單片機(不基於os)下如何實現簡單的內存管理(malloc,realloc和free函數的重新實現)

實現的原理是將內存分成小的片段進行管理，代碼如下：

#define MEM_BLOCK_SIZE 4096 #define MEM_LARGE_BLOCK_THRESHOLD 40960 //>MEM_LARGE_BLOCK_THRESHOLD :requested size is large block #define MEM_BASE_ADDRESS (0x90000000) #define MEM_ALLOC_TABLE_FIRST_ENTRY 0 #define MAX_MEM_SIZE 7*1024*1024 #define MEM_ALLOC_TABLE_SIZE (MAX_MEM_SIZE/MEM_BLOCK_SIZE) static INT16 memory_map[MEM_ALLOC_TABLE_SIZE]; static char isMemoryManagementReady=0; void *memset(void *s, int c, size_t count) { char *xs = s; while (count--) *xs++ = c; return s; } INT32 ssd_mem_init(void) { memset(memory_map, 0, sizeof(memory_map)); isMemoryManagementReady=1; } INT16 ssd_mem_percentage_used() { int used=0; int i; for(i=0;i<MEM_ALLOC_TABLE_SIZE;i++) { if(memory_map[i]) { used++; } } return used*100/MEM_ALLOC_TABLE_SIZE; } //return -1:FAIL //>=0: return allocated address offset INT32 ssd_mem_malloc(UINT32 size) { int offset=0; int startEntry=MEM_ALLOC_TABLE_FIRST_ENTRY; int nmemb; int i; if(!isMemoryManagementReady) { ssd_mem_init(); } if(size==0) { return -1; } nmemb=size/MEM_BLOCK_SIZE; if(size%MEM_BLOCK_SIZE) { nmemb++; } if(size > MEM_LARGE_BLOCK_THRESHOLD) { for(offset=startEntry;offset<MEM_ALLOC_TABLE_SIZE-nmemb;offset++) { if(!memory_map[offset]) { int vacantSize=0; for(vacantSize=0;vacantSize<nmemb && !memory_map[offset+vacantSize];vacantSize++); if(vacantSize==nmemb) { for(i=0;i<nmemb;i++) { memory_map[offset+i]=nmemb; } return (offset*MEM_BLOCK_SIZE); } } } } else { for(offset=MEM_ALLOC_TABLE_SIZE-1;offset>=0;offset--) { if(!memory_map[offset] && ((offset+nmemb)<=MEM_ALLOC_TABLE_SIZE))//search start of vacant block { int vacantSize=0; for(vacantSize=0;vacantSize<nmemb && !memory_map[offset+vacantSize];vacantSize++); if(vacantSize==nmemb) { for(i=0;i<nmemb;i++) { memory_map[offset+i]=nmemb; } return (offset*MEM_BLOCK_SIZE); } } } } puts("malloc size erorr="); putInt32(size); return -1; } //return 0:OK //return 1:Out of bound INT32 ssd_mem_free(INT32 offset) { int i; if(!isMemoryManagementReady) { ssd_mem_init(); return 1; } if(offset<MAX_MEM_SIZE) { int index=offset/MEM_BLOCK_SIZE; int nmemb=memory_map[index]; for(i=0;i<nmemb;i++) { memory_map[index+i]=0; } return 0; } else { return 1;//out of bound } } void free(void *ptr) { if(ptr==NULL) return; INT32 offset; offset=ptr-MEM_BASE_ADDRESS; ssd_mem_free(offset); } void * malloc(UINT32 size) { INT32 offset; offset=ssd_mem_malloc(size); if(offset==-1) { return NULL; } else return MEM_BASE_ADDRESS+offset; } void *realloc(void *ptr,UINT32 size) { INT32 offset; offset=ssd_mem_malloc(size); if(offset==-1) { puts("realloc error/n"); return NULL; } else { memcpy((void*)(MEM_BASE_ADDRESS+offset),ptr,size); free(ptr); return MEM_BASE_ADDRESS+offset; } }