单片机(不基于os)下如何实现简单的内存管理(malloc,realloc和free函数的重新实现)

实现的原理是将内存分成小的片段进行管理，代码如下：

#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_ENTRY0#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;}INT16ssd_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 offsetINT32 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 boundINT32 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;}elsereturn 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;}}