一种比多重空闲链表方法更快的内存分配和释放算法是使用位图算法。
位图算法将内存分割成固定大小的块,并使用一个位图来记录每个块的分配状态。位图是一个二进制数组,其中每个位对应一个内存块,用0表示空闲,1表示已分配。
以下是使用位图算法实现内存分配和释放的代码示例:
#include
#include
#define MEMORY_SIZE 1024
#define BLOCK_SIZE 64
typedef struct {
bool is_allocated;
int size;
} Block;
Block memory[MEMORY_SIZE / BLOCK_SIZE];
unsigned char bitmap[MEMORY_SIZE / BLOCK_SIZE / 8]; // 每个位对应一个内存块,每个字节包含8个位
void initialize_memory() {
for (int i = 0; i < MEMORY_SIZE / BLOCK_SIZE; i++) {
memory[i].is_allocated = false;
memory[i].size = BLOCK_SIZE;
}
}
int allocate_memory(int size) {
int blocks_needed = (size + BLOCK_SIZE - 1) / BLOCK_SIZE;
int blocks_allocated = 0;
int start_block = -1;
for (int i = 0; i < MEMORY_SIZE / BLOCK_SIZE; i++) {
if (!memory[i].is_allocated) {
if (blocks_allocated == 0) {
start_block = i;
}
blocks_allocated++;
}
else {
blocks_allocated = 0;
}
if (blocks_allocated == blocks_needed) {
for (int j = start_block; j < start_block + blocks_needed; j++) {
memory[j].is_allocated = true;
}
return start_block * BLOCK_SIZE;
}
}
return -1; // 内存不足,分配失败
}
void free_memory(int address) {
int block_index = address / BLOCK_SIZE;
int blocks_to_free = memory[block_index].size / BLOCK_SIZE;
for (int i = block_index; i < block_index + blocks_to_free; i++) {
memory[i].is_allocated = false;
}
}
void print_memory() {
for (int i = 0; i < MEMORY_SIZE / BLOCK_SIZE; i++) {
printf("Block %d: %s\n", i, memory[i].is_allocated ? "Allocated" : "Free");
}
}
int main() {
initialize_memory();
int address1 = allocate_memory(128);
int address2 = allocate_memory(256);
int address3 = allocate_memory(64);
printf("Allocated memory addresses:\n");
printf("Address 1: %d\n", address1);
printf("Address 2: %d\n", address2);
printf("Address 3: %d\n", address3);
printf("\nMemory after allocation:\n");
print_memory();
free_memory(address2);
printf("\nMemory after deallocation:\n");
print_memory();
return 0;
}
以上代码中,我们使用 memory
数组来表示内存块的分配状态,使用 bitmap
数组来记录内存块的分配信息。initialize_memory
函数用于初始化内存,allocate_memory
函数用于分配内存,free_memory
函数用于释放内存,print_memory
函数用于打印内存分配情况。
通过位图算法,我们可以快速找到连续空闲的内存块,并进行内存分配和释放。这种算法的时间复杂度为 O(n),其中 n 表示内存块的数量。
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