user: 下面的汇编指令对应的C源代码是什么：

```asm
<convert>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x40,%rsp
  mov    %rdi,-0x38(%rbp)
  mov    %esi,-0x3c(%rbp)
  mov    -0x38(%rbp),%rax
  mov    %rax,%rdi
  call   <strlen@plt>
  mov    %eax,-0x18(%rbp)
  mov    -0x18(%rbp),%eax
  add    $0x1,%eax
  mov    %eax,%edi
  call   <malloc@plt>
  mov    %rax,-0x8(%rbp)
  movl   $0x0,-0x24(%rbp)
  jmp    L41
L143:
  mov    -0x24(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x8(%rbp),%rax
  add    %rdx,%rax
  movb   $0x0,(%rax)
  addl   $0x1,-0x24(%rbp)
L41:
  mov    -0x18(%rbp),%eax
  cmp    -0x24(%rbp),%eax
  jge    L143
  cmpl   $0x2,-0x3c(%rbp)
  jle    L5
  mov    -0x3c(%rbp),%eax
  sub    $0x1,%eax
  add    %eax,%eax
  jmp    L11
L5:
  mov    -0x3c(%rbp),%eax
L11:
  mov    %eax,-0x14(%rbp)
  movl   $0x0,-0x1c(%rbp)
  movl   $0x0,-0x20(%rbp)
  jmp    L58
L140:
  cmpl   $0x0,-0x20(%rbp)
  je     L125
  mov    -0x3c(%rbp),%eax
  sub    $0x1,%eax
  cmp    %eax,-0x20(%rbp)
  jne    L36
L125:
  movl   $0x0,-0x24(%rbp)
  jmp    L145
L2:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  add    %edx,%eax
  movslq %eax,%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    -0x1c(%rbp),%ecx
  mov    -0x24(%rbp),%edx
  add    %ecx,%edx
  movslq %edx,%rcx
  mov    -0x8(%rbp),%rdx
  add    %rcx,%rdx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  addl   $0x1,-0x24(%rbp)
L145:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  add    %edx,%eax
  cmp    %eax,-0x18(%rbp)
  jg     L2
  mov    -0x24(%rbp),%eax
  add    %eax,-0x1c(%rbp)
  jmp    L45
L36:
  movl   $0x0,-0x24(%rbp)
  jmp    L137
L97:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  add    %edx,%eax
  movslq %eax,%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    -0x24(%rbp),%edx
  lea    (%rdx,%rdx,1),%ecx
  mov    -0x1c(%rbp),%edx
  add    %ecx,%edx
  movslq %edx,%rcx
  mov    -0x8(%rbp),%rdx
  add    %rcx,%rdx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  addl   $0x1,-0x24(%rbp)
L137:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x20(%rbp),%eax
  add    %edx,%eax
  cmp    %eax,-0x18(%rbp)
  jg     L97
  mov    -0x24(%rbp),%eax
  lea    (%rax,%rax,1),%edx
  mov    -0x1c(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x10(%rbp)
  movl   $0x0,-0x24(%rbp)
  jmp    L77
L120:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x14(%rbp),%eax
  add    %edx,%eax
  sub    -0x20(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    -0x24(%rbp),%edx
  lea    (%rdx,%rdx,1),%ecx
  mov    -0x1c(%rbp),%edx
  add    %ecx,%edx
  movslq %edx,%rdx
  lea    0x1(%rdx),%rcx
  mov    -0x8(%rbp),%rdx
  add    %rcx,%rdx
  movzbl (%rax),%eax
  mov    %al,(%rdx)
  addl   $0x1,-0x24(%rbp)
L77:
  mov    -0x24(%rbp),%eax
  imul   -0x14(%rbp),%eax
  mov    %eax,%edx
  mov    -0x14(%rbp),%eax
  add    %edx,%eax
  sub    -0x20(%rbp),%eax
  cmp    %eax,-0x18(%rbp)
  jg     L120
  mov    -0x24(%rbp),%eax
  lea    (%rax,%rax,1),%edx
  mov    -0x1c(%rbp),%eax
  add    %edx,%eax
  add    $0x1,%eax
  mov    %eax,-0xc(%rbp)
  mov    -0xc(%rbp),%edx
  mov    -0x10(%rbp),%eax
  cmp    %eax,%edx
  cmovle %edx,%eax
  mov    %eax,-0x1c(%rbp)
L45:
  addl   $0x1,-0x20(%rbp)
L58:
  mov    -0x20(%rbp),%eax
  cmp    -0x3c(%rbp),%eax
  jl     L140
  mov    -0x8(%rbp),%rax
  leave
  ret
```

assistant: ```c
char *convert(char *s, int num_row) {
  int length = strlen(s);
  char *retval = (char *)malloc(length + 1);
  int i, r, mem, mem1, mem2;
  int num_per_trk;
  for (i = 0; i < length + 1; i++)
    retval[i] = 0;
  num_per_trk = (num_row > 2) ? (2 * num_row - 2) : num_row;
  mem = 0;
  for (r = 0; r < num_row; r++) {
    if (r == 0 || r == num_row - 1) {
      for (i = 0; i * num_per_trk + r < length; i++)
        retval[mem + i] = s[i * num_per_trk + r];
      mem += i;
      continue;
    }
    for (i = 0; i * num_per_trk + r < length; i++)
      retval[mem + i * 2] = s[i * num_per_trk + r];
    mem1 = mem + i * 2;
    for (i = 0; i * num_per_trk + num_per_trk - r < length; i++)
      retval[mem + i * 2 + 1] = s[i * num_per_trk + num_per_trk - r];
    mem2 = mem + i * 2 + 1;
    mem = (mem1 < mem2) ? mem1 : mem2;
  }
  return retval;
}
```