user: 提供的汇编代码用C语言表示会是什么样子:

```asm
<rec>:
  endbr64
  push   %r15
  movsbl %cl,%r11d
  push   %r14
  mov    %r9,%r14
  push   %r13
  mov    %rdi,%r13
  push   %r12
  mov    %rsi,%r12
  mov    %edx,%esi
  push   %rbp
  mov    %r8d,%ebp
  push   %rbx
  sub    $0x18,%rsp
  test   %edx,%edx
  jne    L5
  cmp    %rbp,%r12
  jb     L21
  mov    %r12,%rax
  xor    %edx,%edx
  mov    %rdi,%rbx
  div    %rbp
  mov    %rax,%r15
  cmp    %rbp,%rax
  jae    L111
L27:
  mov    %esi,%edx
  mov    %r13,%rdi
  mov    %r11d,%esi
  call   <memset@plt>
L73:
  mov    %r15,%rax
  xor    %edx,%edx
  add    $0x1,%rbx
  div    %rbp
  movzbl (%r14,%rdx,1),%eax
  mov    %al,-0x1(%rbx)
  sub    %r13d,%ebx
  add    %r13,%rbx
  jmp    L188
  nopl   0x0(%rax)
L5:
  lea    -0x1(%rdx),%edi
  cmp    %rbp,%r12
  jae    L153
  mov    %edi,%ebx
  mov    %edi,%esi
  add    %r13,%rbx
L2:
  mov    %esi,%edx
  mov    %r13,%rdi
  mov    %r11d,%esi
  call   <memset@plt>
L188:
  mov    %r12,%rax
  xor    %edx,%edx
  div    %rbp
  movzbl (%r14,%rdx,1),%eax
  mov    %al,(%rbx)
  add    $0x18,%rsp
  lea    0x1(%rbx),%rax
  sub    %r13d,%eax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nopl   0x0(%rax)
L153:
  mov    %r12,%rax
  xor    %edx,%edx
  div    %rbp
  mov    %rax,%r15
  test   %edi,%edi
  je     L45
  lea    -0x2(%rsi),%edi
  cmp    %rbp,%rax
  jb     L197
  xor    %edx,%edx
  div    %rbp
  mov    %rax,%rbx
  test   %edi,%edi
  je     L114
  lea    -0x3(%rsi),%r10d
  cmp    %rbp,%rax
  jae    L23
  mov    %r10d,%r8d
  add    %r13,%r8
L100:
  mov    %r10d,%edx
  mov    %r11d,%esi
  mov    %r13,%rdi
  mov    %r8,(%rsp)
  call   <memset@plt>
  mov    (%rsp),%r8
L124:
  mov    %rbx,%rax
  xor    %edx,%edx
  add    $0x1,%r8
  div    %rbp
  movzbl (%r14,%rdx,1),%eax
  mov    %al,-0x1(%r8)
  sub    %r13d,%r8d
  lea    0x0(%r13,%r8,1),%rbx
  jmp    L73
  nopw   0x0(%rax,%rax,1)
L21:
  mov    %rdi,%rbx
  jmp    L2
L45:
  cmp    %rbp,%rax
  jb     L150
L111:
  xor    %edx,%edx
  div    %rbp
  mov    %rax,%rbx
L114:
  cmp    %rbp,%rbx
  jb     L3
  mov    %rbx,%rax
  xor    %edx,%edx
  xor    %r10d,%r10d
  div    %rbp
  mov    %rax,(%rsp)
L33:
  cmp    %rbp,%rax
  jb     L39
  xor    %edx,%edx
  mov    %r14,%r9
  mov    %r11d,%ecx
  mov    %r13,%rdi
  div    %rbp
  mov    %r10d,%edx
  mov    %rax,%rsi
  call   <rec>
  mov    %eax,%r8d
  add    %r13,%r8
L92:
  mov    (%rsp),%rax
  xor    %edx,%edx
  add    $0x1,%r8
  div    %rbp
  movzbl (%r14,%rdx,1),%eax
  mov    %al,-0x1(%r8)
  sub    %r13d,%r8d
  add    %r13,%r8
  jmp    L124
  xchg   %ax,%ax
L197:
  mov    %edi,%ebx
  mov    %edi,%esi
  add    %r13,%rbx
  jmp    L27
  nopl   0x0(%rax)
L23:
  xor    %edx,%edx
  sub    $0x4,%esi
  div    %rbp
  test   %r10d,%r10d
  cmovne %esi,%r10d
  mov    %rax,(%rsp)
  jmp    L33
  nopl   (%rax)
L39:
  mov    %r10d,%edx
  mov    %r11d,%esi
  mov    %r13,%rdi
  mov    %r10d,0xc(%rsp)
  call   <memset@plt>
  mov    0xc(%rsp),%r8d
  add    %r13,%r8
  jmp    L92
  nopl   (%rax)
L3:
  mov    %r13,%r8
  xor    %r10d,%r10d
  jmp    L100
  nopl   0x0(%rax,%rax,1)
L150:
  mov    %r13,%rbx
  xor    %esi,%esi
  jmp    L27
```

assistant: ```c
unsigned rec(char *buffer, unsigned long long num, unsigned width, char pad, unsigned base, const char *digits) {
  char *s = buffer;
  if (width)
    --width;
  if (num >= base)
    s += rec(s, num / base, width, pad, base, digits);
  else {
    memset(s, pad, width);
    s += width;
  }
  *s++ = digits[num % base];
  return s - buffer;
}
```