memcpy記憶體拷貝的改進與最佳化

代碼一：

void *memcpy( void *dest, const void *src, size_t count ){ASSERT((dest != NULL)&&(src != NULL));char *temp_dest = (char *)dest;char *temp_src = (char *)src;while(count--)                                  // 不對是否存在重疊地區進行判斷{*temp_dest++ = *temp_src++;}return dest;}

代碼二：

void* memcpy(void* dest, void* source, size_t count) {       void* ret = dest;      if (dest <= source || dest >= (source + count))       {          //Non-Overlapping Buffers         //copy from lower addresses to higher addresses         while (count --)               *dest++ = *source++;     }     else     {        //Overlapping Buffers       //copy from higher addresses to lower addresses       dest += count - 1;       source += count - 1;       while (count--)                *dest-- = *source--;l     }     return ret;   }

代碼三：

void memcpy(void* dest, const void* src, size_t n){    assert((((uintptr_t) dest | (uintptr_t) src | n) & 0x03) == 0);    uint32_t* d = (uint32_t*) dest;    const uint32_t* s = (uint32_t*) src;    n /= sizeof(uint32_t);   if (d < s) {       /* copy forward */        while (n--) {            *d++ = *s++;        }    } else {        /* copy backward */        d += n;        s += n;        while (n--) {            *--d = *--s;        }    }}

ref：http://snake-hand.iteye.com/blog/1522972