user: Please show me the C implementation that matches the assembly code listed below:

```asm
<cftfsub>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  add    $0xffffffffffffff80,%rsp
  mov    %edi,-0x64(%rbp)
  mov    %rsi,-0x70(%rbp)
  mov    %rdx,-0x78(%rbp)
  movl   $0x2,-0x50(%rbp)
  cmpl   $0x8,-0x64(%rbp)
  jle    L83
  mov    -0x78(%rbp),%rdx
  mov    -0x70(%rbp),%rcx
  mov    -0x64(%rbp),%eax
  mov    %rcx,%rsi
  mov    %eax,%edi
  call   <cft1st@plt>
  movl   $0x8,-0x50(%rbp)
  jmp    L36
L42:
  mov    -0x78(%rbp),%rcx
  mov    -0x70(%rbp),%rdx
  mov    -0x50(%rbp),%esi
  mov    -0x64(%rbp),%eax
  mov    %eax,%edi
  call   <cftmdl@plt>
  shll   $0x2,-0x50(%rbp)
L36:
  mov    -0x50(%rbp),%eax
  shl    $0x2,%eax
  cmp    %eax,-0x64(%rbp)
  jg     L42
L83:
  mov    -0x50(%rbp),%eax
  shl    $0x2,%eax
  cmp    %eax,-0x64(%rbp)
  jne    L12
  movl   $0x0,-0x54(%rbp)
  jmp    L56
L11:
  mov    -0x54(%rbp),%edx
  mov    -0x50(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x4c(%rbp)
  mov    -0x4c(%rbp),%edx
  mov    -0x50(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x48(%rbp)
  mov    -0x48(%rbp),%edx
  mov    -0x50(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x44(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x40(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x38(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x30(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x28(%rbp)
  mov    -0x48(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x44(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x20(%rbp)
  mov    -0x48(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x44(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x18(%rbp)
  mov    -0x48(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x44(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x10(%rbp)
  mov    -0x48(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x44(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x40(%rbp),%xmm0
  addsd  -0x20(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x38(%rbp),%xmm0
  addsd  -0x18(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x48(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x40(%rbp),%xmm0
  subsd  -0x20(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x48(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x38(%rbp),%xmm0
  subsd  -0x18(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x30(%rbp),%xmm0
  subsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x28(%rbp),%xmm0
  addsd  -0x10(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x44(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x30(%rbp),%xmm0
  addsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x44(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x28(%rbp),%xmm0
  subsd  -0x10(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  addl   $0x2,-0x54(%rbp)
L56:
  mov    -0x54(%rbp),%eax
  cmp    -0x50(%rbp),%eax
  jl     L11
  jmp    L25
L12:
  movl   $0x0,-0x54(%rbp)
  jmp    L10
L64:
  mov    -0x54(%rbp),%edx
  mov    -0x50(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x4c(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x40(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x38(%rbp)
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x54(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  addsd  %xmm1,%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x54(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  addsd  %xmm1,%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x4c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x40(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x4c(%rbp),%eax
  cltq
  add    $0x1,%rax
  lea    0x0(,%rax,8),%rdx
  mov    -0x70(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x38(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  addl   $0x2,-0x54(%rbp)
L10:
  mov    -0x54(%rbp),%eax
  cmp    -0x50(%rbp),%eax
  jl     L64
L25:
  nop
  leave
  ret
```

assistant: ```c
void cftfsub(int n, double *a, double *w) {
  int j, j1, j2, j3, l;
  double x0r, x0i, x1r, x1i, x2r, x2i, x3r, x3i;
  l = 2;
  if (n > 8) {
    cft1st(n, a, w);
    l = 8;
    while ((l << 2) < n) {
      cftmdl(n, l, a, w);
      l <<= 2;
    }
  }
  if ((l << 2) == n) {
    for (j = 0; j < l; j += 2) {
      j1 = j + l;
      j2 = j1 + l;
      j3 = j2 + l;
      x0r = a[j] + a[j1];
      x0i = a[j + 1] + a[j1 + 1];
      x1r = a[j] - a[j1];
      x1i = a[j + 1] - a[j1 + 1];
      x2r = a[j2] + a[j3];
      x2i = a[j2 + 1] + a[j3 + 1];
      x3r = a[j2] - a[j3];
      x3i = a[j2 + 1] - a[j3 + 1];
      a[j] = x0r + x2r;
      a[j + 1] = x0i + x2i;
      a[j2] = x0r - x2r;
      a[j2 + 1] = x0i - x2i;
      a[j1] = x1r - x3i;
      a[j1 + 1] = x1i + x3r;
      a[j3] = x1r + x3i;
      a[j3 + 1] = x1i - x3r;
    }
  } else {
    for (j = 0; j < l; j += 2) {
      j1 = j + l;
      x0r = a[j] - a[j1];
      x0i = a[j + 1] - a[j1 + 1];
      a[j] += a[j1];
      a[j + 1] += a[j1 + 1];
      a[j1] = x0r;
      a[j1 + 1] = x0i;
    }
  }
}
```