user: 下面的汇编指令对应的C源代码是什么：

```asm
<bitfill_unaligned_rev>:
  endbr64
  test   %r9d,%r9d
  jne    L35
  ret
  nopw   0x0(%rax,%rax,1)
L35:
  push   %r15
  mov    %esi,%r15d
  push   %r14
  mov    %r9d,%r14d
  push   %r13
  mov    %r8d,%r13d
  push   %r12
  mov    %ecx,%r12d
  push   %rbp
  mov    %rdx,%rbp
  push   %rbx
  mov    %rdi,%rbx
  mov    $0xffffffffffffffff,%rdi
  sub    $0x18,%rsp
  call   <FB_SHIFT_HIGH@plt>
  lea    (%r15,%r14,1),%ecx
  xor    %edx,%edx
  mov    $0xffffffffffffffff,%rdi
  mov    %rax,0x8(%rsp)
  mov    %ecx,%eax
  divl   0x50(%rsp)
  mov    %ecx,(%rsp)
  mov    %edx,%esi
  call   <FB_SHIFT_HIGH@plt>
  mov    (%rsp),%ecx
  cmp    0x50(%rsp),%ecx
  not    %rax
  mov    0x8(%rsp),%r8
  mov    %rax,%r9
  ja     L17
  mov    %r8,%rax
  mov    (%rbx),%rsi
  mov    %rbp,%rdi
  and    %r9,%rax
  test   %r9,%r9
  cmovne %rax,%r8
  xor    %rsi,%rdi
  mov    %r8,%rdx
  call   <comp@plt>
  mov    %rax,(%rbx)
L107:
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopw   0x0(%rax,%rax,1)
L17:
  test   %r8,%r8
  jne    L52
L106:
  mov    %r14d,%eax
  xor    %edx,%edx
  divl   0x50(%rsp)
  mov    %eax,%edx
  cmp    $0x3,%eax
  jbe    L70
  lea    -0x4(%rax),%r14d
  shr    $0x2,%r14d
  add    $0x1,%r14d
  shl    $0x5,%r14
  add    %rbx,%r14
  nopl   0x0(%rax,%rax,1)
L75:
  mov    %rbp,%rdi
  mov    %r12d,%ecx
  xor    %rbp,(%rbx)
  shl    %cl,%rdi
  mov    %r13d,%ecx
  shr    %cl,%rbp
  mov    %r12d,%ecx
  or     %rbp,%rdi
  xor    %rdi,0x8(%rbx)
  mov    %rdi,%rbp
  shl    %cl,%rbp
  mov    %r13d,%ecx
  shr    %cl,%rdi
  mov    %r12d,%ecx
  or     %rdi,%rbp
  xor    %rbp,0x10(%rbx)
  add    $0x20,%rbx
  mov    %rbp,%rdx
  shl    %cl,%rdx
  mov    %r13d,%ecx
  shr    %cl,%rbp
  mov    %r12d,%ecx
  or     %rbp,%rdx
  xor    %rdx,-0x8(%rbx)
  mov    %rdx,%rbp
  shl    %cl,%rbp
  mov    %r13d,%ecx
  shr    %cl,%rdx
  or     %rdx,%rbp
  cmp    %r14,%rbx
  jne    L75
  and    $0x3,%eax
  mov    %eax,%edx
L90:
  lea    -0x1(%rdx),%eax
  test   %edx,%edx
  je     L62
  mov    (%r14),%rdx
L96:
  mov    %rbp,%rsi
  mov    %r12d,%ecx
  xor    %rbp,%rdx
  shl    %cl,%rsi
  mov    %r13d,%ecx
  shr    %cl,%rbp
  or     %rsi,%rbp
  sub    $0x1,%eax
  jae    L96
  mov    %rdx,(%r14)
L62:
  test   %r9,%r9
  je     L107
  mov    (%r14),%rsi
  mov    %rbp,%rdi
  mov    %r9,%rdx
  xor    %rsi,%rdi
  call   <comp@plt>
  mov    %rax,(%r14)
  jmp    L107
  xchg   %ax,%ax
L52:
  mov    (%rbx),%rsi
  mov    %r8,%rdx
  mov    %rax,(%rsp)
  add    $0x8,%rbx
  mov    %rsi,%rdi
  xor    %rbp,%rdi
  call   <comp@plt>
  mov    %r12d,%ecx
  mov    (%rsp),%r9
  mov    %rax,-0x8(%rbx)
  mov    %rbp,%rax
  shl    %cl,%rax
  mov    %r13d,%ecx
  shr    %cl,%rbp
  or     %rax,%rbp
  mov    0x50(%rsp),%eax
  sub    %r15d,%eax
  sub    %eax,%r14d
  jmp    L106
  nopw   0x0(%rax,%rax,1)
L70:
  mov    %rbx,%r14
  jmp    L90
```

assistant: ```c
void bitfill_unaligned_rev(unsigned long *dst, int dst_idx, unsigned long pat, int left, int right, unsigned n, int bits) {
  unsigned long first, last;
  if (!n)
    return;
  first = FB_SHIFT_HIGH(~0UL, dst_idx);
  last = ~(FB_SHIFT_HIGH(~0UL, (dst_idx + n) % bits));
  if (dst_idx + n <= bits) {
    if (last)
      first &= last;
    *dst = comp(*dst ^ pat, *dst, first);
  } else {
    if (first != 0UL) {
      *dst = comp(*dst ^ pat, *dst, first);
      dst++;
      pat = pat << left | pat >> right;
      n -= bits - dst_idx;
    }
    n /= bits;
    while (n >= 4) {
      *dst++ ^= pat;
      pat = pat << left | pat >> right;
      *dst++ ^= pat;
      pat = pat << left | pat >> right;
      *dst++ ^= pat;
      pat = pat << left | pat >> right;
      *dst++ ^= pat;
      pat = pat << left | pat >> right;
      n -= 4;
    }
    while (n--) {
      *dst ^= pat;
      pat = pat << left | pat >> right;
    }
    if (last)
      *dst = comp(*dst ^ pat, *dst, last);
  }
}
```