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

```asm
<Concatenate2>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbx
  sub    $0x68,%rsp
  mov    %rdi,-0x78(%rbp)
  mov    %rsi,-0x80(%rbp)
  mov    %rdx,-0x88(%rbp)
  mov    %ecx,-0x8c(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x38(%rbp)
  xor    %eax,%eax
  mov    %rsp,%rax
  mov    %rax,%rbx
  mov    -0x80(%rbp),%rax
  mov    %rax,%rdi
  call   <GetStringLength@plt>
  mov    %eax,-0x54(%rbp)
  mov    -0x88(%rbp),%rax
  mov    %rax,%rdi
  call   <GetStringLength@plt>
  mov    %eax,-0x50(%rbp)
  cmpl   $0x0,-0x54(%rbp)
  js     L217
  cmpl   $0x0,-0x50(%rbp)
  jns    L25
L217:
  mov    -0x78(%rbp),%rax
  mov    %rax,%rdi
  call   <ReturnNullMallocStack@plt>
  jmp    L218
L25:
  mov    -0x8c(%rbp),%eax
  mov    %eax,-0x64(%rbp)
  cmpl   $0xffffffff,-0x64(%rbp)
  jne    L120
  mov    -0x54(%rbp),%eax
  mov    %eax,-0x64(%rbp)
L120:
  mov    -0x64(%rbp),%eax
  cmp    -0x54(%rbp),%eax
  jg     L173
  cmpl   $0x0,-0x64(%rbp)
  jns    L22
L173:
  mov    -0x78(%rbp),%rax
  mov    %rax,%rdi
  call   <ReturnNullMallocStack@plt>
  jmp    L218
L22:
  mov    -0x64(%rbp),%edx
  mov    -0x50(%rbp),%eax
  add    %edx,%eax
  sub    -0x54(%rbp),%eax
  mov    %eax,-0x60(%rbp)
  cmpl   $0x0,-0x60(%rbp)
  jns    L157
  movl   $0x0,-0x60(%rbp)
L157:
  cmpl   $0x0,-0x60(%rbp)
  jns    L106
  mov    -0x50(%rbp),%eax
  jmp    L40
L106:
  mov    -0x60(%rbp),%eax
L40:
  mov    -0x54(%rbp),%edx
  add    %edx,%eax
  mov    %eax,-0x4c(%rbp)
  mov    -0x4c(%rbp),%eax
  lea    D9(%rip),%rdx
  mov    %rdx,%rsi
  mov    %eax,%edi
  call   <GetStackSize@plt>
  movslq %eax,%rdx
  sub    $0x1,%rdx
  mov    %rdx,-0x48(%rbp)
  movslq %eax,%rdx
  mov    %rdx,%r14
  mov    $0x0,%r15d
  movslq %eax,%rdx
  mov    %rdx,%r12
  mov    $0x0,%r13d
  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
L154:
  cmp    %rdx,%rsp
  je     L167
  sub    $0x1000,%rsp
  orq    $0x0,0xff8(%rsp)
  jmp    L154
L167:
  mov    %rax,%rdx
  and    $0xfff,%edx
  sub    %rdx,%rsp
  mov    %rax,%rdx
  and    $0xfff,%edx
  test   %rdx,%rdx
  je     L185
  and    $0xfff,%eax
  sub    $0x8,%rax
  add    %rsp,%rax
  orq    $0x0,(%rax)
L185:
  mov    %rsp,%rax
  add    $0x0,%rax
  mov    %rax,-0x40(%rbp)
  movl   $0x0,-0x5c(%rbp)
  movl   $0xffffffff,-0x58(%rbp)
  movl   $0x0,-0x5c(%rbp)
  jmp    L27
L84:
  cmpl   $0xffffffff,-0x58(%rbp)
  jne    L44
  mov    -0x5c(%rbp),%eax
  cmp    -0x64(%rbp),%eax
  jne    L44
  movl   $0x0,-0x58(%rbp)
  jmp    L229
L44:
  mov    -0x58(%rbp),%eax
  cmp    -0x50(%rbp),%eax
  jne    L229
  movl   $0xffffffff,-0x58(%rbp)
L229:
  cmpl   $0xffffffff,-0x58(%rbp)
  jne    L222
  mov    -0x5c(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x80(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  jmp    L98
L222:
  mov    -0x58(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x88(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
L98:
  mov    -0x40(%rbp),%rcx
  mov    -0x5c(%rbp),%edx
  movslq %edx,%rdx
  mov    %al,(%rcx,%rdx,1)
  cmpl   $0xffffffff,-0x58(%rbp)
  je     L83
  addl   $0x1,-0x58(%rbp)
L83:
  addl   $0x1,-0x5c(%rbp)
L27:
  mov    -0x5c(%rbp),%eax
  cmp    -0x4c(%rbp),%eax
  jl     L84
  mov    -0x40(%rbp),%rdx
  mov    -0x5c(%rbp),%eax
  cltq
  movb   $0x0,(%rdx,%rax,1)
  mov    -0x5c(%rbp),%edx
  mov    -0x40(%rbp),%rcx
  mov    -0x78(%rbp),%rax
  mov    %rcx,%rsi
  mov    %rax,%rdi
  call   <ReturnOutputMallocStack@plt>
L218:
  mov    %rbx,%rsp
  mov    -0x38(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L153
  call   <__stack_chk_fail@plt>
L153:
  lea    -0x28(%rbp),%rsp
  pop    %rbx
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  pop    %rbp
  ret
```

tool_calls: name: read_data
arguments: tag: D9
datatype: string

tool: D9: char

assistant: ```c
char *Concatenate2(char *output, char *first, char *second, const int startI) {
  int length1 = GetStringLength(first);
  int length2 = GetStringLength(second);
  if (length1 < 0 || length2 < 0) {
    return ReturnNullMallocStack(output);
  }
  int startI2 = startI;
  if (startI2 == -1)
    startI2 = length1;
  if (startI2 > length1 || startI2 < 0) {
    return ReturnNullMallocStack(output);
  }
  int extra = startI2 + length2 - length1;
  if (extra < 0)
    extra = 0;
  int length0 = length1 + (extra < 0 ? length2 : extra);
  char output2[GetStackSize(length0, "char")];
  int i = 0;
  int i2 = -1;
  for (i = 0; i < length0; i++) {
    if (i2 == -1 && i == startI2)
      i2 = 0;
    else if (i2 == length2)
      i2 = -1;
    output2[i] = (i2 == -1 ? first[i] : second[i2]);
    if (i2 != -1)
      i2++;
  }
  output2[i] = '\0';
  return ReturnOutputMallocStack(output, output2, i);
}
```