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This commit is contained in:
Nils O. Selåsdal
2026-04-21 01:19:07 +02:00
parent a4cae42114
commit a695653e27
1 changed files with 12 additions and 10 deletions
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src/small_allocator.c
+12 -10
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@@ -35,7 +35,7 @@ typedef struct {
uint8_t* base; // backing store uint8_t* base; // backing store
uint32_t size; // total size uint32_t size; // total size
BlockHeader* heap_start; // first block BlockHeader* heap_start; // first block
BlockHeader* next_fit; // next-fit pointer BlockHeader* next_alloc; // start of free block search
} SmallAllocator; } SmallAllocator;
/* --- Header helpers --- */ /* --- Header helpers --- */
@@ -104,7 +104,7 @@ void small_allocator_init(SmallAllocator* a, void* backing_store, uint32_t size)
first->prev = NULL_BLOCK; first->prev = NULL_BLOCK;
a->heap_start = first; a->heap_start = first;
a->next_fit = first; a->next_alloc = first;
} }
static void maybe_split_block(SmallAllocator* a, BlockHeader* block, uint32_t size) static void maybe_split_block(SmallAllocator* a, BlockHeader* block, uint32_t size)
@@ -147,6 +147,7 @@ static void merge_with_next(SmallAllocator* a, BlockHeader* block)
block->next = next->next; block->next = next->next;
BlockHeader* nextnext = block_from_offset(a, next->next); BlockHeader* nextnext = block_from_offset(a, next->next);
if (nextnext) nextnext->prev = bh_offset(a, block); if (nextnext) nextnext->prev = bh_offset(a, block);
// note - caller have to adjust next_alloc on return
} }
void* small_alloc(SmallAllocator* a, uint32_t size) void* small_alloc(SmallAllocator* a, uint32_t size)
@@ -156,7 +157,7 @@ void* small_alloc(SmallAllocator* a, uint32_t size)
} }
size = ALIGN_UP(size); size = ALIGN_UP(size);
BlockHeader* start = a->next_fit ? a->next_fit : a->heap_start; BlockHeader* start = a->next_alloc ? a->next_alloc : a->heap_start;
BlockHeader* curr = start; BlockHeader* curr = start;
do { do {
@@ -164,7 +165,7 @@ void* small_alloc(SmallAllocator* a, uint32_t size)
maybe_split_block(a, curr, size); maybe_split_block(a, curr, size);
block_set_used(curr); block_set_used(curr);
BlockHeader *next = block_from_offset(a, curr->next); BlockHeader *next = block_from_offset(a, curr->next);
a->next_fit = next ? next : a->heap_start;; a->next_alloc = next ? next : a->heap_start;;
return (uint8_t*)curr + sizeof(BlockHeader); return (uint8_t*)curr + sizeof(BlockHeader);
} }
BlockHeader *next = block_from_offset(a, curr->next); BlockHeader *next = block_from_offset(a, curr->next);
@@ -194,9 +195,9 @@ void small_free(SmallAllocator* a, void* ptr)
BlockHeader* prev = block_from_offset(a, block->prev); BlockHeader* prev = block_from_offset(a, block->prev);
if (prev != NULL && block_is_free(prev)) { if (prev != NULL && block_is_free(prev)) {
merge_with_next(a, prev); merge_with_next(a, prev);
a->next_fit = prev; a->next_alloc = prev;
} else { } else {
a->next_fit = block; a->next_alloc = block;
} }
} }
@@ -213,7 +214,7 @@ void debug_alloc(const SmallAllocator* a)
puts("--debug end--"); puts("--debug end--");
} }
[[gnu::aligned(16)]] char buff[1023 * 1023]; [[gnu::aligned(16)]] char buff[1023];
int main(void) int main(void)
{ {
printf("bh size %zu\n", sizeof(BlockHeader)); printf("bh size %zu\n", sizeof(BlockHeader));
@@ -223,15 +224,16 @@ int main(void)
small_allocator_init(&a, buff, sizeof(buff)); small_allocator_init(&a, buff, sizeof(buff));
debug_alloc(&a); debug_alloc(&a);
ptrs[0] = small_alloc(&a, 32); ptrs[0] = small_alloc(&a, 1023-16*2 - 144);
ptrs[1] = small_alloc(&a, 80); ptrs[1] = small_alloc(&a, 80);
ptrs[2] = small_alloc(&a, 32); ptrs[2] = small_alloc(&a, 32);
small_free(&a, ptrs[1]); debug_alloc(&a);
small_free(&a, ptrs[0]);
ptrs[3] = small_alloc(&a, 12); ptrs[3] = small_alloc(&a, 12);
ptrs[4] = small_alloc(&a, 12); ptrs[4] = small_alloc(&a, 12);
debug_alloc(&a); debug_alloc(&a);
small_free(&a, ptrs[0]); small_free(&a, ptrs[1]);
small_free(&a, ptrs[2]); small_free(&a, ptrs[2]);
small_free(&a, ptrs[3]); small_free(&a, ptrs[3]);
small_free(&a, ptrs[4]); small_free(&a, ptrs[4]);