user: 请从给定的汇编指令推导出C源代码:

```asm
<strtoull>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x50,%rsp
  mov    %rdi,-0x38(%rbp)
  mov    %rsi,-0x40(%rbp)
  mov    %edx,-0x44(%rbp)
  mov    -0x38(%rbp),%rax
  mov    %rax,-0x18(%rbp)
L245:
  mov    -0x18(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x18(%rbp)
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,-0x28(%rbp)
  mov    -0x28(%rbp),%eax
  mov    %eax,%edi
  call   <isspace@plt>
  test   %rax,%rax
  jne    L245
  cmpl   $0x2d,-0x28(%rbp)
  jne    L153
  movl   $0x1,-0x24(%rbp)
  mov    -0x18(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x18(%rbp)
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,-0x28(%rbp)
  jmp    L97
L153:
  movl   $0x0,-0x24(%rbp)
  cmpl   $0x2b,-0x28(%rbp)
  jne    L97
  mov    -0x18(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x18(%rbp)
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,-0x28(%rbp)
L97:
  cmpl   $0x0,-0x44(%rbp)
  je     L132
  cmpl   $0x10,-0x44(%rbp)
  jne    L7
L132:
  cmpl   $0x30,-0x28(%rbp)
  jne    L7
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x78,%al
  je     L258
  mov    -0x18(%rbp),%rax
  movzbl (%rax),%eax
  cmp    $0x58,%al
  jne    L7
L258:
  mov    -0x18(%rbp),%rax
  add    $0x1,%rax
  movzbl (%rax),%eax
  movsbl %al,%eax
  mov    %eax,-0x28(%rbp)
  addq   $0x2,-0x18(%rbp)
  movl   $0x10,-0x44(%rbp)
L7:
  cmpl   $0x0,-0x44(%rbp)
  jne    L138
  cmpl   $0x30,-0x28(%rbp)
  jne    L26
  mov    $0x8,%eax
  jmp    L90
L26:
  mov    $0xa,%eax
L90:
  mov    %eax,-0x44(%rbp)
L138:
  mov    D7(%rip),%rax
  mov    (%rax),%rax
  mov    -0x44(%rbp),%edx
  movslq %edx,%rsi
  mov    $0x0,%edx
  div    %rsi
  mov    %rax,-0x8(%rbp)
  mov    D7(%rip),%rax
  mov    (%rax),%rax
  mov    -0x44(%rbp),%edx
  movslq %edx,%rcx
  mov    $0x0,%edx
  div    %rcx
  mov    %rdx,%rax
  mov    %eax,-0x1c(%rbp)
  movq   $0x0,-0x10(%rbp)
  movl   $0x0,-0x20(%rbp)
L165:
  mov    -0x28(%rbp),%eax
  mov    %eax,%edi
  call   <isdigit@plt>
  test   %rax,%rax
  je     L267
  subl   $0x30,-0x28(%rbp)
  jmp    L54
L267:
  mov    -0x28(%rbp),%eax
  mov    %eax,%edi
  call   <isalpha@plt>
  test   %rax,%rax
  je     L67
  mov    -0x28(%rbp),%eax
  mov    %eax,%edi
  call   <isupper@plt>
  test   %rax,%rax
  je     L257
  mov    $0x37,%eax
  jmp    L148
L257:
  mov    $0x57,%eax
L148:
  sub    %eax,-0x28(%rbp)
L54:
  mov    -0x28(%rbp),%eax
  cmp    -0x44(%rbp),%eax
  jge    L68
  cmpl   $0x0,-0x20(%rbp)
  js     L23
  mov    -0x10(%rbp),%rax
  cmp    -0x8(%rbp),%rax
  ja     L93
  mov    -0x10(%rbp),%rax
  cmp    -0x8(%rbp),%rax
  jne    L19
  mov    -0x28(%rbp),%eax
  cmp    -0x1c(%rbp),%eax
  jle    L19
L93:
  movl   $0xffffffff,-0x20(%rbp)
  mov    D7(%rip),%rax
  mov    (%rax),%rax
  mov    %rax,-0x10(%rbp)
  mov    D21(%rip),%rax
  mov    (%rax),%edx
  mov    D32(%rip),%rax
  mov    %edx,(%rax)
  jmp    L141
L19:
  movl   $0x1,-0x20(%rbp)
  mov    -0x44(%rbp),%eax
  cltq
  mov    -0x10(%rbp),%rdx
  imul   %rdx,%rax
  mov    %rax,-0x10(%rbp)
  mov    -0x28(%rbp),%eax
  cltq
  add    %rax,-0x10(%rbp)
  jmp    L141
L23:
  nop
L141:
  mov    -0x18(%rbp),%rax
  lea    0x1(%rax),%rdx
  mov    %rdx,-0x18(%rbp)
  movzbl (%rax),%eax
  movzbl %al,%eax
  mov    %eax,-0x28(%rbp)
  jmp    L165
L67:
  nop
  jmp    L234
L68:
  nop
L234:
  cmpl   $0x0,-0x24(%rbp)
  je     L37
  cmpl   $0x0,-0x20(%rbp)
  jle    L37
  negq   -0x10(%rbp)
L37:
  cmpq   $0x0,-0x40(%rbp)
  je     L27
  cmpl   $0x0,-0x20(%rbp)
  je     L87
  mov    -0x18(%rbp),%rax
  sub    $0x1,%rax
  jmp    L188
L87:
  mov    -0x38(%rbp),%rax
L188:
  mov    -0x40(%rbp),%rdx
  mov    %rax,(%rdx)
L27:
  mov    -0x10(%rbp),%rax
  leave
  ret
```

assistant: ```c
unsigned long long int strtoull(const char *nptr, char **endptr, int base) {
  const char *s;
  unsigned long long int acc, cutoff;
  int c;
  int neg, any, cutlim;
  s = nptr;
  do {
    c = (unsigned char)*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')) {
    c = s[1];
    s += 2;
    base = 16;
  }
  if (base == 0)
    base = c == '0' ? 8 : 10;
  cutoff = ULLONG_MAX / (unsigned long long)base;
  cutlim = ULLONG_MAX % (unsigned long long)base;
  for (acc = 0, any = 0;; c = (unsigned char)*s++) {
    if (isdigit(c))
      c -= '0';
    else if (isalpha(c))
      c -= isupper(c) ? 'A' - 10 : 'a' - 10;
    else
      break;
    if (c >= base)
      break;
    if (any < 0)
      continue;
    if (acc > cutoff || (acc == cutoff && c > cutlim)) {
      any = -1;
      acc = ULLONG_MAX;
      errno = ERANGE;
    } else {
      any = 1;
      acc *= (unsigned long long)base;
      acc += c;
    }
  }
  if (neg && any > 0)
    acc = -acc;
  if (endptr != 0)
    *endptr = (char *)(any ? s - 1 : nptr);
  return (acc);
}
```