/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2013, 2014 Damien P. George
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include <assert.h>
#include <stdio.h>
#include <string.h>

#include "py/gc.h"
#include "py/runtime.h"

#include "supervisor/shared/safe_mode.h"

#if MICROPY_ENABLE_GC

#if MICROPY_DEBUG_VERBOSE // print debugging info
#define DEBUG_PRINT (1)
#define DEBUG_printf DEBUG_printf
#else // don't print debugging info
#define DEBUG_PRINT (0)
#define DEBUG_printf(...) (void)0
#endif

// Uncomment this if you want to use a debugger to capture state at every allocation and free.
// #define LOG_HEAP_ACTIVITY 1

// make this 1 to dump the heap each time it changes
#define EXTENSIVE_HEAP_PROFILING (0)

// make this 1 to zero out swept memory to more eagerly
// detect untraced object still in use
#define CLEAR_ON_SWEEP (0)

// ATB = allocation table byte
// 0b00 = FREE -- free block
// 0b01 = HEAD -- head of a chain of blocks
// 0b10 = TAIL -- in the tail of a chain of blocks
// 0b11 = MARK -- marked head block

#define AT_FREE (0)
#define AT_HEAD (1)
#define AT_TAIL (2)
#define AT_MARK (3)

#define BLOCKS_PER_ATB (4)

#define BLOCK_SHIFT(block) (2 * ((block) & (BLOCKS_PER_ATB - 1)))
#define ATB_GET_KIND(block) ((MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] >> BLOCK_SHIFT(block)) & 3)
#define ATB_ANY_TO_FREE(block) do { MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] &= (~(AT_MARK << BLOCK_SHIFT(block))); } while (0)
#define ATB_FREE_TO_HEAD(block) do { MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] |= (AT_HEAD << BLOCK_SHIFT(block)); } while (0)
#define ATB_FREE_TO_TAIL(block) do { MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] |= (AT_TAIL << BLOCK_SHIFT(block)); } while (0)
#define ATB_HEAD_TO_MARK(block) do { MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] |= (AT_MARK << BLOCK_SHIFT(block)); } while (0)
#define ATB_MARK_TO_HEAD(block) do { MP_STATE_MEM(gc_alloc_table_start)[(block) / BLOCKS_PER_ATB] &= (~(AT_TAIL << BLOCK_SHIFT(block))); } while (0)

#define BLOCK_FROM_PTR(ptr) (((byte*)(ptr) - MP_STATE_MEM(gc_pool_start)) / BYTES_PER_BLOCK)
#define PTR_FROM_BLOCK(block) (((block) * BYTES_PER_BLOCK + (uintptr_t)MP_STATE_MEM(gc_pool_start)))
#define ATB_FROM_BLOCK(bl) ((bl) / BLOCKS_PER_ATB)

#if MICROPY_ENABLE_FINALISER
// FTB = finaliser table byte
// if set, then the corresponding block may have a finaliser

#define BLOCKS_PER_FTB (8)

#define FTB_GET(block) ((MP_STATE_MEM(gc_finaliser_table_start)[(block) / BLOCKS_PER_FTB] >> ((block) & 7)) & 1)
#define FTB_SET(block) do { MP_STATE_MEM(gc_finaliser_table_start)[(block) / BLOCKS_PER_FTB] |= (1 << ((block) & 7)); } while (0)
#define FTB_CLEAR(block) do { MP_STATE_MEM(gc_finaliser_table_start)[(block) / BLOCKS_PER_FTB] &= (~(1 << ((block) & 7))); } while (0)
#endif

#if MICROPY_PY_THREAD && !MICROPY_PY_THREAD_GIL
#define GC_ENTER() mp_thread_mutex_lock(&MP_STATE_MEM(gc_mutex), 1)
#define GC_EXIT() mp_thread_mutex_unlock(&MP_STATE_MEM(gc_mutex))
#else
#define GC_ENTER()
#define GC_EXIT()
#endif

#ifdef LOG_HEAP_ACTIVITY
volatile uint32_t change_me;
#pragma GCC push_options
#pragma GCC optimize ("O0")
void __attribute__ ((noinline)) gc_log_change(uint32_t start_block, uint32_t length) {
 change_me += start_block;
 change_me += length; // Break on this line.
}
#pragma GCC pop_options
#endif

// TODO waste less memory; currently requires that all entries in alloc_table have a corresponding block in pool
void gc_init(void *start, void *end) {
 // align end pointer on block boundary
 end = (void*)((uintptr_t)end & (~(BYTES_PER_BLOCK - 1)));
 DEBUG_printf("Initializing GC heap: %p..%p = " UINT_FMT " bytes\n", start, end, (byte*)end - (byte*)start);

 // calculate parameters for GC (T=total, A=alloc table, F=finaliser table, P=pool; all in bytes):
 // T = A + F + P
 // F = A * BLOCKS_PER_ATB / BLOCKS_PER_FTB
 // P = A * BLOCKS_PER_ATB * BYTES_PER_BLOCK
 // => T = A * (1 + BLOCKS_PER_ATB / BLOCKS_PER_FTB + BLOCKS_PER_ATB * BYTES_PER_BLOCK)
 size_t total_byte_len = (byte*)end - (byte*)start;
#if MICROPY_ENABLE_FINALISER
 MP_STATE_MEM(gc_alloc_table_byte_len) = total_byte_len * BITS_PER_BYTE / (BITS_PER_BYTE + BITS_PER_BYTE * BLOCKS_PER_ATB / BLOCKS_PER_FTB + BITS_PER_BYTE * BLOCKS_PER_ATB * BYTES_PER_BLOCK);
#else
 MP_STATE_MEM(gc_alloc_table_byte_len) = total_byte_len / (1 + BITS_PER_BYTE / 2 * BYTES_PER_BLOCK);
#endif

 MP_STATE_MEM(gc_alloc_table_start) = (byte*)start;

#if MICROPY_ENABLE_FINALISER
 size_t gc_finaliser_table_byte_len = (MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB + BLOCKS_PER_FTB - 1) / BLOCKS_PER_FTB;
 MP_STATE_MEM(gc_finaliser_table_start) = MP_STATE_MEM(gc_alloc_table_start) + MP_STATE_MEM(gc_alloc_table_byte_len);
#endif

 size_t gc_pool_block_len = MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB;
 MP_STATE_MEM(gc_pool_start) = (byte*)end - gc_pool_block_len * BYTES_PER_BLOCK;
 MP_STATE_MEM(gc_pool_end) = end;

#if MICROPY_ENABLE_FINALISER
 assert(MP_STATE_MEM(gc_pool_start) >= MP_STATE_MEM(gc_finaliser_table_start) + gc_finaliser_table_byte_len);
#endif

 // clear ATBs
 memset(MP_STATE_MEM(gc_alloc_table_start), 0, MP_STATE_MEM(gc_alloc_table_byte_len));

#if MICROPY_ENABLE_FINALISER
 // clear FTBs
 memset(MP_STATE_MEM(gc_finaliser_table_start), 0, gc_finaliser_table_byte_len);
#endif

 // Set first free ATB index to the start of the heap.
 for (size_t i = 0; i < MICROPY_ATB_INDICES; i++) {
 MP_STATE_MEM(gc_first_free_atb_index)[i] = 0;
 }

 // Set last free ATB index to the end of the heap.
 MP_STATE_MEM(gc_last_free_atb_index) = MP_STATE_MEM(gc_alloc_table_byte_len) - 1;

 // Set the lowest long lived ptr to the end of the heap to start. This will be lowered as long
 // lived objects are allocated.
 MP_STATE_MEM(gc_lowest_long_lived_ptr) = (void*) PTR_FROM_BLOCK(MP_STATE_MEM(gc_alloc_table_byte_len * BLOCKS_PER_ATB));

 // unlock the GC
 MP_STATE_MEM(gc_lock_depth) = 0;

 // allow auto collection
 MP_STATE_MEM(gc_auto_collect_enabled) = true;

 #if MICROPY_GC_ALLOC_THRESHOLD
 // by default, maxuint for gc threshold, effectively turning gc-by-threshold off
 MP_STATE_MEM(gc_alloc_threshold) = (size_t)-1;
 MP_STATE_MEM(gc_alloc_amount) = 0;
 #endif

 #if MICROPY_PY_THREAD
 mp_thread_mutex_init(&MP_STATE_MEM(gc_mutex));
 #endif

 MP_STATE_MEM(permanent_pointers) = NULL;

 DEBUG_printf("GC layout:\n");
 DEBUG_printf(" alloc table at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_alloc_table_start), MP_STATE_MEM(gc_alloc_table_byte_len), MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB);
#if MICROPY_ENABLE_FINALISER
 DEBUG_printf(" finaliser table at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_finaliser_table_start), gc_finaliser_table_byte_len, gc_finaliser_table_byte_len * BLOCKS_PER_FTB);
#endif
 DEBUG_printf(" pool at %p, length " UINT_FMT " bytes, " UINT_FMT " blocks\n", MP_STATE_MEM(gc_pool_start), gc_pool_block_len * BYTES_PER_BLOCK, gc_pool_block_len);
}

void gc_deinit(void) {
 // Run any finalizers before we stop using the heap.
 gc_sweep_all();

 MP_STATE_MEM(gc_pool_start) = 0;
}

void gc_lock(void) {
 GC_ENTER();
 MP_STATE_MEM(gc_lock_depth)++;
 GC_EXIT();
}

void gc_unlock(void) {
 GC_ENTER();
 MP_STATE_MEM(gc_lock_depth)--;
 GC_EXIT();
}

bool gc_is_locked(void) {
 return MP_STATE_MEM(gc_lock_depth) != 0;
}

#ifndef TRACE_MARK
#if DEBUG_PRINT
#define TRACE_MARK(block, ptr) DEBUG_printf("gc_mark(%p)\n", ptr)
#else
#define TRACE_MARK(block, ptr)
#endif
#endif

// Take the given block as the topmost block on the stack. Check all it's
// children: mark the unmarked child blocks and put those newly marked
// blocks on the stack. When all children have been checked, pop off the
// topmost block on the stack and repeat with that one.
STATIC void gc_mark_subtree(size_t block) {
 // Start with the block passed in the argument.
 size_t sp = 0;
 for (;;) {
 // work out number of consecutive blocks in the chain starting with this one
 size_t n_blocks = 0;
 do {
 n_blocks += 1;
 } while (ATB_GET_KIND(block + n_blocks) == AT_TAIL);

 // check this block's children
 void **ptrs = (void**)PTR_FROM_BLOCK(block);
 for (size_t i = n_blocks * BYTES_PER_BLOCK / sizeof(void*); i > 0; i--, ptrs++) {
 void *ptr = *ptrs;
 if (VERIFY_PTR(ptr)) {
 // Mark and push this pointer
 size_t childblock = BLOCK_FROM_PTR(ptr);
 if (ATB_GET_KIND(childblock) == AT_HEAD) {
 // an unmarked head, mark it, and push it on gc stack
 TRACE_MARK(childblock, ptr);
 ATB_HEAD_TO_MARK(childblock);
 if (sp < MICROPY_ALLOC_GC_STACK_SIZE) {
 MP_STATE_MEM(gc_stack)[sp++] = childblock;
 } else {
 MP_STATE_MEM(gc_stack_overflow) = 1;
 }
 }
 }
 }

 // Are there any blocks on the stack?
 if (sp == 0) {
 break; // No, stack is empty, we're done.
 }

 // pop the next block off the stack
 block = MP_STATE_MEM(gc_stack)[--sp];
 }
}

STATIC void gc_deal_with_stack_overflow(void) {
 while (MP_STATE_MEM(gc_stack_overflow)) {
 MP_STATE_MEM(gc_stack_overflow) = 0;

 // scan entire memory looking for blocks which have been marked but not their children
 for (size_t block = 0; block < MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB; block++) {
 // trace (again) if mark bit set
 if (ATB_GET_KIND(block) == AT_MARK) {
 gc_mark_subtree(block);
 }
 }
 }
}

STATIC void gc_sweep(void) {
 #if MICROPY_PY_GC_COLLECT_RETVAL
 MP_STATE_MEM(gc_collected) = 0;
 #endif
 // free unmarked heads and their tails
 int free_tail = 0;
 for (size_t block = 0; block < MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB; block++) {
 switch (ATB_GET_KIND(block)) {
 case AT_HEAD:
#if MICROPY_ENABLE_FINALISER
 if (FTB_GET(block)) {
 mp_obj_base_t *obj = (mp_obj_base_t*)PTR_FROM_BLOCK(block);
 if (obj->type != NULL) {
 // if the object has a type then see if it has a __del__ method
 mp_obj_t dest[2];
 mp_load_method_maybe(MP_OBJ_FROM_PTR(obj), MP_QSTR___del__, dest);
 if (dest[0] != MP_OBJ_NULL) {
 // load_method returned a method, execute it in a protected environment
 #if MICROPY_ENABLE_SCHEDULER
 mp_sched_lock();
 #endif
 mp_call_function_1_protected(dest[0], dest[1]);
 #if MICROPY_ENABLE_SCHEDULER
 mp_sched_unlock();
 #endif
 }
 }
 // clear finaliser flag
 FTB_CLEAR(block);
 }
#endif
 free_tail = 1;
 ATB_ANY_TO_FREE(block);
 #if CLEAR_ON_SWEEP
 memset((void*)PTR_FROM_BLOCK(block), 0, BYTES_PER_BLOCK);
 #endif
 DEBUG_printf("gc_sweep(%x)\n", PTR_FROM_BLOCK(block));

 #ifdef LOG_HEAP_ACTIVITY
 gc_log_change(block, 0);
 #endif
 #if MICROPY_PY_GC_COLLECT_RETVAL
 MP_STATE_MEM(gc_collected)++;
 #endif
 break;

 case AT_TAIL:
 if (free_tail) {
 ATB_ANY_TO_FREE(block);
 #if CLEAR_ON_SWEEP
 memset((void*)PTR_FROM_BLOCK(block), 0, BYTES_PER_BLOCK);
 #endif
 }
 break;

 case AT_MARK:
 ATB_MARK_TO_HEAD(block);
 free_tail = 0;
 break;
 }
 }
}

// Mark can handle NULL pointers because it verifies the pointer is within the heap bounds.
STATIC void gc_mark(void* ptr) {
 if (VERIFY_PTR(ptr)) {
 size_t block = BLOCK_FROM_PTR(ptr);
 if (ATB_GET_KIND(block) == AT_HEAD) {
 // An unmarked head: mark it, and mark all its children
 TRACE_MARK(block, ptr);
 ATB_HEAD_TO_MARK(block);
 gc_mark_subtree(block);
 }
 }
}

void gc_collect_start(void) {
 GC_ENTER();
 MP_STATE_MEM(gc_lock_depth)++;
 #if MICROPY_GC_ALLOC_THRESHOLD
 MP_STATE_MEM(gc_alloc_amount) = 0;
 #endif
 MP_STATE_MEM(gc_stack_overflow) = 0;

 // Trace root pointers. This relies on the root pointers being organised
 // correctly in the mp_state_ctx structure. We scan nlr_top, dict_locals,
 // dict_globals, then the root pointer section of mp_state_vm.
 void **ptrs = (void**)(void*)&mp_state_ctx;
 size_t root_start = offsetof(mp_state_ctx_t, thread.dict_locals);
 size_t root_end = offsetof(mp_state_ctx_t, vm.qstr_last_chunk);
 gc_collect_root(ptrs + root_start / sizeof(void*), (root_end - root_start) / sizeof(void*));

 gc_mark(MP_STATE_MEM(permanent_pointers));

 #if MICROPY_ENABLE_PYSTACK
 // Trace root pointers from the Python stack.
 ptrs = (void**)(void*)MP_STATE_THREAD(pystack_start);
 gc_collect_root(ptrs, (MP_STATE_THREAD(pystack_cur) - MP_STATE_THREAD(pystack_start)) / sizeof(void*));
 #endif
}

void gc_collect_ptr(void *ptr) {
 gc_mark(ptr);
}

void gc_collect_root(void **ptrs, size_t len) {
 for (size_t i = 0; i < len; i++) {
 void *ptr = ptrs[i];
 gc_mark(ptr);
 }
}

void gc_collect_end(void) {
 gc_deal_with_stack_overflow();
 gc_sweep();
 for (size_t i = 0; i < MICROPY_ATB_INDICES; i++) {
 MP_STATE_MEM(gc_first_free_atb_index)[i] = 0;
 }
 MP_STATE_MEM(gc_last_free_atb_index) = MP_STATE_MEM(gc_alloc_table_byte_len) - 1;
 MP_STATE_MEM(gc_lock_depth)--;
 GC_EXIT();
}

void gc_sweep_all(void) {
 GC_ENTER();
 MP_STATE_MEM(gc_lock_depth)++;
 MP_STATE_MEM(gc_stack_overflow) = 0;
 gc_collect_end();
}

void gc_info(gc_info_t *info) {
 GC_ENTER();
 info->total = MP_STATE_MEM(gc_pool_end) - MP_STATE_MEM(gc_pool_start);
 info->used = 0;
 info->free = 0;
 info->max_free = 0;
 info->num_1block = 0;
 info->num_2block = 0;
 info->max_block = 0;
 bool finish = false;
 for (size_t block = 0, len = 0, len_free = 0; !finish;) {
 size_t kind = ATB_GET_KIND(block);
 switch (kind) {
 case AT_FREE:
 info->free += 1;
 len_free += 1;
 len = 0;
 break;

 case AT_HEAD:
 info->used += 1;
 len = 1;
 break;

 case AT_TAIL:
 info->used += 1;
 len += 1;
 break;

 case AT_MARK:
 // shouldn't happen
 break;
 }

 block++;
 finish = (block == MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB);
 // Get next block type if possible
 if (!finish) {
 kind = ATB_GET_KIND(block);
 }

 if (finish || kind == AT_FREE || kind == AT_HEAD) {
 if (len == 1) {
 info->num_1block += 1;
 } else if (len == 2) {
 info->num_2block += 1;
 }
 if (len > info->max_block) {
 info->max_block = len;
 }
 if (finish || kind == AT_HEAD) {
 if (len_free > info->max_free) {
 info->max_free = len_free;
 }
 len_free = 0;
 }
 }
 }

 info->used *= BYTES_PER_BLOCK;
 info->free *= BYTES_PER_BLOCK;
 GC_EXIT();
}

bool gc_alloc_possible(void) {
 return MP_STATE_MEM(gc_pool_start) != 0;
}

// We place long lived objects at the end of the heap rather than the start. This reduces
// fragmentation by localizing the heap churn to one portion of memory (the start of the heap.)
void *gc_alloc(size_t n_bytes, bool has_finaliser, bool long_lived) {
 size_t n_blocks = ((n_bytes + BYTES_PER_BLOCK - 1) & (~(BYTES_PER_BLOCK - 1))) / BYTES_PER_BLOCK;
 DEBUG_printf("gc_alloc(" UINT_FMT " bytes -> " UINT_FMT " blocks)\n", n_bytes, n_blocks);

 // check for 0 allocation
 if (n_blocks == 0) {
 return NULL;
 }

 if (MP_STATE_MEM(gc_pool_start) == 0) {
 reset_into_safe_mode(GC_ALLOC_OUTSIDE_VM);
 }

 GC_ENTER();

 // check if GC is locked
 if (MP_STATE_MEM(gc_lock_depth) > 0) {
 GC_EXIT();
 return NULL;
 }

 size_t found_block = 0xffffffff;
 size_t end_block;
 size_t start_block;
 size_t n_free;
 bool collected = !MP_STATE_MEM(gc_auto_collect_enabled);

 #if MICROPY_GC_ALLOC_THRESHOLD
 if (!collected && MP_STATE_MEM(gc_alloc_amount) >= MP_STATE_MEM(gc_alloc_threshold)) {
 GC_EXIT();
 gc_collect();
 collected = 1;
 GC_ENTER();
 }
 #endif

 bool keep_looking = true;

 // When we start searching on the other side of the crossover block we make sure to
 // perform a collect. That way we'll get the closest free block in our section.
 size_t crossover_block = BLOCK_FROM_PTR(MP_STATE_MEM(gc_lowest_long_lived_ptr));
 while (keep_looking) {
 int8_t direction = 1;
 size_t bucket = MIN(n_blocks, MICROPY_ATB_INDICES) - 1;
 size_t first_free = MP_STATE_MEM(gc_first_free_atb_index)[bucket];
 size_t start = first_free;
 if (long_lived) {
 direction = -1;
 start = MP_STATE_MEM(gc_last_free_atb_index);
 }
 n_free = 0;
 // look for a run of n_blocks available blocks
 for (size_t i = start; keep_looking && first_free <= i && i <= MP_STATE_MEM(gc_last_free_atb_index); i += direction) {
 byte a = MP_STATE_MEM(gc_alloc_table_start)[i];
 // Four ATB states are packed into a single byte.
 int j = 0;
 if (direction == -1) {
 j = 3;
 }
 for (; keep_looking && 0 <= j && j <= 3; j += direction) {
 if ((a & (0x3 << (j * 2))) == 0) {
 if (++n_free >= n_blocks) {
 found_block = i * BLOCKS_PER_ATB + j;
 keep_looking = false;
 }
 } else {
 if (!collected) {
 size_t block = i * BLOCKS_PER_ATB + j;
 if ((direction == 1 && block >= crossover_block) ||
 (direction == -1 && block < crossover_block)) {
 keep_looking = false;
 }
 }
 n_free = 0;
 }
 }
 }
 if (n_free >= n_blocks) {
 break;
 }

 GC_EXIT();
 // nothing found!
 if (collected) {
 return NULL;
 }
 DEBUG_printf("gc_alloc(" UINT_FMT "): no free mem, triggering GC\n", n_bytes);
 gc_collect();
 collected = true;
 // Try again since we've hopefully freed up space.
 keep_looking = true;
 GC_ENTER();
 }
 assert(found_block != 0xffffffff);

 // Found free space ending at found_block inclusive.
 // Also, set last free ATB index to block after last block we found, for start of
 // next scan. Also, whenever we free or shrink a block we must check if this index needs
 // adjusting (see gc_realloc and gc_free).
 if (!long_lived) {
 end_block = found_block;
 start_block = found_block - n_free + 1;
 if (n_blocks < MICROPY_ATB_INDICES) {
 size_t next_free_atb = (found_block + n_blocks) / BLOCKS_PER_ATB;
 // Update all atb indices for larger blocks too.
 for (size_t i = n_blocks - 1; i < MICROPY_ATB_INDICES; i++) {
 MP_STATE_MEM(gc_first_free_atb_index)[i] = next_free_atb;
 }
 }
 } else {
 start_block = found_block;
 end_block = found_block + n_free - 1;
 // Always update the bounds of the long lived area because we assume it is contiguous. (It
 // can still be reset by a sweep.)
 MP_STATE_MEM(gc_last_free_atb_index) = (found_block - 1) / BLOCKS_PER_ATB;
 }

 #ifdef LOG_HEAP_ACTIVITY
 gc_log_change(start_block, end_block - start_block + 1);
 #endif

 // mark first block as used head
 ATB_FREE_TO_HEAD(start_block);

 // mark rest of blocks as used tail
 // TODO for a run of many blocks can make this more efficient
 for (size_t bl = start_block + 1; bl <= end_block; bl++) {
 ATB_FREE_TO_TAIL(bl);
 }

 // get pointer to first block
 // we must create this pointer before unlocking the GC so a collection can find it
 void *ret_ptr = (void*)(MP_STATE_MEM(gc_pool_start) + start_block * BYTES_PER_BLOCK);
 DEBUG_printf("gc_alloc(%p)\n", ret_ptr);

 // If the allocation was long live then update the lowest value. Its used to trigger early
 // collects when allocations fail in their respective section. Its also used to ignore calls to
 // gc_make_long_lived where the pointer is already in the long lived section.
 if (long_lived && ret_ptr < MP_STATE_MEM(gc_lowest_long_lived_ptr)) {
 MP_STATE_MEM(gc_lowest_long_lived_ptr) = ret_ptr;
 }

 #if MICROPY_GC_ALLOC_THRESHOLD
 MP_STATE_MEM(gc_alloc_amount) += n_blocks;
 #endif

 GC_EXIT();

 #if MICROPY_GC_CONSERVATIVE_CLEAR
 // be conservative and zero out all the newly allocated blocks
 memset((byte*)ret_ptr, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK);
 #else
 // zero out the additional bytes of the newly allocated blocks
 // This is needed because the blocks may have previously held pointers
 // to the heap and will not be set to something else if the caller
 // doesn't actually use the entire block. As such they will continue
 // to point to the heap and may prevent other blocks from being reclaimed.
 memset((byte*)ret_ptr + n_bytes, 0, (end_block - start_block + 1) * BYTES_PER_BLOCK - n_bytes);
 #endif

 #if MICROPY_ENABLE_FINALISER
 if (has_finaliser) {
 // clear type pointer in case it is never set
 ((mp_obj_base_t*)ret_ptr)->type = NULL;
 // set mp_obj flag only if it has a finaliser
 GC_ENTER();
 FTB_SET(start_block);
 GC_EXIT();
 }
 #else
 (void)has_finaliser;
 #endif

 #if EXTENSIVE_HEAP_PROFILING
 gc_dump_alloc_table();
 #endif

 return ret_ptr;
}

/*
void *gc_alloc(mp_uint_t n_bytes) {
 return _gc_alloc(n_bytes, false);
}

void *gc_alloc_with_finaliser(mp_uint_t n_bytes) {
 return _gc_alloc(n_bytes, true);
}
*/

// force the freeing of a piece of memory
// TODO: freeing here does not call finaliser
void gc_free(void *ptr) {
 GC_ENTER();
 if (MP_STATE_MEM(gc_lock_depth) > 0) {
 // TODO how to deal with this error?
 GC_EXIT();
 return;
 }

 DEBUG_printf("gc_free(%p)\n", ptr);

 if (ptr == NULL) {
 GC_EXIT();
 } else {
 if (MP_STATE_MEM(gc_pool_start) == 0) {
 reset_into_safe_mode(GC_ALLOC_OUTSIDE_VM);
 }
 // get the GC block number corresponding to this pointer
 assert(VERIFY_PTR(ptr));
 size_t start_block = BLOCK_FROM_PTR(ptr);
 assert(ATB_GET_KIND(start_block) == AT_HEAD);

 #if MICROPY_ENABLE_FINALISER
 FTB_CLEAR(start_block);
 #endif

 // free head and all of its tail blocks
 #ifdef LOG_HEAP_ACTIVITY
 gc_log_change(start_block, 0);
 #endif
 size_t block = start_block;
 do {
 ATB_ANY_TO_FREE(block);
 block += 1;
 } while (ATB_GET_KIND(block) == AT_TAIL);

 // Update the first free pointer for our size only. Not much calls gc_free directly so there
 // is decent chance we'll want to allocate this size again. By only updating the specific
 // size we don't risk something smaller fitting in.
 size_t n_blocks = block - start_block;
 size_t bucket = MIN(n_blocks, MICROPY_ATB_INDICES) - 1;
 size_t new_free_atb = start_block / BLOCKS_PER_ATB;
 if (new_free_atb < MP_STATE_MEM(gc_first_free_atb_index)[bucket]) {
 MP_STATE_MEM(gc_first_free_atb_index)[bucket] = new_free_atb;
 }
 // set the last_free pointer to this block if it's earlier in the heap
 if (new_free_atb > MP_STATE_MEM(gc_last_free_atb_index)) {
 MP_STATE_MEM(gc_last_free_atb_index) = new_free_atb;
 }

 GC_EXIT();

 #if EXTENSIVE_HEAP_PROFILING
 gc_dump_alloc_table();
 #endif
 }
}

size_t gc_nbytes(const void *ptr) {
 GC_ENTER();
 if (VERIFY_PTR(ptr)) {
 size_t block = BLOCK_FROM_PTR(ptr);
 if (ATB_GET_KIND(block) == AT_HEAD) {
 // work out number of consecutive blocks in the chain starting with this on
 size_t n_blocks = 0;
 do {
 n_blocks += 1;
 } while (ATB_GET_KIND(block + n_blocks) == AT_TAIL);
 GC_EXIT();
 return n_blocks * BYTES_PER_BLOCK;
 }
 }

 // invalid pointer
 GC_EXIT();
 return 0;
}

bool gc_has_finaliser(const void *ptr) {
#if MICROPY_ENABLE_FINALISER
 GC_ENTER();
 if (VERIFY_PTR(ptr)) {
 bool has_finaliser = FTB_GET(BLOCK_FROM_PTR(ptr));
 GC_EXIT();
 return has_finaliser;
 }

 // invalid pointer
 GC_EXIT();
#else
 (void) ptr;
#endif
 return false;
}

void *gc_make_long_lived(void *old_ptr) {
 // If its already in the long lived section then don't bother moving it.
 if (old_ptr >= MP_STATE_MEM(gc_lowest_long_lived_ptr)) {
 return old_ptr;
 }
 size_t n_bytes = gc_nbytes(old_ptr);
 if (n_bytes == 0) {
 return old_ptr;
 }
 bool has_finaliser = gc_has_finaliser(old_ptr);

 // Try and find a new area in the long lived section to copy the memory to.
 void* new_ptr = gc_alloc(n_bytes, has_finaliser, true);
 if (new_ptr == NULL) {
 return old_ptr;
 } else if (old_ptr > new_ptr) {
 // Return the old pointer if the new one is lower in the heap and free the new space.
 gc_free(new_ptr);
 return old_ptr;
 }
 // We copy everything over and let the garbage collection process delete the old copy. That way
 // we ensure we don't delete memory that has a second reference. (Though if there is we may
 // confuse things when its mutable.)
 memcpy(new_ptr, old_ptr, n_bytes);
 return new_ptr;
}

#if 0
// old, simple realloc that didn't expand memory in place
void *gc_realloc(void *ptr, mp_uint_t n_bytes) {
 mp_uint_t n_existing = gc_nbytes(ptr);
 if (n_bytes <= n_existing) {
 return ptr;
 } else {
 bool has_finaliser;
 if (ptr == NULL) {
 has_finaliser = false;
 } else {
#if MICROPY_ENABLE_FINALISER
 has_finaliser = FTB_GET(BLOCK_FROM_PTR((mp_uint_t)ptr));
#else
 has_finaliser = false;
#endif
 }
 void *ptr2 = gc_alloc(n_bytes, has_finaliser);
 if (ptr2 == NULL) {
 return ptr2;
 }
 memcpy(ptr2, ptr, n_existing);
 gc_free(ptr);
 return ptr2;
 }
}

#else // Alternative gc_realloc impl

void *gc_realloc(void *ptr_in, size_t n_bytes, bool allow_move) {
 // check for pure allocation
 if (ptr_in == NULL) {
 return gc_alloc(n_bytes, false, false);
 }

 // check for pure free
 if (n_bytes == 0) {
 gc_free(ptr_in);
 return NULL;
 }

 void *ptr = ptr_in;

 GC_ENTER();

 if (MP_STATE_MEM(gc_lock_depth) > 0) {
 GC_EXIT();
 return NULL;
 }

 // get the GC block number corresponding to this pointer
 assert(VERIFY_PTR(ptr));
 size_t block = BLOCK_FROM_PTR(ptr);
 assert(ATB_GET_KIND(block) == AT_HEAD);

 // compute number of new blocks that are requested
 size_t new_blocks = (n_bytes + BYTES_PER_BLOCK - 1) / BYTES_PER_BLOCK;

 // Get the total number of consecutive blocks that are already allocated to
 // this chunk of memory, and then count the number of free blocks following
 // it. Stop if we reach the end of the heap, or if we find enough extra
 // free blocks to satisfy the realloc. Note that we need to compute the
 // total size of the existing memory chunk so we can correctly and
 // efficiently shrink it (see below for shrinking code).
 size_t n_free = 0;
 size_t n_blocks = 1; // counting HEAD block
 size_t max_block = MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB;
 for (size_t bl = block + n_blocks; bl < max_block; bl++) {
 byte block_type = ATB_GET_KIND(bl);
 if (block_type == AT_TAIL) {
 n_blocks++;
 continue;
 }
 if (block_type == AT_FREE) {
 n_free++;
 if (n_blocks + n_free >= new_blocks) {
 // stop as soon as we find enough blocks for n_bytes
 break;
 }
 continue;
 }
 break;
 }

 // return original ptr if it already has the requested number of blocks
 if (new_blocks == n_blocks) {
 GC_EXIT();
 return ptr_in;
 }

 // check if we can shrink the allocated area
 if (new_blocks < n_blocks) {
 // free unneeded tail blocks
 for (size_t bl = block + new_blocks, count = n_blocks - new_blocks; count > 0; bl++, count--) {
 ATB_ANY_TO_FREE(bl);
 }

 // set the last_free pointer to end of this block if it's earlier in the heap
 size_t new_free_atb = (block + new_blocks) / BLOCKS_PER_ATB;
 size_t bucket = MIN(n_blocks - new_blocks, MICROPY_ATB_INDICES) - 1;
 if (new_free_atb < MP_STATE_MEM(gc_first_free_atb_index)[bucket]) {
 MP_STATE_MEM(gc_first_free_atb_index)[bucket] = new_free_atb;
 }
 if (new_free_atb > MP_STATE_MEM(gc_last_free_atb_index)) {
 MP_STATE_MEM(gc_last_free_atb_index) = new_free_atb;
 }

 GC_EXIT();

 #if EXTENSIVE_HEAP_PROFILING
 gc_dump_alloc_table();
 #endif

 #ifdef LOG_HEAP_ACTIVITY
 gc_log_change(block, new_blocks);
 #endif

 return ptr_in;
 }

 // check if we can expand in place
 if (new_blocks <= n_blocks + n_free) {
 // mark few more blocks as used tail
 for (size_t bl = block + n_blocks; bl < block + new_blocks; bl++) {
 assert(ATB_GET_KIND(bl) == AT_FREE);
 ATB_FREE_TO_TAIL(bl);
 }

 GC_EXIT();

 #if MICROPY_GC_CONSERVATIVE_CLEAR
 // be conservative and zero out all the newly allocated blocks
 memset((byte*)ptr_in + n_blocks * BYTES_PER_BLOCK, 0, (new_blocks - n_blocks) * BYTES_PER_BLOCK);
 #else
 // zero out the additional bytes of the newly allocated blocks (see comment above in gc_alloc)
 memset((byte*)ptr_in + n_bytes, 0, new_blocks * BYTES_PER_BLOCK - n_bytes);
 #endif

 #if EXTENSIVE_HEAP_PROFILING
 gc_dump_alloc_table();
 #endif

 #ifdef LOG_HEAP_ACTIVITY
 gc_log_change(block, new_blocks);
 #endif

 return ptr_in;
 }

 #if MICROPY_ENABLE_FINALISER
 bool ftb_state = FTB_GET(block);
 #else
 bool ftb_state = false;
 #endif

 GC_EXIT();

 if (!allow_move) {
 // not allowed to move memory block so return failure
 return NULL;
 }

 // can't resize inplace; try to find a new contiguous chain
 void *ptr_out = gc_alloc(n_bytes, ftb_state, false);

 // check that the alloc succeeded
 if (ptr_out == NULL) {
 return NULL;
 }

 DEBUG_printf("gc_realloc(%p -> %p)\n", ptr_in, ptr_out);
 memcpy(ptr_out, ptr_in, n_blocks * BYTES_PER_BLOCK);
 gc_free(ptr_in);
 return ptr_out;
}
#endif // Alternative gc_realloc impl

bool gc_never_free(void *ptr) {
 // Check to make sure the pointer is on the heap in the first place.
 if (gc_nbytes(ptr) == 0) {
 return false;
 }
 // Pointers are stored in a linked list where each block is BYTES_PER_BLOCK long and the first
 // pointer is the next block of pointers.
 void ** current_reference_block = MP_STATE_MEM(permanent_pointers);
 while (current_reference_block != NULL) {
 for (size_t i = 1; i < BYTES_PER_BLOCK / sizeof(void*); i++) {
 if (current_reference_block[i] == NULL) {
 current_reference_block[i] = ptr;
 return true;
 }
 }
 current_reference_block = current_reference_block[0];
 }
 void** next_block = gc_alloc(BYTES_PER_BLOCK, false, true);
 if (next_block == NULL) {
 return false;
 }
 if (MP_STATE_MEM(permanent_pointers) == NULL) {
 MP_STATE_MEM(permanent_pointers) = next_block;
 } else {
 current_reference_block[0] = next_block;
 }
 next_block[1] = ptr;
 return true;
}

void gc_dump_info(void) {
 gc_info_t info;
 gc_info(&info);
 mp_printf(&mp_plat_print, "GC: total: %u, used: %u, free: %u\n",
 (uint)info.total, (uint)info.used, (uint)info.free);
 mp_printf(&mp_plat_print, " No. of 1-blocks: %u, 2-blocks: %u, max blk sz: %u, max free sz: %u\n",
 (uint)info.num_1block, (uint)info.num_2block, (uint)info.max_block, (uint)info.max_free);
}

void gc_dump_alloc_table(void) {
 GC_ENTER();
 static const size_t DUMP_BYTES_PER_LINE = 64;
 #if !EXTENSIVE_HEAP_PROFILING
 // When comparing heap output we don't want to print the starting
 // pointer of the heap because it changes from run to run.
 mp_printf(&mp_plat_print, "GC memory layout; from %p:", MP_STATE_MEM(gc_pool_start));
 #endif
 for (size_t bl = 0; bl < MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB; bl++) {
 if (bl % DUMP_BYTES_PER_LINE == 0) {
 // a new line of blocks
 {
 // check if this line contains only free blocks
 size_t bl2 = bl;
 while (bl2 < MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB && ATB_GET_KIND(bl2) == AT_FREE) {
 bl2++;
 }
 if (bl2 - bl >= 2 * DUMP_BYTES_PER_LINE) {
 // there are at least 2 lines containing only free blocks, so abbreviate their printing
 mp_printf(&mp_plat_print, "\n (%u lines all free)", (uint)(bl2 - bl) / DUMP_BYTES_PER_LINE);
 bl = bl2 & (~(DUMP_BYTES_PER_LINE - 1));
 if (bl >= MP_STATE_MEM(gc_alloc_table_byte_len) * BLOCKS_PER_ATB) {
 // got to end of heap
 break;
 }
 }
 }
 // print header for new line of blocks
 // (the cast to uint32_t is for 16-bit ports)
 //mp_printf(&mp_plat_print, "\n%05x: ", (uint)(PTR_FROM_BLOCK(bl) & (uint32_t)0xfffff));
 mp_printf(&mp_plat_print, "\n%05x: ", (uint)((bl * BYTES_PER_BLOCK) & (uint32_t)0xfffff));
 }
 int c = ' ';
 switch (ATB_GET_KIND(bl)) {
 case AT_FREE: c = '.'; break;
 /* this prints out if the object is reachable from BSS or STACK (for unix only)
 case AT_HEAD: {
 c = 'h';
 void **ptrs = (void**)(void*)&mp_state_ctx;
 mp_uint_t len = offsetof(mp_state_ctx_t, vm.stack_top) / sizeof(mp_uint_t);
 for (mp_uint_t i = 0; i < len; i++) {
 mp_uint_t ptr = (mp_uint_t)ptrs[i];
 if (VERIFY_PTR(ptr) && BLOCK_FROM_PTR(ptr) == bl) {
 c = 'B';
 break;
 }
 }
 if (c == 'h') {
 ptrs = (void**)&c;
 len = ((mp_uint_t)MP_STATE_THREAD(stack_top) - (mp_uint_t)&c) / sizeof(mp_uint_t);
 for (mp_uint_t i = 0; i < len; i++) {
 mp_uint_t ptr = (mp_uint_t)ptrs[i];
 if (VERIFY_PTR(ptr) && BLOCK_FROM_PTR(ptr) == bl) {
 c = 'S';
 break;
 }
 }
 }
 break;
 }
 */
 /* this prints the uPy object type of the head block */
 case AT_HEAD: {
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wcast-align"
 void **ptr = (void**)(MP_STATE_MEM(gc_pool_start) + bl * BYTES_PER_BLOCK);
#pragma GCC diagnostic pop
 if (*ptr == &mp_type_tuple) { c = 'T'; }
 else if (*ptr == &mp_type_list) { c = 'L'; }
 else if (*ptr == &mp_type_dict) { c = 'D'; }
 else if (*ptr == &mp_type_str || *ptr == &mp_type_bytes) { c = 'S'; }
 #if MICROPY_PY_BUILTINS_BYTEARRAY
 else if (*ptr == &mp_type_bytearray) { c = 'A'; }
 #endif
 #if MICROPY_PY_ARRAY
 else if (*ptr == &mp_type_array) { c = 'A'; }
 #endif
 #if MICROPY_PY_BUILTINS_FLOAT
 else if (*ptr == &mp_type_float) { c = 'F'; }
 #endif
 else if (*ptr == &mp_type_fun_bc) { c = 'B'; }
 else if (*ptr == &mp_type_module) { c = 'M'; }
 else {
 c = 'h';
 #if 0
 // This code prints "Q" for qstr-pool data, and "q" for qstr-str
 // data. It can be useful to see how qstrs are being allocated,
 // but is disabled by default because it is very slow.
 for (qstr_pool_t *pool = MP_STATE_VM(last_pool); c == 'h' && pool != NULL; pool = pool->prev) {
 if ((qstr_pool_t*)ptr == pool) {
 c = 'Q';
 break;
 }
 for (const byte **q = pool->qstrs, **q_top = pool->qstrs + pool->len; q < q_top; q++) {
 if ((const byte*)ptr == *q) {
 c = 'q';
 break;
 }
 }
 }
 #endif
 }
 break;
 }
 case AT_TAIL: c = '='; break;
 case AT_MARK: c = 'm'; break;
 }
 mp_printf(&mp_plat_print, "%c", c);
 }
 mp_print_str(&mp_plat_print, "\n");
 GC_EXIT();
}

#if DEBUG_PRINT
void gc_test(void) {
 mp_uint_t len = 500;
 mp_uint_t *heap = malloc(len);
 gc_init(heap, heap + len / sizeof(mp_uint_t));
 void *ptrs[100];
 {
 mp_uint_t **p = gc_alloc(16, false);
 p[0] = gc_alloc(64, false);
 p[1] = gc_alloc(1, false);
 p[2] = gc_alloc(1, false);
 p[3] = gc_alloc(1, false);
 mp_uint_t ***p2 = gc_alloc(16, false);
 p2[0] = p;
 p2[1] = p;
 ptrs[0] = p2;
 }
 for (int i = 0; i < 25; i+=2) {
 mp_uint_t *p = gc_alloc(i, false);
 printf("p=%p\n", p);
 if (i & 3) {
 //ptrs[i] = p;
 }
 }

 printf("Before GC:\n");
 gc_dump_alloc_table();
 printf("Starting GC...\n");
 gc_collect_start();
 gc_collect_root(ptrs, sizeof(ptrs) / sizeof(void*));
 gc_collect_end();
 printf("After GC:\n");
 gc_dump_alloc_table();
}
#endif

#endif // MICROPY_ENABLE_GC