user: Converte this assembly snippet into its equivalent C code:

```asm
<_permutate>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbx
  sub    $0x88,%rsp
  mov    %rdi,-0x68(%rbp)
  mov    %rsi,-0x70(%rbp)
  mov    %edx,-0x74(%rbp)
  mov    %rcx,-0x80(%rbp)
  mov    %r8,-0x88(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x38(%rbp)
  xor    %eax,%eax
  mov    -0x70(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    %eax,-0x5c(%rbp)
  cmpl   $0x0,-0x5c(%rbp)
  jne    L66
  mov    -0x88(%rbp),%rdx
  mov    -0x68(%rbp),%rax
  mov    -0x80(%rbp),%rcx
  mov    %rdx,%rsi
  mov    %rax,%rdi
  call   *%rcx
  jmp    L55
L66:
  movl   $0x0,-0x60(%rbp)
  jmp    L46
L0:
  mov    %rsp,%rax
  mov    %rax,%rbx
  mov    -0x74(%rbp),%eax
  movslq %eax,%rdx
  sub    $0x1,%rdx
  mov    %rdx,-0x58(%rbp)
  movslq %eax,%rdx
  mov    %rdx,%r12
  mov    $0x0,%r13d
  movslq %eax,%rdx
  mov    %rdx,%r14
  mov    $0x0,%r15d
  cltq
  mov    $0x10,%edx
  sub    $0x1,%rdx
  add    %rdx,%rax
  mov    $0x10,%esi
  mov    $0x0,%edx
  div    %rsi
  imul   $0x10,%rax,%rax
  mov    %rax,%rcx
  and    $0xfffffffffffff000,%rcx
  mov    %rsp,%rdx
  sub    %rcx,%rdx
L39:
  cmp    %rdx,%rsp
  je     L44
  sub    $0x1000,%rsp
  orq    $0x0,0xff8(%rsp)
  jmp    L39
L44:
  mov    %rax,%rdx
  and    $0xfff,%edx
  sub    %rdx,%rsp
  mov    %rax,%rdx
  and    $0xfff,%edx
  test   %rdx,%rdx
  je     L43
  and    $0xfff,%eax
  sub    $0x8,%rax
  add    %rsp,%rax
  orq    $0x0,(%rax)
L43:
  mov    %rsp,%rax
  add    $0x0,%rax
  mov    %rax,-0x50(%rbp)
  mov    -0x74(%rbp),%eax
  movslq %eax,%rdx
  sub    $0x1,%rdx
  mov    %rdx,-0x48(%rbp)
  movslq %eax,%rdx
  mov    %rdx,-0xa0(%rbp)
  movq   $0x0,-0x98(%rbp)
  movslq %eax,%rdx
  mov    %rdx,-0xb0(%rbp)
  movq   $0x0,-0xa8(%rbp)
  cltq
  mov    $0x10,%edx
  sub    $0x1,%rdx
  add    %rdx,%rax
  mov    $0x10,%edi
  mov    $0x0,%edx
  div    %rdi
  imul   $0x10,%rax,%rax
  mov    %rax,%rcx
  and    $0xfffffffffffff000,%rcx
  mov    %rsp,%rdx
  sub    %rcx,%rdx
L34:
  cmp    %rdx,%rsp
  je     L21
  sub    $0x1000,%rsp
  orq    $0x0,0xff8(%rsp)
  jmp    L34
L21:
  mov    %rax,%rdx
  and    $0xfff,%edx
  sub    %rdx,%rsp
  mov    %rax,%rdx
  and    $0xfff,%edx
  test   %rdx,%rdx
  je     L29
  and    $0xfff,%eax
  sub    $0x8,%rax
  add    %rsp,%rax
  orq    $0x0,(%rax)
L29:
  mov    %rsp,%rax
  add    $0x0,%rax
  mov    %rax,-0x40(%rbp)
  mov    -0x74(%rbp),%edx
  mov    -0x50(%rbp),%rax
  mov    $0x0,%esi
  mov    %rax,%rdi
  call   <memset@plt>
  mov    -0x74(%rbp),%edx
  mov    -0x40(%rbp),%rax
  mov    $0x0,%esi
  mov    %rax,%rdi
  call   <memset@plt>
  mov    -0x60(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movsbl %al,%edx
  mov    -0x68(%rbp),%rcx
  mov    -0x50(%rbp),%rax
  mov    %rcx,%rsi
  mov    %rax,%rdi
  call   <str_concat@plt>
  mov    -0x60(%rbp),%edx
  mov    -0x70(%rbp),%rcx
  mov    -0x40(%rbp),%rax
  mov    %rcx,%rsi
  mov    %rax,%rdi
  call   <str_shift@plt>
  mov    -0x88(%rbp),%rdi
  mov    -0x80(%rbp),%rcx
  mov    -0x74(%rbp),%edx
  mov    -0x40(%rbp),%rsi
  mov    -0x50(%rbp),%rax
  mov    %rdi,%r8
  mov    %rax,%rdi
  call   <_permutate>
  mov    %rbx,%rsp
  addl   $0x1,-0x60(%rbp)
L46:
  mov    -0x60(%rbp),%eax
  cmp    -0x5c(%rbp),%eax
  jl     L0
L55:
  nop
  mov    -0x38(%rbp),%rax
  sub    %fs:0x28,%rax
  je     L22
  call   <__stack_chk_fail@plt>
L22:
  lea    -0x28(%rbp),%rsp
  pop    %rbx
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  pop    %rbp
  ret
```

assistant: ```c
void _permutate(char *prefix, char *str, int max_len, void (*callback)(char *, void *), void *data) {
  int len = strlen(str);
  if (len == 0) {
    callback(prefix, data);
  } else {
    for (int i = 0; i < len; i++) {
      char new_prefix[max_len];
      char new_str[max_len];
      memset(new_prefix, '\0', max_len);
      memset(new_str, '\0', max_len);
      str_concat(new_prefix, prefix, str[i]);
      str_shift(new_str, str, i);
      _permutate(new_prefix, new_str, max_len, callback, data);
    }
  }
}
```