user: 下面的汇编指令对应的C源代码是什么：

```asm
<memcpy>:
  endbr64
  mov    %rdi,%rax
  mov    %rdi,%r8
  mov    %rsi,%rcx
  or     %rsi,%rax
  and    $0x7,%eax
  je     L53
  lea    -0x1(%rdx),%rsi
  test   %rdx,%rdx
  je     L144
  lea    0x1(%rcx),%rdi
  mov    %r8,%rax
  sub    %rdi,%rax
  cmp    $0xe,%rax
  jbe    L236
  cmp    $0x6,%rsi
  jbe    L236
  cmp    $0xe,%rsi
  jbe    L130
  mov    %rdx,%rdi
  xor    %eax,%eax
  and    $0xfffffffffffffff0,%rdi
  nopw   0x0(%rax,%rax,1)
L43:
  movdqu (%rcx,%rax,1),%xmm1
  movups %xmm1,(%r8,%rax,1)
  add    $0x10,%rax
  cmp    %rdi,%rax
  jne    L43
  mov    %rdx,%rax
  and    $0xfffffffffffffff0,%rax
  lea    (%rcx,%rax,1),%r9
  lea    (%r8,%rax,1),%rdi
  sub    %rax,%rsi
  cmp    %rax,%rdx
  je     L144
  sub    %rax,%rdx
  lea    -0x1(%rdx),%r10
  cmp    $0x6,%r10
  jbe    L89
L270:
  mov    (%rcx,%rax,1),%rcx
  mov    %rcx,(%r8,%rax,1)
  mov    %rdx,%rax
  and    $0xfffffffffffffff8,%rax
  add    %rax,%r9
  add    %rax,%rdi
  sub    %rax,%rsi
  cmp    %rdx,%rax
  je     L144
L89:
  movzbl (%r9),%eax
  mov    %al,(%rdi)
  test   %rsi,%rsi
  je     L144
  movzbl 0x1(%r9),%eax
  mov    %al,0x1(%rdi)
  cmp    $0x1,%rsi
  je     L144
  movzbl 0x2(%r9),%eax
  mov    %al,0x2(%rdi)
  cmp    $0x2,%rsi
  je     L144
  movzbl 0x3(%r9),%eax
  mov    %al,0x3(%rdi)
  cmp    $0x3,%rsi
  je     L144
  movzbl 0x4(%r9),%eax
  mov    %al,0x4(%rdi)
  cmp    $0x4,%rsi
  je     L144
  movzbl 0x5(%r9),%eax
  mov    %al,0x5(%rdi)
  cmp    $0x5,%rsi
  je     L144
  movzbl 0x6(%r9),%eax
  mov    %al,0x6(%rdi)
L144:
  mov    %r8,%rax
  ret
  nopl   (%rax)
L53:
  mov    %rdx,%r9
  shr    $0x2,%r9
  lea    -0x1(%r9),%rsi
  je     L100
  lea    0x8(%rcx),%rdi
  cmp    %rdi,%r8
  je     L70
  cmp    $0x2,%rsi
  jbe    L70
  mov    %rdx,%rdi
  xor    %esi,%esi
  shr    $0x3,%rdi
  nopl   (%rax)
L256:
  movdqu (%rcx,%rsi,1),%xmm0
  add    $0x1,%rax
  movups %xmm0,(%r8,%rsi,1)
  add    $0x10,%rsi
  cmp    %rax,%rdi
  jne    L256
  lea    (%rdi,%rdi,1),%rsi
  shl    $0x4,%rdi
  lea    (%rcx,%rdi,1),%rax
  add    %r8,%rdi
  cmp    %rsi,%r9
  je     L100
  mov    (%rax),%rax
  mov    %rax,(%rdi)
L100:
  mov    %rdx,%rax
  and    $0xfffffffffffffffc,%rax
  add    %rax,%rcx
  add    %r8,%rax
  and    $0x3,%edx
  je     L144
  movzbl (%rcx),%esi
  mov    %sil,(%rax)
  cmp    $0x1,%rdx
  je     L144
  movzbl 0x1(%rcx),%esi
  mov    %sil,0x1(%rax)
  cmp    $0x2,%rdx
  je     L144
  movzbl 0x2(%rcx),%edx
  mov    %dl,0x2(%rax)
  mov    %r8,%rax
  ret
  nopl   0x0(%rax,%rax,1)
L70:
  mov    (%rcx,%rax,8),%rsi
  mov    %rsi,(%r8,%rax,8)
  add    $0x1,%rax
  cmp    %rax,%r9
  jne    L70
  jmp    L100
  nopl   0x0(%rax,%rax,1)
L236:
  xor    %eax,%eax
  nopw   0x0(%rax,%rax,1)
L111:
  movzbl (%rcx,%rax,1),%esi
  mov    %sil,(%r8,%rax,1)
  add    $0x1,%rax
  cmp    %rax,%rdx
  jne    L111
  jmp    L144
L130:
  mov    %r8,%rdi
  mov    %rcx,%r9
  xor    %eax,%eax
  jmp    L270
```

assistant: ```c
void *memcpy(void *dest, const void *src, size_t n) {
  if ((sizeof(unsigned long) - 1) & ((unsigned long)dest | (unsigned long)src)) {
    char *cs = (char *)src;
    char *cd = (char *)dest;
    while (n--)
      *cd++ = *cs++;
  } else {
    long *ls = (long *)src;
    long *ld = (long *)dest;
    size_t cnt = n >> 2;
    while (cnt--)
      *ld++ = *ls++;
    char *cs = (char *)(src + (n & ~0x03));
    char *cd = (char *)(dest + (n & ~0x03));
    cnt = n & 0x3;
    while (cnt--)
      *cd++ = *cs++;
  }
  return dest;
}
```