123 lines
3.2 KiB
C
123 lines
3.2 KiB
C
#include "freelist.h"
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#include "stddef.h"
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#include <assert.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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struct __attribute__((packed)) FreeListBlock {
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struct FreeListBlock *next;
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};
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/* Align to nearest multiple of align */
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static inline size_t align_up_to(size_t n, size_t align) {
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return (n + align - 1) & ~(align - 1);
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}
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/* Initialize the FreeList */
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int fl_init(FreeList *fl, uintptr_t start, size_t size_bytes, size_t itemsize) {
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/* Fiddle around according to your need, (void *) alignment seems to be enough,
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* but MAX_ALIGN_T is also an option. Especially for allocator implementation. */
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size_t size = align_up_to(itemsize, sizeof(void *));
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if (size < sizeof(FreeListBlock) || !fl) {
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return 0;
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}
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fl->start = start;
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fl->end = start + size_bytes;
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fl->size = size;
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fl->allocated = 0;
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FreeListBlock *block = (FreeListBlock *)start;
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for (size_t i = 0; i < fl_capacity(fl); i++) {
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block->next = (FreeListBlock *)((void *)block + size);
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block = block->next;
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}
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block->next = NULL; /* Last block */
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fl->free = (FreeListBlock *)start;
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return 1;
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}
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/* Allocate some memory from the FreeList */
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void *fl_alloc(FreeList *fl) {
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if (!fl->free)
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return NULL;
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FreeListBlock *m = fl->free;
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fl->free = fl->free->next; /* May be null, which is fine */
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fl->allocated++;
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memset((void *)m, 0, sizeof(FreeListBlock));
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return ((void *)m);
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}
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/* Return some memory to the FreeList */
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int fl_free(FreeList *fl, void *ptr) {
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if (!fl_is_managed(fl, ptr))
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return 0; /* We cant free memory we do not own */
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FreeListBlock *block = (FreeListBlock *)ptr;
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block->next = fl->free; /* May be null, which is fine */
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fl->free = block;
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fl->allocated--;
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return 1;
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}
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/* Returns how many slots are occupied */
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size_t fl_allocated(FreeList *fl) {
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return fl->allocated;
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}
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/* Returns how many free slots are available (O(1)) */
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size_t fl_available(FreeList *fl) {
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return fl_capacity(fl) - fl->allocated;
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}
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/* Returns the total amount of items the freelist will hold */
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size_t fl_capacity(FreeList *fl) {
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return (fl->end - fl->start) / fl->size;
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}
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/* Check if a piece of memory is managed by the FreeList */
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int fl_is_managed(FreeList *fl, void *ptr) {
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uintptr_t p = (uintptr_t)ptr;
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if (p < fl->start || p >= fl->end) {
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return 0; // outside pool
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}
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return ((p - fl->start) % fl->size) == 0; // aligned to block
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}
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/* Returns the ratio of metadata versus data as a scalar in range 0..1 */
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float fl_utilization(FreeList *fl, size_t itemsize) {
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return (float)itemsize / fl->size;
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}
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/* Walks the free pages/slots, returns total count (O(n), given no cycles) */
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size_t fl_check(FreeList *fl) {
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int avail = 0;
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FreeListBlock *cursor = fl->free;
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while (cursor->next != NULL) {
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cursor = cursor->next;
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if (!fl_is_managed(fl, cursor)) {
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printf("Unused memory at: %zX\n", (size_t)cursor->next);
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printf("Min memory at: %zX\n", (size_t)fl->start);
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printf("Max memory at: %zX\n", (size_t)fl->end);
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return 0;
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}
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avail++;
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}
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return avail;
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}
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