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

```asm
<strcat_p>:
  endbr64
  push   %r13
  mov    %rdi,%r13
  push   %r12
  push   %rbp
  mov    %rsi,%rbp
  push   %rbx
  sub    $0x8,%rsp
  call   <stringLength_p@plt>
  mov    %rbp,%rdi
  mov    %eax,%ebx
  call   <stringLength_p@plt>
  lea    (%rbx,%rax,1),%r12d
  mov    %r12d,%edi
  call   <malloc@plt>
  mov    %rax,%r8
  test   %ebx,%ebx
  jle    L174
  lea    0x1(%r13),%rcx
  mov    %r8,%rdx
  lea    -0x1(%rbx),%eax
  mov    %ebx,%esi
  sub    %rcx,%rdx
  cmp    $0xe,%rdx
  jbe    L6
  cmp    $0x6,%eax
  jbe    L6
  cmp    $0xe,%eax
  jbe    L113
  mov    %ebx,%edx
  xor    %eax,%eax
  shr    $0x4,%edx
  shl    $0x4,%rdx
L99:
  movdqu 0x0(%r13,%rax,1),%xmm0
  movups %xmm0,(%r8,%rax,1)
  add    $0x10,%rax
  cmp    %rdx,%rax
  jne    L99
  mov    %ebx,%eax
  and    $0xfffffff0,%eax
  mov    %eax,%ecx
  lea    0x0(%r13,%rcx,1),%rdx
  cmp    %eax,%ebx
  je     L137
  mov    %ebx,%esi
  sub    %eax,%esi
  lea    -0x1(%rsi),%edi
  cmp    $0x6,%edi
  jbe    L150
L129:
  mov    0x0(%r13,%rcx,1),%rdi
  mov    %rdi,(%r8,%rcx,1)
  mov    %esi,%ecx
  and    $0xfffffff8,%ecx
  mov    %ecx,%edi
  add    %ecx,%eax
  add    %rdi,%rdx
  cmp    %ecx,%esi
  je     L137
L150:
  movzbl (%rdx),%esi
  movslq %eax,%rcx
  mov    %sil,(%r8,%rcx,1)
  lea    0x1(%rax),%ecx
  cmp    %ecx,%ebx
  jle    L137
  movzbl 0x1(%rdx),%esi
  movslq %ecx,%rcx
  mov    %sil,(%r8,%rcx,1)
  lea    0x2(%rax),%ecx
  cmp    %ecx,%ebx
  jle    L137
  movzbl 0x2(%rdx),%esi
  movslq %ecx,%rcx
  mov    %sil,(%r8,%rcx,1)
  lea    0x3(%rax),%ecx
  cmp    %ecx,%ebx
  jle    L137
  movzbl 0x3(%rdx),%esi
  movslq %ecx,%rcx
  mov    %sil,(%r8,%rcx,1)
  lea    0x4(%rax),%ecx
  cmp    %ecx,%ebx
  jle    L137
  movzbl 0x4(%rdx),%esi
  movslq %ecx,%rcx
  mov    %sil,(%r8,%rcx,1)
  lea    0x5(%rax),%ecx
  cmp    %ecx,%ebx
  jle    L137
  movzbl 0x5(%rdx),%esi
  movslq %ecx,%rcx
  add    $0x6,%eax
  mov    %sil,(%r8,%rcx,1)
  cmp    %eax,%ebx
  jle    L137
  movzbl 0x6(%rdx),%edx
  cltq
  mov    %dl,(%r8,%rax,1)
L137:
  movslq %ebx,%rax
L0:
  sub    %rax,%rbp
  nopl   0x0(%rax)
L55:
  mov    %eax,%edx
  cmp    %eax,%r12d
  jle    L89
  movzbl 0x0(%rbp,%rax,1),%edx
  mov    %dl,(%r8,%rax,1)
  lea    0x1(%rax),%edx
  add    $0x1,%rax
  cmp    %eax,%ebx
  jle    L55
L89:
  movslq %edx,%rdx
  mov    %r8,%rax
  movb   $0x0,(%r8,%rdx,1)
  add    $0x8,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nopl   0x0(%rax)
L6:
  mov    %ebx,%ecx
  xor    %eax,%eax
  nopl   0x0(%rax)
L8:
  movzbl 0x0(%r13,%rax,1),%edx
  mov    %dl,(%r8,%rax,1)
  add    $0x1,%rax
  cmp    %rcx,%rax
  jne    L8
  jmp    L137
  nopl   (%rax)
L174:
  xor    %eax,%eax
  jmp    L0
L113:
  mov    %r13,%rdx
  xor    %eax,%eax
  xor    %ecx,%ecx
  jmp    L129
```

assistant: ```c
char *strcat_p(char *destinationStr, char *appendingStr) {
  int lengthDest = stringLength_p(destinationStr);
  int lengthApp = stringLength_p(appendingStr);
  char *result = malloc((lengthDest + lengthApp) * sizeof(char));
  int index = 0;
  while (index < lengthDest) {
    result[index] = *destinationStr;
    index++;
    destinationStr++;
  }
  while (index >= lengthDest && index < (lengthApp + lengthDest)) {
    result[index] = *appendingStr;
    index++;
    appendingStr++;
  }
  result[index] = '\0';
  return result;
}
```