esp-idf/components/heap/heap_tlsf.c

/*
** Two Level Segregated Fit memory allocator, version 3.1.
** Written by Matthew Conte
**	http://tlsf.baisoku.org
**
** Based on the original documentation by Miguel Masmano:
**	http://www.gii.upv.es/tlsf/main/docs
**
** This implementation was written to the specification
** of the document, therefore no GPL restrictions apply.
**
** Copyright (c) 2006-2016, Matthew Conte
** All rights reserved.
**
** Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are met:
**     * Redistributions of source code must retain the above copyright
**       notice, this list of conditions and the following disclaimer.
**     * Redistributions in binary form must reproduce the above copyright
**       notice, this list of conditions and the following disclaimer in the
**       documentation and/or other materials provided with the distribution.
**     * Neither the name of the copyright holder nor the
**       names of its contributors may be used to endorse or promote products
**       derived from this software without specific prior written permission.
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
** ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
** WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
** DISCLAIMED. IN NO EVENT SHALL MATTHEW CONTE BE LIABLE FOR ANY
** DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
** (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
** ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
** SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "multi_heap_config.h"
#include "multi_heap.h"
#include "multi_heap_internal.h"
#include "heap_tlsf.h"

/*
** Architecture-specific bit manipulation routines.
**
** TLSF achieves O(1) cost for malloc and free operations by limiting
** the search for a free block to a free list of guaranteed size
** adequate to fulfill the request, combined with efficient free list
** queries using bitmasks and architecture-specific bit-manipulation
** routines.
**
** Most modern processors provide instructions to count leading zeroes
** in a word, find the lowest and highest set bit, etc. These
** specific implementations will be used when available, falling back
** to a reasonably efficient generic implementation.
**
** NOTE: TLSF spec relies on ffs/fls returning value 0..31.
** ffs/fls return 1-32 by default, returning 0 for error.
*/
static inline __attribute__((__always_inline__)) int tlsf_ffs(unsigned int word)
{
	const unsigned int reverse = word & (~word + 1);
	const int bit = 32 - __builtin_clz(reverse);
	return bit - 1;
}

static inline __attribute__((__always_inline__)) int tlsf_fls(unsigned int word)
{
	const int bit = word ? 32 - __builtin_clz(word) : 0;
	return bit - 1;
}

/*
** Set assert macro, if it has not been provided by the user.
*/
#if !defined (tlsf_assert)
#define tlsf_assert assert
#endif

/*
** Static assertion mechanism.
*/
#define _tlsf_glue2(x, y) x ## y
#define _tlsf_glue(x, y) _tlsf_glue2(x, y)
#define tlsf_static_assert(exp) \
	typedef char _tlsf_glue(static_assert, __LINE__) [(exp) ? 1 : -1]

/* This code has been tested on 32- and 64-bit (LP/LLP) architectures. */
tlsf_static_assert(sizeof(int) * CHAR_BIT == 32);
tlsf_static_assert(sizeof(size_t) * CHAR_BIT >= 32);
tlsf_static_assert(sizeof(size_t) * CHAR_BIT <= 64);

/* SL_INDEX_COUNT must be <= number of bits in sl_bitmap's storage type. */
tlsf_static_assert(sizeof(unsigned int) * CHAR_BIT >= SL_INDEX_COUNT);

/* Ensure we've properly tuned our sizes. */
tlsf_static_assert(ALIGN_SIZE == SMALL_BLOCK_SIZE / SL_INDEX_COUNT);

static inline __attribute__((__always_inline__)) size_t align_up(size_t x, size_t align)
{
	tlsf_assert(0 == (align & (align - 1)) && "must align to a power of two");
	return (x + (align - 1)) & ~(align - 1);
}

static inline __attribute__((__always_inline__)) size_t align_down(size_t x, size_t align)
{
	tlsf_assert(0 == (align & (align - 1)) && "must align to a power of two");
	return x - (x & (align - 1));
}

static inline __attribute__((__always_inline__)) void* align_ptr(const void* ptr, size_t align)
{
	const tlsfptr_t aligned =
		(tlsf_cast(tlsfptr_t, ptr) + (align - 1)) & ~(align - 1);
	tlsf_assert(0 == (align & (align - 1)) && "must align to a power of two");
	return tlsf_cast(void*, aligned);
}

/*
** Adjust an allocation size to be aligned to word size, and no smaller
** than internal minimum.
*/
static inline __attribute__((__always_inline__)) size_t adjust_request_size(size_t size, size_t align)
{
	size_t adjust = 0;
	if (size)
	{
		const size_t aligned = align_up(size, align);

		/* aligned sized must not exceed block_size_max or we'll go out of bounds on sl_bitmap */
		if (aligned < block_size_max)
		{
			adjust = tlsf_max(aligned, block_size_min);
		}
	}
	return adjust;
}

/*
** TLSF utility functions. In most cases, these are direct translations of
** the documentation found in the white paper.
*/

static inline __attribute__((__always_inline__)) void mapping_insert(size_t size, int* fli, int* sli)
{
	int fl, sl;
	if (size < SMALL_BLOCK_SIZE)
	{
		/* Store small blocks in first list. */
		fl = 0;
		sl = tlsf_cast(int, size) >> 2;
	}
	else
	{
		fl = tlsf_fls(size);
		sl = tlsf_cast(int, size >> (fl - SL_INDEX_COUNT_LOG2)) ^ (1 << SL_INDEX_COUNT_LOG2);
		fl -= (FL_INDEX_SHIFT - 1);
	}
	*fli = fl;
	*sli = sl;
}

/* This version rounds up to the next block size (for allocations) */
static inline __attribute__((__always_inline__)) void mapping_search(size_t size, int* fli, int* sli)
{
	if (size >= SMALL_BLOCK_SIZE)
	{
		const size_t round = (1 << (tlsf_fls(size) - SL_INDEX_COUNT_LOG2)) - 1;
		size += round;
	}
	mapping_insert(size, fli, sli);
}

static inline __attribute__((__always_inline__)) block_header_t* search_suitable_block(control_t* control, int* fli, int* sli)
{
	int fl = *fli;
	int sl = *sli;

	/*
	** First, search for a block in the list associated with the given
	** fl/sl index.
	*/
	unsigned int sl_map = control->sl_bitmap[fl] & (~0U << sl);
	if (!sl_map)
	{
		/* No block exists. Search in the next largest first-level list. */
		const unsigned int fl_map = control->fl_bitmap & (~0U << (fl + 1));
		if (!fl_map)
		{
			/* No free blocks available, memory has been exhausted. */
			return 0;
		}

		fl = tlsf_ffs(fl_map);
		*fli = fl;
		sl_map = control->sl_bitmap[fl];
	}
	tlsf_assert(sl_map && "internal error - second level bitmap is null");
	sl = tlsf_ffs(sl_map);
	*sli = sl;

	/* Return the first block in the free list. */
	return control->blocks[fl][sl];
}

/* Remove a free block from the free list.*/
static inline __attribute__((__always_inline__)) void remove_free_block(control_t* control, block_header_t* block, int fl, int sl)
{
	block_header_t* prev = block->prev_free;
	block_header_t* next = block->next_free;
	tlsf_assert(prev && "prev_free field can not be null");
	tlsf_assert(next && "next_free field can not be null");
	next->prev_free = prev;
	prev->next_free = next;

	/* If this block is the head of the free list, set new head. */
	if (control->blocks[fl][sl] == block)
	{
		control->blocks[fl][sl] = next;

		/* If the new head is null, clear the bitmap. */
		if (next == &control->block_null)
		{
			control->sl_bitmap[fl] &= ~(1 << sl);

			/* If the second bitmap is now empty, clear the fl bitmap. */
			if (!control->sl_bitmap[fl])
			{
				control->fl_bitmap &= ~(1 << fl);
			}
		}
	}
}

/* Insert a free block into the free block list. */
static inline __attribute__((__always_inline__)) void insert_free_block(control_t* control, block_header_t* block, int fl, int sl)
{
	block_header_t* current = control->blocks[fl][sl];
	tlsf_assert(current && "free list cannot have a null entry");
	tlsf_assert(block && "cannot insert a null entry into the free list");
	block->next_free = current;
	block->prev_free = &control->block_null;
	current->prev_free = block;

	tlsf_assert(block_to_ptr(block) == align_ptr(block_to_ptr(block), ALIGN_SIZE)
		&& "block not aligned properly");
	/*
	** Insert the new block at the head of the list, and mark the first-
	** and second-level bitmaps appropriately.
	*/
	control->blocks[fl][sl] = block;
	control->fl_bitmap |= (1 << fl);
	control->sl_bitmap[fl] |= (1 << sl);
}

/* Remove a given block from the free list. */
static inline __attribute__((__always_inline__)) void block_remove(control_t* control, block_header_t* block)
{
	int fl, sl;
	mapping_insert(block_size(block), &fl, &sl);
	remove_free_block(control, block, fl, sl);
}

/* Insert a given block into the free list. */
static inline __attribute__((__always_inline__)) void block_insert(control_t* control, block_header_t* block)
{
	int fl, sl;
	mapping_insert(block_size(block), &fl, &sl);
	insert_free_block(control, block, fl, sl);
}

static inline __attribute__((__always_inline__)) int block_can_split(block_header_t* block, size_t size)
{
	return block_size(block) >= sizeof(block_header_t) + size;
}

/* Split a block into two, the second of which is free. */
static inline __attribute__((__always_inline__)) block_header_t* block_split(block_header_t* block, size_t size)
{
	/* Calculate the amount of space left in the remaining block. */
	block_header_t* remaining =
		offset_to_block(block_to_ptr(block), size - block_header_overhead);

	const size_t remain_size = block_size(block) - (size + block_header_overhead);

	tlsf_assert(block_to_ptr(remaining) == align_ptr(block_to_ptr(remaining), ALIGN_SIZE)
		&& "remaining block not aligned properly");

	tlsf_assert(block_size(block) == remain_size + size + block_header_overhead);
	block_set_size(remaining, remain_size);
	tlsf_assert(block_size(remaining) >= block_size_min && "block split with invalid size");

	block_set_size(block, size);
	block_mark_as_free(remaining);

	return remaining;
}

/* Absorb a free block's storage into an adjacent previous free block. */
static inline __attribute__((__always_inline__)) block_header_t* block_absorb(block_header_t* prev, block_header_t* block)
{
	tlsf_assert(!block_is_last(prev) && "previous block can't be last");
	/* Note: Leaves flags untouched. */
	prev->size += block_size(block) + block_header_overhead;
	block_link_next(prev);

#ifdef MULTI_HEAP_POISONING_SLOW
        /* next_block header needs to be replaced with a fill pattern */
        multi_heap_internal_poison_fill_region(block, sizeof(block_header_t), true /* free */);
#endif

	return prev;
}

/* Merge a just-freed block with an adjacent previous free block. */
static inline __attribute__((__always_inline__)) block_header_t* block_merge_prev(control_t* control, block_header_t* block)
{
	if (block_is_prev_free(block))
	{
		block_header_t* prev = block_prev(block);
		tlsf_assert(prev && "prev physical block can't be null");
		tlsf_assert(block_is_free(prev) && "prev block is not free though marked as such");
		block_remove(control, prev);
		block = block_absorb(prev, block);
	}

	return block;
}

/* Merge a just-freed block with an adjacent free block. */
static inline __attribute__((__always_inline__)) block_header_t* block_merge_next(control_t* control, block_header_t* block)
{
	block_header_t* next = block_next(block);
	tlsf_assert(next && "next physical block can't be null");

	if (block_is_free(next))
	{
		tlsf_assert(!block_is_last(block) && "previous block can't be last");
		block_remove(control, next);
		block = block_absorb(block, next);
	}

	return block;
}

/* Trim any trailing block space off the end of a block, return to pool. */
static inline __attribute__((__always_inline__)) void block_trim_free(control_t* control, block_header_t* block, size_t size)
{
	tlsf_assert(block_is_free(block) && "block must be free");
	if (block_can_split(block, size))
	{
		block_header_t* remaining_block = block_split(block, size);
		block_link_next(block);
		block_set_prev_free(remaining_block);
		block_insert(control, remaining_block);
	}
}

/* Trim any trailing block space off the end of a used block, return to pool. */
static inline __attribute__((__always_inline__)) void block_trim_used(control_t* control, block_header_t* block, size_t size)
{
	tlsf_assert(!block_is_free(block) && "block must be used");
	if (block_can_split(block, size))
	{
		/* If the next block is free, we must coalesce. */
		block_header_t* remaining_block = block_split(block, size);
		block_set_prev_used(remaining_block);

		remaining_block = block_merge_next(control, remaining_block);
		block_insert(control, remaining_block);
	}
}

static inline __attribute__((__always_inline__)) block_header_t* block_trim_free_leading(control_t* control, block_header_t* block, size_t size)
{
	block_header_t* remaining_block = block;
	if (block_can_split(block, size))
	{
		/* We want the 2nd block. */
		remaining_block = block_split(block, size - block_header_overhead);
		block_set_prev_free(remaining_block);

		block_link_next(block);
		block_insert(control, block);
	}

	return remaining_block;
}

static inline  __attribute__((__always_inline__)) block_header_t* block_locate_free(control_t* control, size_t size)
{
	int fl = 0, sl = 0;
	block_header_t* block = 0;

	if (size)
	{
		mapping_search(size, &fl, &sl);

		/*
		** mapping_search can futz with the size, so for excessively large sizes it can sometimes wind up
		** with indices that are off the end of the block array.
		** So, we protect against that here, since this is the only callsite of mapping_search.
		** Note that we don't need to check sl, since it comes from a modulo operation that guarantees it's always in range.
		*/
		if (fl < FL_INDEX_COUNT)
		{
			block = search_suitable_block(control, &fl, &sl);
		}
	}

	if (block)
	{
		tlsf_assert(block_size(block) >= size);
		remove_free_block(control, block, fl, sl);
	}

	return block;
}

static inline __attribute__((__always_inline__)) void* block_prepare_used(control_t* control, block_header_t* block, size_t size)
{
	void* p = 0;
	if (block)
	{
		tlsf_assert(size && "size must be non-zero");
		block_trim_free(control, block, size);
		block_mark_as_used(block);
		p = block_to_ptr(block);
	}
	return p;
}

/* Clear structure and point all empty lists at the null block. */
static void control_construct(control_t* control)
{
	int i, j;

	control->block_null.next_free = &control->block_null;
	control->block_null.prev_free = &control->block_null;

	control->fl_bitmap = 0;
	for (i = 0; i < FL_INDEX_COUNT; ++i)
	{
		control->sl_bitmap[i] = 0;
		for (j = 0; j < SL_INDEX_COUNT; ++j)
		{
			control->blocks[i][j] = &control->block_null;
		}
	}
}

/*
** Debugging utilities.
*/

typedef struct integrity_t
{
	int prev_status;
	int status;
} integrity_t;

#define tlsf_insist(x) { tlsf_assert(x); if (!(x)) { status--; } }

static void integrity_walker(void* ptr, size_t size, int used, void* user)
{
	block_header_t* block = block_from_ptr(ptr);
	integrity_t* integ = tlsf_cast(integrity_t*, user);
	const int this_prev_status = block_is_prev_free(block) ? 1 : 0;
	const int this_status = block_is_free(block) ? 1 : 0;
	const size_t this_block_size = block_size(block);

	int status = 0;
	(void)used;
	tlsf_insist(integ->prev_status == this_prev_status && "prev status incorrect");
	tlsf_insist(size == this_block_size && "block size incorrect");

	integ->prev_status = this_status;
	integ->status += status;
}

int tlsf_check(tlsf_t tlsf)
{
	int i, j;

	control_t* control = tlsf_cast(control_t*, tlsf);
	int status = 0;

	/* Check that the free lists and bitmaps are accurate. */
	for (i = 0; i < FL_INDEX_COUNT; ++i)
	{
		for (j = 0; j < SL_INDEX_COUNT; ++j)
		{
			const int fl_map = control->fl_bitmap & (1 << i);
			const int sl_list = control->sl_bitmap[i];
			const int sl_map = sl_list & (1 << j);
			const block_header_t* block = control->blocks[i][j];

			/* Check that first- and second-level lists agree. */
			if (!fl_map)
			{
				tlsf_insist(!sl_map && "second-level map must be null");
			}

			if (!sl_map)
			{
				tlsf_insist(block == &control->block_null && "block list must be null");
				continue;
			}

			/* Check that there is at least one free block. */
			tlsf_insist(sl_list && "no free blocks in second-level map");
			tlsf_insist(block != &control->block_null && "block should not be null");

			while (block != &control->block_null)
			{
				int fli, sli;
				tlsf_insist(block_is_free(block) && "block should be free");
				tlsf_insist(!block_is_prev_free(block) && "blocks should have coalesced");
				tlsf_insist(!block_is_free(block_next(block)) && "blocks should have coalesced");
				tlsf_insist(block_is_prev_free(block_next(block)) && "block should be free");
				tlsf_insist(block_size(block) >= block_size_min && "block not minimum size");

				mapping_insert(block_size(block), &fli, &sli);
				tlsf_insist(fli == i && sli == j && "block size indexed in wrong list");
				block = block->next_free;
			}
		}
	}

	return status;
}

#undef tlsf_insist

static void default_walker(void* ptr, size_t size, int used, void* user)
{
	(void)user;
	printf("\t%p %s size: %x (%p)\n", ptr, used ? "used" : "free", (unsigned int)size, block_from_ptr(ptr));
}

void tlsf_walk_pool(pool_t pool, tlsf_walker walker, void* user)
{
	tlsf_walker pool_walker = walker ? walker : default_walker;
	block_header_t* block =
		offset_to_block(pool, -(int)block_header_overhead);

	while (block && !block_is_last(block))
	{
		pool_walker(
			block_to_ptr(block),
			block_size(block),
			!block_is_free(block),
			user);
		block = block_next(block);
	}
}

size_t tlsf_block_size(void* ptr)
{
	size_t size = 0;
	if (ptr)
	{
		const block_header_t* block = block_from_ptr(ptr);
		size = block_size(block);
	}
	return size;
}

int tlsf_check_pool(pool_t pool)
{
	/* Check that the blocks are physically correct. */
	integrity_t integ = { 0, 0 };
	tlsf_walk_pool(pool, integrity_walker, &integ);

	return integ.status;
}

/*
** Size of the TLSF structures in a given memory block passed to
** tlsf_create, equal to the size of a control_t
*/
size_t tlsf_size(void)
{
	return sizeof(control_t);
}

size_t tlsf_align_size(void)
{
	return ALIGN_SIZE;
}

size_t tlsf_block_size_min(void)
{
	return block_size_min;
}

size_t tlsf_block_size_max(void)
{
	return block_size_max;
}

/*
** Overhead of the TLSF structures in a given memory block passed to
** tlsf_add_pool, equal to the overhead of a free block and the
** sentinel block.
*/
size_t tlsf_pool_overhead(void)
{
	return 2 * block_header_overhead;
}

size_t tlsf_alloc_overhead(void)
{
	return block_header_overhead;
}

pool_t tlsf_add_pool(tlsf_t tlsf, void* mem, size_t bytes)
{
	block_header_t* block;
	block_header_t* next;

	const size_t pool_overhead = tlsf_pool_overhead();
	const size_t pool_bytes = align_down(bytes - pool_overhead, ALIGN_SIZE);

	if (((ptrdiff_t)mem % ALIGN_SIZE) != 0)
	{
		printf("tlsf_add_pool: Memory must be aligned by %u bytes.\n",
			(unsigned int)ALIGN_SIZE);
		return 0;
	}

	if (pool_bytes < block_size_min || pool_bytes > block_size_max)
	{
#if defined (TLSF_64BIT)
		printf("tlsf_add_pool: Memory size must be between 0x%x and 0x%x00 bytes.\n",
			(unsigned int)(pool_overhead + block_size_min),
			(unsigned int)((pool_overhead + block_size_max) / 256));
#else
		printf("tlsf_add_pool: Memory size must be between %u and %u bytes.\n",
			(unsigned int)(pool_overhead + block_size_min),
			(unsigned int)(pool_overhead + block_size_max));
#endif
		return 0;
	}

	/*
	** Create the main free block. Offset the start of the block slightly
	** so that the prev_phys_block field falls outside of the pool -
	** it will never be used.
	*/
	block = offset_to_block(mem, -(tlsfptr_t)block_header_overhead);
	block_set_size(block, pool_bytes);
	block_set_free(block);
	block_set_prev_used(block);
	block_insert(tlsf_cast(control_t*, tlsf), block);

	/* Split the block to create a zero-size sentinel block. */
	next = block_link_next(block);
	block_set_size(next, 0);
	block_set_used(next);
	block_set_prev_free(next);

	return mem;
}

void tlsf_remove_pool(tlsf_t tlsf, pool_t pool)
{
	control_t* control = tlsf_cast(control_t*, tlsf);
	block_header_t* block = offset_to_block(pool, -(int)block_header_overhead);

	int fl = 0, sl = 0;

	tlsf_assert(block_is_free(block) && "block should be free");
	tlsf_assert(!block_is_free(block_next(block)) && "next block should not be free");
	tlsf_assert(block_size(block_next(block)) == 0 && "next block size should be zero");

	mapping_insert(block_size(block), &fl, &sl);
	remove_free_block(control, block, fl, sl);
}

/*
** TLSF main interface.
*/


tlsf_t tlsf_create(void* mem)
{
#if _DEBUG
	if (test_ffs_fls())
	{
		return 0;
	}
#endif

	if (((tlsfptr_t)mem % ALIGN_SIZE) != 0)
	{
		printf("tlsf_create: Memory must be aligned to %u bytes.\n",
			(unsigned int)ALIGN_SIZE);
		return 0;
	}

	control_construct(tlsf_cast(control_t*, mem));

	return tlsf_cast(tlsf_t, mem);
}

pool_t tlsf_get_pool(tlsf_t tlsf)
{
	return tlsf_cast(pool_t, (char*)tlsf + tlsf_size());
}

tlsf_t tlsf_create_with_pool(void* mem, size_t bytes)
{
	tlsf_t tlsf = tlsf_create(mem);
	tlsf_add_pool(tlsf, (char*)mem + tlsf_size(), bytes - tlsf_size());
	return tlsf;
}

void* tlsf_malloc(tlsf_t tlsf, size_t size)
{
	control_t* control = tlsf_cast(control_t*, tlsf);
	size_t adjust = adjust_request_size(size, ALIGN_SIZE);
	block_header_t* block = block_locate_free(control, adjust);
	return block_prepare_used(control, block, adjust);
}

void* tlsf_memalign(tlsf_t tlsf, size_t align, size_t size)
{
	control_t* control = tlsf_cast(control_t*, tlsf);
	const size_t adjust = adjust_request_size(size, ALIGN_SIZE);

	/*
	** We must allocate an additional minimum block size bytes so that if
	** our free block will leave an alignment gap which is smaller, we can
	** trim a leading free block and release it back to the pool. We must
	** do this because the previous physical block is in use, therefore
	** the prev_phys_block field is not valid, and we can't simply adjust
	** the size of that block.
	*/
	const size_t gap_minimum = sizeof(block_header_t);
	const size_t size_with_gap = adjust_request_size(adjust + align + gap_minimum, align);

	/*
	** If alignment is less than or equals base alignment, we're done.
	** If we requested 0 bytes, return null, as tlsf_malloc(0) does.
	*/
	const size_t aligned_size = (adjust && align > ALIGN_SIZE) ? size_with_gap : adjust;

	block_header_t* block = block_locate_free(control, aligned_size);

	/* This can't be a static assert. */
	tlsf_assert(sizeof(block_header_t) == block_size_min + block_header_overhead);

	if (block)
	{
		void* ptr = block_to_ptr(block);
		void* aligned = align_ptr(ptr, align);
		size_t gap = tlsf_cast(size_t,
			tlsf_cast(tlsfptr_t, aligned) - tlsf_cast(tlsfptr_t, ptr));

		/* If gap size is too small, offset to next aligned boundary. */
		if (gap && gap < gap_minimum)
		{
			const size_t gap_remain = gap_minimum - gap;
			const size_t offset = tlsf_max(gap_remain, align);
			const void* next_aligned = tlsf_cast(void*,
				tlsf_cast(tlsfptr_t, aligned) + offset);

			aligned = align_ptr(next_aligned, align);
			gap = tlsf_cast(size_t,
				tlsf_cast(tlsfptr_t, aligned) - tlsf_cast(tlsfptr_t, ptr));
		}

		if (gap)
		{
			tlsf_assert(gap >= gap_minimum && "gap size too small");
			block = block_trim_free_leading(control, block, gap);
		}
	}

	return block_prepare_used(control, block, adjust);
}

void tlsf_free(tlsf_t tlsf, void* ptr)
{
	/* Don't attempt to free a NULL pointer. */
	if (ptr)
	{
		control_t* control = tlsf_cast(control_t*, tlsf);
		block_header_t* block = block_from_ptr(ptr);
		tlsf_assert(!block_is_free(block) && "block already marked as free");
		block_mark_as_free(block);
		block = block_merge_prev(control, block);
		block = block_merge_next(control, block);
		block_insert(control, block);
	}
}

/*
** The TLSF block information provides us with enough information to
** provide a reasonably intelligent implementation of realloc, growing or
** shrinking the currently allocated block as required.
**
** This routine handles the somewhat esoteric edge cases of realloc:
** - a non-zero size with a null pointer will behave like malloc
** - a zero size with a non-null pointer will behave like free
** - a request that cannot be satisfied will leave the original buffer
**   untouched
** - an extended buffer size will leave the newly-allocated area with
**   contents undefined
*/
void* tlsf_realloc(tlsf_t tlsf, void* ptr, size_t size)
{
	control_t* control = tlsf_cast(control_t*, tlsf);
	void* p = 0;

	/* Zero-size requests are treated as free. */
	if (ptr && size == 0)
	{
		tlsf_free(tlsf, ptr);
	}
	/* Requests with NULL pointers are treated as malloc. */
	else if (!ptr)
	{
		p = tlsf_malloc(tlsf, size);
	}
	else
	{
		block_header_t* block = block_from_ptr(ptr);
		block_header_t* next = block_next(block);

		const size_t cursize = block_size(block);
		const size_t combined = cursize + block_size(next) + block_header_overhead;
		const size_t adjust = adjust_request_size(size, ALIGN_SIZE);

		tlsf_assert(!block_is_free(block) && "block already marked as free");

		/*
		** If the next block is used, or when combined with the current
		** block, does not offer enough space, we must reallocate and copy.
		*/
		if (adjust > cursize && (!block_is_free(next) || adjust > combined))
		{
			p = tlsf_malloc(tlsf, size);
			if (p)
			{
				const size_t minsize = tlsf_min(cursize, size);
				memcpy(p, ptr, minsize);
				tlsf_free(tlsf, ptr);
			}
		}
		else
		{
			/* Do we need to expand to the next block? */
			if (adjust > cursize)
			{
				block_merge_next(control, block);
				block_mark_as_used(block);
			}

			/* Trim the resulting block and return the original pointer. */
			block_trim_used(control, block, adjust);
			p = ptr;
		}
	}

	return p;
}