char* MemoryPool::Allocate(size_t bytes){
assert(bytes > 0);
char* result;
if (bytes <= _memory_remain){
result = _alloc_ptr;
_alloc_ptr += bytes;
_memory_remain -= bytes;
}else{
// We waste the remaining space in the current block.
result = AllocateFallback(bytes);
_memory_remain = _block_size - bytes;
_alloc_ptr = result + bytes;
}
return result;
}
char* Arena::AllocateAligned(size_t bytes) {
const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
assert((align & (align-1)) == 0); // Pointer size should be a power of 2
size_t current_mod = reinterpret_cast<uintptr_t>(alloc_ptr_) & (align-1);
size_t slop = (current_mod == 0 ? 0 : align - current_mod);
size_t needed = bytes + slop;
char* result;
if (needed <= alloc_bytes_remaining_) {
result = alloc_ptr_ + slop;
alloc_ptr_ += needed;
alloc_bytes_remaining_ -= needed;
} else {
// AllocateFallback always returned aligned memory
result = AllocateFallback(bytes);
}
assert((reinterpret_cast<uintptr_t>(result) & (align-1)) == 0);
return result;
}
char* MemoryPool::AllocateAligned(size_t bytes){
const int align = (sizeof(void*) > 8) ? sizeof(void*) : 8;
// Pointer size should be a power of 2
assert((align & (align-1)) == 0);
//当align为power of 2时alloc_ptr_除以align的余数实际就是alloc_ptr_ & (align-1)
size_t cur_mod = reinterpret_cast<uintptr_t>(_alloc_ptr) & (align - 1);
size_t slop = (cur_mod == 0 ? 0 : align - cur_mod);
size_t mem_need = bytes + slop;
char *result;
if (mem_need <= _memory_remain){
result = _alloc_ptr + slop;
_alloc_ptr += mem_need;
_memory_remain -= mem_need;
}else{
// We waste the remaining space in the current block.
result = AllocateFallback(bytes);
_memory_remain = _block_size - bytes;
_alloc_ptr = result + bytes;
}
return result;
}
