user: What would the C source look like for the assembly code provided here:

```asm
<convert_old>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x18(%rbp)
  mov    %rsi,-0x20(%rbp)
  mov    %edx,-0x24(%rbp)
  mov    %ecx,-0x28(%rbp)
  cmpl   $0x0,-0x28(%rbp)
  je     L43
  movl   $0x0,-0x8(%rbp)
  mov    -0x24(%rbp),%eax
  sub    $0x8,%eax
  mov    %eax,-0x4(%rbp)
  jmp    L47
L25:
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%edx
  mov    -0x4(%rbp),%eax
  movslq %eax,%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  shr    $0x7,%dl
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x6,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x1(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x5,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x2(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x4,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x3(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x3,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x4(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x2,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x5(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    %eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x6(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x7(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  addl   $0x1,-0x8(%rbp)
  subl   $0x8,-0x4(%rbp)
L47:
  mov    -0x24(%rbp),%eax
  lea    0x7(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x3,%eax
  cmp    %eax,-0x8(%rbp)
  jl     L25
  jmp    L38
L43:
  movl   $0x0,-0x8(%rbp)
  movl   $0x0,-0x4(%rbp)
  jmp    L8
L6:
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%edx
  mov    -0x4(%rbp),%eax
  movslq %eax,%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    %eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x1(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x2,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x2(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x3,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x3(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x4,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x4(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x5,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x5(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%eax
  movzbl %al,%eax
  sar    $0x6,%eax
  mov    %eax,%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x6(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  and    $0x1,%edx
  mov    %dl,(%rax)
  mov    -0x8(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x18(%rbp),%rax
  add    %rdx,%rax
  movzbl (%rax),%edx
  mov    -0x4(%rbp),%eax
  cltq
  lea    0x7(%rax),%rcx
  mov    -0x20(%rbp),%rax
  add    %rcx,%rax
  shr    $0x7,%dl
  mov    %dl,(%rax)
  addl   $0x1,-0x8(%rbp)
  addl   $0x8,-0x4(%rbp)
L8:
  mov    -0x24(%rbp),%eax
  lea    0x7(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x3,%eax
  cmp    %eax,-0x8(%rbp)
  jl     L6
L38:
  nop
  pop    %rbp
  ret
```

assistant: ```c
void convert_old(unsigned char *rec, unsigned char *data, int numchan, int decreasing_f) {
  int ii, jj;
  if (decreasing_f) {
    for (ii = 0, jj = numchan - 8; ii < numchan / 8; ii++, jj -= 8) {
      data[jj] = rec[ii] & 0x80 ? 1 : 0;
      data[jj + 1] = rec[ii] & 0x40 ? 1 : 0;
      data[jj + 2] = rec[ii] & 0x20 ? 1 : 0;
      data[jj + 3] = rec[ii] & 0x10 ? 1 : 0;
      data[jj + 4] = rec[ii] & 0x08 ? 1 : 0;
      data[jj + 5] = rec[ii] & 0x04 ? 1 : 0;
      data[jj + 6] = rec[ii] & 0x02 ? 1 : 0;
      data[jj + 7] = rec[ii] & 0x01 ? 1 : 0;
    }
  } else {
    for (ii = 0, jj = 0; ii < numchan / 8; ii++, jj += 8) {
      data[jj] = rec[ii] & 0x01 ? 1 : 0;
      data[jj + 1] = rec[ii] & 0x02 ? 1 : 0;
      data[jj + 2] = rec[ii] & 0x04 ? 1 : 0;
      data[jj + 3] = rec[ii] & 0x08 ? 1 : 0;
      data[jj + 4] = rec[ii] & 0x10 ? 1 : 0;
      data[jj + 5] = rec[ii] & 0x20 ? 1 : 0;
      data[jj + 6] = rec[ii] & 0x40 ? 1 : 0;
      data[jj + 7] = rec[ii] & 0x80 ? 1 : 0;
    }
  }
}
```