hdr);
+            printf("header popped\n\n");
             hdr->size += next_hdr->size + HEADER_SIZE + FOOTER_SIZE;
             hdr->next = (struct Header *) ((uint8_t*)next_ftr + FOOTER_SIZE);
+            if ((uint8_t *)hdr->next > (heap + HEAP_SIZE)) hdr->next = NULL;
+            printf("set next\n\n");
+            printf("next ftr?: %s\n\n", (uint8_t*)next_ftr);
             next_ftr->header = hdr;
             ftr = next_ftr;
         }
     }
+    printf("pushing free header\n\n");
+    push_header(hdr);
 }