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#include "mem.h"
#include <stdlib.h>
#include <string.h>
bool mem_make_(
Memory* mem, Chunk* chunks, void* blocks, size_t num_blocks,
size_t block_size_bytes) {
assert(mem);
assert((chunks && blocks) || (!chunks && !blocks));
assert(num_blocks >= 1);
mem->block_size_bytes = block_size_bytes;
mem->num_blocks = num_blocks;
mem->next_free_chunk = 0;
// Allocate chunks and blocks if necessary and zero them out.
if (!chunks) {
chunks = calloc(num_blocks, sizeof(Chunk));
blocks = calloc(num_blocks, block_size_bytes);
mem->dynamic = true;
if (!chunks || !blocks) {
return false;
}
} else {
memset(blocks, 0, num_blocks * block_size_bytes);
memset(chunks, 0, num_blocks * sizeof(Chunk));
mem->dynamic = false;
}
mem->chunks = chunks;
mem->blocks = blocks;
// Initialize the head as one large free chunk.
Chunk* head = &mem->chunks[0];
head->num_blocks = num_blocks;
return true;
}
void mem_del_(Memory* mem) {
assert(mem);
if (mem->dynamic) {
if (mem->chunks) {
free(mem->chunks);
mem->chunks = 0;
}
if (mem->blocks) {
free(mem->blocks);
mem->blocks = 0;
}
}
}
void mem_clear_(Memory* mem) {
assert(mem);
mem->next_free_chunk = 0;
memset(mem->blocks, 0, mem->num_blocks * mem->block_size_bytes);
memset(mem->chunks, 0, mem->num_blocks * sizeof(Chunk));
// Initialize the head as one large free chunk.
Chunk* head = &mem->chunks[0];
head->num_blocks = mem->num_blocks;
}
void* mem_alloc_(Memory* mem, size_t num_blocks) {
assert(mem);
assert(num_blocks >= 1);
// Search for the first free chunk that can accommodate num_blocks.
const size_t start = mem->next_free_chunk;
size_t chunk_idx = start;
bool found = false;
do {
Chunk* chunk = &mem->chunks[chunk_idx];
if (!chunk->used) {
if (chunk->num_blocks > num_blocks) {
// Carve out a smaller chunk when the found chunk is larger than
// requested.
// [prev] <--> [chunk] <--> [new next] <--> [next]
const size_t new_next_idx = chunk_idx + num_blocks;
Chunk* new_next = &mem->chunks[new_next_idx];
if (chunk->next) {
mem->chunks[chunk->next].prev = new_next_idx;
}
new_next->prev = chunk_idx;
new_next->next = chunk->next;
chunk->next = new_next_idx;
new_next->num_blocks = chunk->num_blocks - num_blocks;
chunk->num_blocks = num_blocks;
chunk->used = true;
found = true;
break;
} else if (chunk->num_blocks == num_blocks) {
chunk->used = true;
found = true;
break;
}
}
chunk_idx = chunk->next; // Last chunk points back to 0, which is always the
// start of some chunk. 'next' and 'prev' are
// always valid pointers.
} while (chunk_idx != start);
if (found) {
mem->next_free_chunk = mem->chunks[chunk_idx].next;
return &mem->blocks[chunk_idx * mem->block_size_bytes];
} else {
return 0; // Large-enough free chunk not found.
}
}
// The given pointer is a pointer to this first block of the chunk.
void mem_free_(Memory* mem, void** chunk_ptr) {
assert(mem);
assert(chunk_ptr);
const size_t chunk_idx =
((uint8_t*)*chunk_ptr - mem->blocks) / mem->block_size_bytes;
assert(chunk_idx < mem->num_blocks);
Chunk* chunk = &mem->chunks[chunk_idx];
// Disallow double-frees.
assert(chunk->used);
// Zero out the chunk so that we don't get stray values the next time it is
// allocated.
memset(&mem->blocks[chunk_idx], 0, chunk->num_blocks * mem->block_size_bytes);
// Free the chunk. If it is contiguous with other free chunks, then merge.
// We only need to look at the chunk's immediate neighbours because no two
// free chunks are left contiguous after merging.
chunk->used = false;
if (chunk->next) {
Chunk* next = &mem->chunks[chunk->next];
if (!next->used) {
// Pre: [chunk] <--> [next] <--> [next next]
// Post: [ chunk + next ] <--> [next next]
chunk->num_blocks += mem->chunks[chunk->next].num_blocks;
chunk->next = next->next;
if (next->next) {
Chunk* next_next = &mem->chunks[next->next];
next_next->prev = chunk_idx;
}
next->prev = next->next = next->num_blocks = 0;
}
}
if (chunk->prev) {
Chunk* prev = &mem->chunks[chunk->prev];
if (!prev->used) {
// Pre: [prev] <--> [chunk] <--> [next]
// Post: [ prev + chunk ] <--> [next]
prev->num_blocks += chunk->num_blocks;
prev->next = chunk->next;
if (chunk->next) {
Chunk* next = &mem->chunks[chunk->next];
next->prev = chunk->prev;
}
chunk->prev = chunk->next = chunk->num_blocks = 0;
}
}
*chunk_ptr = 0;
}
// The handle is the chunk's index. We don't call it an index in the public API
// because from the user's perspective, two chunks allocated back-to-back need
// not be +1 away (the offset depends on how large the first chunk is).
void* mem_get_chunk_(const Memory* mem, size_t chunk_handle) {
assert(mem);
assert(chunk_handle < mem->num_blocks);
assert(mem->chunks[chunk_handle].used);
return &mem->blocks[chunk_handle * mem->block_size_bytes];
}
// The given chunk pointer is a pointer to the blocks array.
size_t mem_get_chunk_handle_(const Memory* mem, const void* chunk) {
assert(mem);
const size_t block_byte_index = (const uint8_t*)chunk - mem->blocks;
assert(block_byte_index % mem->block_size_bytes == 0);
return block_byte_index / mem->block_size_bytes;
}
size_t mem_capacity_(const Memory* mem) {
assert(mem);
return mem->num_blocks * mem->block_size_bytes;
}
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