内存拷贝函数 memcpy

2018/12/28 18:47
阅读数 155

windows下实现:

void* __cdecl memcpy(void* dst,const void* src,size_t count)
{
    void*ret=dst;
  #if defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)
  {
       extern void RtlMoveMemory(void *,const void *,size_t count);
       RtlMoveMemory(dst,src,count);
  }
  #else /*defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)*/
  /*
  *copy from lower addresses to higher addresses
  */
  while(count--){
      *(char *)dst = *(char *)src;
      dst = (char *)dst+1;
      src = (char *)src+1;
  }
  #endif  /*defined(_M_MRX000)||defined(_M_ALPHA)||defined(_M_PPC)*/
  return (ret);
}

 

liunx下实现的代码:

void *memcpy(void *to, const void *from, size_t n)
{
   //记录拷贝目的位置,为了返回拷贝内容的首地址
void *xto = to; size_t temp, temp1;  
   //判断拷贝的字节数
if (!n) return xto;
   //
if ((long)to & 1) { char *cto = to; const char *cfrom = from; *cto++ = *cfrom++; to = cto; from = cfrom; n--; } if (n > 2 && (long)to & 2) { short *sto = to; const short *sfrom = from; *sto++ = *sfrom++; to = sto; from = sfrom; n -= 2; } temp = n >> 2; if (temp) { long *lto = to; const long *lfrom = from;   #if defined(CONFIG_M68000) || defined(CONFIG_COLDFIRE) for (; temp; temp--) *lto++ = *lfrom++;   #else asm volatile ( " movel %2,%3\n" " andw #7,%3\n" " lsrl #3,%2\n" " negw %3\n" " jmp %%pc@(1f,%3:w:2)\n" "4: movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" " movel %0@+,%1@+\n" "1: dbra %2,4b\n" " clrw %2\n" " subql #1,%2\n" " jpl 4b" : "=a" (lfrom), "=a" (lto), "=d" (temp), "=&d" (temp1) : "0" (lfrom), "1" (lto), "2" (temp));   #endif to = lto; from = lfrom;    }   if (n & 2) { short *sto = to; const short *sfrom = from; *sto++ = *sfrom++; to = sto; from = sfrom;   }    if (n & 1) {    char *cto = to;    const char *cfrom = from;    *cto = *cfrom;    } return xto; }

 

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