user: 请将这段汇编代码片段转换成等效的C代码:

```asm
<cftfsub>:
  endbr64
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x8,%rsp
  mov    %rsi,%rbx
  cmp    $0x8,%edi
  jg     L139
  mov    $0x2,%ebp
  je     L2
L21:
  movslq %ebp,%rax
  lea    (%rbx,%rax,4),%rax
  lea    0x4(%rbx),%rdx
  mov    $0x0,%ecx
L78:
  movss  -0x4(%rdx),%xmm0
  movss  (%rax),%xmm2
  movss  (%rdx),%xmm1
  movaps %xmm1,%xmm3
  subss  0x4(%rax),%xmm3
  movaps %xmm0,%xmm4
  addss  %xmm2,%xmm4
  movss  %xmm4,-0x4(%rdx)
  addss  0x4(%rax),%xmm1
  movss  %xmm1,(%rdx)
  subss  %xmm2,%xmm0
  movss  %xmm0,(%rax)
  movss  %xmm3,0x4(%rax)
  add    $0x2,%ecx
  add    $0x8,%rax
  add    $0x8,%rdx
  cmp    %ebp,%ecx
  jl     L78
L70:
  add    $0x8,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
L139:
  mov    %edi,%r12d
  mov    %rdx,%r13
  call   <cft1st@plt>
  cmp    $0x20,%r12d
  jle    L115
  mov    $0x8,%esi
  mov    $0x20,%ebp
  jmp    L13
L43:
  mov    %eax,%ebp
L13:
  mov    %r13,%rcx
  mov    %rbx,%rdx
  mov    %r12d,%edi
  call   <cftmdl@plt>
  lea    0x0(,%rbp,4),%eax
  mov    %ebp,%esi
  cmp    %r12d,%eax
  jl     L43
  je     L22
  test   %ebp,%ebp
  jg     L21
  jmp    L70
L22:
  test   %ebp,%ebp
  jg     L133
  jmp    L70
L2:
  mov    $0x2,%ebp
L133:
  movslq %ebp,%rax
  shl    $0x2,%rax
  lea    (%rbx,%rax,1),%rdx
  mov    %rdx,%rsi
  add    %rax,%rdx
  mov    %rdx,%rcx
  add    %rax,%rdx
  mov    $0x0,%eax
L100:
  movss  (%rbx,%rax,4),%xmm2
  movss  (%rsi),%xmm5
  movaps %xmm2,%xmm4
  addss  %xmm5,%xmm4
  movss  0x4(%rbx,%rax,4),%xmm0
  movss  0x4(%rsi),%xmm1
  movaps %xmm0,%xmm3
  addss  %xmm1,%xmm3
  subss  %xmm5,%xmm2
  movaps %xmm2,%xmm9
  subss  %xmm1,%xmm0
  movss  (%rcx),%xmm1
  movss  (%rdx),%xmm8
  movaps %xmm1,%xmm6
  addss  %xmm8,%xmm6
  movss  0x4(%rcx),%xmm2
  movss  0x4(%rdx),%xmm7
  movaps %xmm2,%xmm5
  addss  %xmm7,%xmm5
  subss  %xmm8,%xmm1
  subss  %xmm7,%xmm2
  movaps %xmm4,%xmm7
  addss  %xmm6,%xmm7
  movss  %xmm7,(%rbx,%rax,4)
  movaps %xmm3,%xmm7
  addss  %xmm5,%xmm7
  movss  %xmm7,0x4(%rbx,%rax,4)
  subss  %xmm6,%xmm4
  movss  %xmm4,(%rcx)
  subss  %xmm5,%xmm3
  movss  %xmm3,0x4(%rcx)
  movaps %xmm9,%xmm3
  subss  %xmm2,%xmm3
  movss  %xmm3,(%rsi)
  movaps %xmm0,%xmm3
  addss  %xmm1,%xmm3
  movss  %xmm3,0x4(%rsi)
  addss  %xmm9,%xmm2
  movss  %xmm2,(%rdx)
  subss  %xmm1,%xmm0
  movss  %xmm0,0x4(%rdx)
  add    $0x2,%rax
  add    $0x8,%rsi
  add    $0x8,%rcx
  add    $0x8,%rdx
  cmp    %eax,%ebp
  jg     L100
  jmp    L70
L115:
  mov    $0x8,%ebp
  jne    L21
  mov    $0x8,%ebp
  jmp    L133
```

assistant: ```c
void cftfsub(int n, float *a, float *w) {
  int j, j1, j2, j3, l;
  float 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;
    }
  }
}
```