#include <iostream>

using std::cout;

using std::endl;

/*

memcpy说明：

其中要考虑的是

1. 判断输入人指针是否为空

2. 内存是否有重叠

3. 不同架构上是否可以考虑一次拷贝多个进行copy加速，

如在32bit机器上可以每次cpy 4个bytes， 64bit的机器上可以考虑一次cpy8个字节

4. check memcpy 和memmove两个函数的实现

*/

void* memcpy(void* src, void* dst, size_t len)

{

//判断输入人指针是否为空

if(src == NULL||dst == NULL) return NULL;

void * ret = dst;

//内存是否有重叠

if(dst <= src || (char*)dst >= (char*)src + len)

{

for(size_t i= 0; i < len - 4; len -= 4)

{

*(int*)dst = *(int*)src;

dst = (int*)dst + 1;

src = (int*)src + 1;

}

while(len--) {

*(char*)dst = *(char*)src;

dst = (char*)dst + 1;

src = (char*)src + 1;

};

}

else

{

src = (char*)src + len -1;

dst = (char*)dst + len -1;

for(size_t i= 0; i < len - 4; len -= 4)

{

*(int*)dst = *(int*)src;

dst = (int*)dst - 1;

src = (int*)src - 1;

}

while(len--)

{

*(char*)dst= *(char*)src;

dst = (char*)dst - 1;

src = (char*)src - 1;

}

}

return ret;

}

int main(int argc, char const *argv[])

{

char a[] = {'a', 'b','c','d','e','f','g','h','i','j','k'};

char *b = new char[8];

b = (char*)memcpy(a, b, 8);

for(int i = 0; i < 8; ++i)

{

std::cout << b[i]<< " ";

}

return 0;

}