user: 下面的汇编指令对应的C源代码是什么：

```asm
<strtoul>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x18,%rsp
  mov    %rdi,%r13
  mov    %rsi,%r14
  mov    %edx,%r12d
  test   %rdi,%rdi
  setne  %dil
  movzbl %dil,%edi
  call   <assert@plt>
  lea    -0x2(%r12),%eax
  cmp    $0x22,%eax
  jbe    L170
  test   %r12d,%r12d
  je     L170
  mov    D38(%rip),%rax
  mov    (%rax),%edx
  mov    D12(%rip),%rax
  mov    %edx,(%rax)
  mov    $0x0,%eax
  test   %r14,%r14
  je     L255
  mov    %r13,(%r14)
  jmp    L255
L170:
  mov    %r13,%rbp
L275:
  mov    %rbp,%r15
  add    $0x1,%rbp
  movzbl -0x1(%rbp),%ebx
  movzbl %bl,%edi
  call   <isspace@plt>
  test   %rax,%rax
  jne    L275
  cmp    $0x2d,%bl
  je     L332
  movl   $0x0,0xc(%rsp)
  cmp    $0x2b,%bl
  je     L75
L184:
  test   $0xffffffef,%r12d
  jne    L233
  cmp    $0x30,%bl
  je     L90
L233:
  test   %r12d,%r12d
  jne    L95
  cmp    $0x30,%bl
  setne  %r12b
  movzbl %r12b,%r12d
  lea    0x8(%r12,%r12,1),%r12d
L95:
  mov    D29(%rip),%rax
  mov    (%rax),%r8
  movslq %r12d,%r11
  mov    %r8,%rax
  mov    $0x0,%edx
  div    %r11
  mov    %rax,%rdi
  mov    D14(%rip),%rax
  mov    (%rax),%r10d
  mov    $0x0,%esi
  mov    $0x0,%eax
  mov    $0xffffffff,%r9d
  mov    $0x1,%r15d
  jmp    L150
L332:
  movzbl 0x0(%rbp),%ebx
  lea    0x2(%r15),%rbp
  movl   $0x1,0xc(%rsp)
  jmp    L184
L75:
  movzbl 0x0(%rbp),%ebx
  lea    0x2(%r15),%rbp
  jmp    L184
L90:
  movzbl 0x0(%rbp),%eax
  and    $0xffffffdf,%eax
  cmp    $0x58,%al
  jne    L233
  movzbl 0x1(%rbp),%eax
  lea    -0x30(%rax),%edx
  cmp    $0x9,%dl
  jbe    L94
  mov    %eax,%edx
  and    $0xffffffdf,%edx
  sub    $0x41,%edx
  cmp    $0x5,%dl
  ja     L233
L94:
  add    $0x2,%rbp
  mov    %eax,%ebx
  mov    $0x10,%r12d
  jmp    L95
L283:
  lea    -0x61(%rbx),%ecx
  cmp    $0x19,%cl
  ja     L18
  movzbl %bl,%ebx
  sub    $0x57,%ebx
  jmp    L245
L18:
  lea    -0x41(%rbx),%ecx
  cmp    $0x19,%cl
  ja     L316
  movzbl %bl,%ebx
  sub    $0x37,%ebx
  jmp    L245
L223:
  mov    D12(%rip),%rax
  mov    %r10d,(%rax)
  mov    %r8,%rax
  mov    %r9d,%esi
L176:
  add    $0x1,%rbp
  movzbl -0x1(%rbp),%ebx
L150:
  lea    -0x30(%rbx),%ecx
  cmp    $0x9,%cl
  ja     L283
  movzbl %bl,%ebx
  sub    $0x30,%ebx
L245:
  cmp    %ebx,%r12d
  jle    L316
  test   %esi,%esi
  js     L176
  cmp    %rdi,%rax
  ja     L223
  jne    L34
  cmp    %edx,%ebx
  jg     L223
L34:
  imul   %r11,%rax
  movslq %ebx,%rbx
  add    %rbx,%rax
  mov    %r15d,%esi
  jmp    L176
L316:
  cmpl   $0x0,0xc(%rsp)
  je     L339
  test   %esi,%esi
  jle    L339
  neg    %rax
  test   %r14,%r14
  je     L255
L92:
  lea    -0x1(%rbp),%r13
L149:
  mov    %r13,(%r14)
L255:
  add    $0x18,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L339:
  test   %r14,%r14
  je     L255
  test   %esi,%esi
  je     L149
  jmp    L92
```

assistant: ```c
unsigned long int strtoul(const char *nptr, char **endptr, int base) {
  const char *s;
  unsigned long int acc, cutoff;
  unsigned char c;
  int i, neg, any, cutlim;
  assert(nptr != NULL);
  if (base && (base < 2 || base > 36)) {
    errno = EINVAL;
    if (endptr != NULL)
      *endptr = (char *)(nptr);
    return 0;
  }
  s = nptr;
  do {
    c = *s++;
  } while (isspace(c));
  if (c == '-') {
    neg = 1;
    c = *s++;
  } else {
    neg = 0;
    if (c == '+')
      c = *s++;
  }
  if ((base == 0 || base == 16) && c == '0' && (*s == 'x' || *s == 'X') && ((s[1] >= '0' && s[1] <= '9') || (s[1] >= 'a' && s[1] <= 'f') || (s[1] >= 'A' && s[1] <= 'F'))) {
    c = s[1];
    s += 2;
    base = 16;
  } else if (base == 0)
    base = (c == '0' ? 8 : 10);
  cutoff = ((unsigned long int)ULONG_MAX / (unsigned long int)base);
  cutlim = (int)((unsigned long int)ULONG_MAX % (unsigned long int)base);
  for (acc = 0, any = 0;; c = *s++) {
    if (c >= '0' && c <= '9')
      i = c - '0';
    else if (c >= 'a' && c <= 'z')
      i = (c - 'a') + 10;
    else if (c >= 'A' && c <= 'Z')
      i = (c - 'A') + 10;
    else
      break;
    if (i >= base)
      break;
    if (any < 0)
      continue;
    if (acc > cutoff || (acc == cutoff && i > cutlim)) {
      acc = ULONG_MAX;
      any = -1;
      errno = ERANGE;
    } else {
      any = 1;
      acc *= (unsigned long int)base;
      acc += i;
    }
  }
  if (neg && any > 0)
    acc = -acc;
  if (endptr != NULL)
    *endptr = (char *)(any ? s - 1 : nptr);
  return (acc);
}
```