user: 提供的汇编代码用C语言表示会是什么样子：

```asm
<memrchr>:
  endbr64
  mov    %esi,%r10d
  mov    %rdx,%rcx
  lea    (%rdi,%rdx,1),%rax
  test   %rdx,%rdx
  jne    L60
  jmp    L82
  nopl   0x0(%rax,%rax,1)
L164:
  sub    $0x1,%rax
  cmp    %sil,(%rax)
  je     L16
  sub    $0x1,%rcx
  je     L82
L60:
  test   $0x7,%al
  jne    L164
  movzbl %r10b,%edi
  mov    %edi,%edx
  shl    $0x8,%edx
  or     %edi,%edx
  movslq %edx,%rdx
  mov    %rdx,%r8
  shl    $0x10,%r8
  or     %rdx,%r8
  cmp    $0x7,%rcx
  ja     L159
  jmp    L61
  xchg   %ax,%ax
L269:
  mov    %rdx,%rcx
L159:
  mov    %rax,%r9
  mov    -0x8(%rax),%rdi
  sub    $0x8,%rax
  xor    %r8,%rdi
  lea    0x7efefeff(%rdi),%rdx
  xor    %rdi,%rdx
  or     $0x7efefeff,%rdx
  cmp    $0xffffffffffffffff,%rdx
  je     L173
  cmp    %sil,0x3(%rax)
  je     L138
  cmp    %sil,0x2(%rax)
  je     L56
  cmp    %sil,0x1(%rax)
  je     L231
  cmp    %sil,(%rax)
  je     L16
L173:
  lea    -0x8(%rcx),%rdx
  cmp    $0x7,%rdx
  ja     L269
  sub    $0x9,%rcx
  test   %rdx,%rdx
  je     L82
L124:
  lea    -0x1(%rax),%rdx
  cmp    -0x1(%rax),%r10b
  je     L44
  test   %rcx,%rcx
  je     L82
  lea    -0x2(%rax),%rdx
  cmp    -0x2(%rax),%r10b
  je     L44
  cmp    $0x1,%rcx
  je     L82
  lea    -0x3(%rax),%rdx
  cmp    -0x3(%rax),%r10b
  je     L44
  cmp    $0x2,%rcx
  je     L82
  lea    -0x4(%rax),%rdx
  cmp    -0x4(%rax),%r10b
  je     L44
  cmp    $0x3,%rcx
  je     L82
  lea    -0x5(%rax),%rdx
  cmp    -0x5(%rax),%r10b
  je     L44
  cmp    $0x4,%rcx
  je     L82
  lea    -0x6(%rax),%rdx
  cmp    -0x6(%rax),%r10b
  je     L44
  cmp    $0x5,%rcx
  je     L82
  lea    -0x7(%rax),%rdx
  cmp    %r10b,-0x7(%rax)
  mov    $0x0,%eax
  cmove  %rdx,%rax
  ret
  nop
L16:
  ret
  nopl   0x0(%rax)
L82:
  xor    %eax,%eax
  ret
  nopl   0x0(%rax,%rax,1)
L138:
  lea    -0x5(%r9),%rax
  ret
  nopl   (%rax)
L56:
  lea    -0x6(%r9),%rax
  ret
  nopl   (%rax)
L231:
  lea    -0x7(%r9),%rax
  ret
L44:
  mov    %rdx,%rax
  ret
L61:
  sub    $0x1,%rcx
  jmp    L124
```

assistant: ```c
void *memrchr(const void *s, int c_in, size_t n) {
  const unsigned char *char_ptr;
  const unsigned long int *longword_ptr;
  unsigned long int longword, magic_bits, charmask;
  unsigned char c;
  c = (unsigned char)c_in;
  for (char_ptr = (const unsigned char *)s + n; n > 0 && ((size_t)char_ptr & (sizeof(longword) - 1)) != 0; --n)
    if (*--char_ptr == c)
      return (void *)char_ptr;
  longword_ptr = (const unsigned long int *)char_ptr;
  if (sizeof(longword) != 4 && sizeof(longword) != 8)
    abort();
  magic_bits = 0x7efefeff;
  charmask = c | (c << 8);
  charmask |= charmask << 16;
  while (n >= sizeof(longword)) {
    longword = *--longword_ptr ^ charmask;
    if ((((longword + magic_bits) ^ ~longword) & ~magic_bits) != 0) {
      const unsigned char *cp = (const unsigned char *)longword_ptr;
      if (cp[3] == c)
        return (void *)&cp[3];
      if (cp[2] == c)
        return (void *)&cp[2];
      if (cp[1] == c)
        return (void *)&cp[1];
      if (cp[0] == c)
        return (void *)cp;
    }
    n -= sizeof(longword);
  }
  char_ptr = (const unsigned char *)longword_ptr;
  while (n-- > 0) {
    if (*--char_ptr == c)
      return (void *)char_ptr;
  }
  return 0;
}
```