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

```asm
<fft_rec>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x70,%rsp
  mov    %edi,-0x44(%rbp)
  mov    %esi,-0x48(%rbp)
  mov    %edx,-0x4c(%rbp)
  mov    %rcx,-0x58(%rbp)
  mov    %r8,-0x60(%rbp)
  mov    %r9,-0x68(%rbp)
  mov    -0x44(%rbp),%eax
  mov    %eax,%edx
  shr    $0x1f,%edx
  add    %edx,%eax
  sar    %eax
  mov    %eax,-0x34(%rbp)
  cmpl   $0x2,-0x44(%rbp)
  je     L33
  mov    -0x4c(%rbp),%eax
  lea    (%rax,%rax,1),%edi
  mov    -0x60(%rbp),%r8
  mov    -0x68(%rbp),%rcx
  mov    -0x58(%rbp),%rdx
  mov    -0x48(%rbp),%esi
  mov    -0x34(%rbp),%eax
  mov    %r8,%r9
  mov    %rcx,%r8
  mov    %rdx,%rcx
  mov    %edi,%edx
  mov    %eax,%edi
  call   <fft_rec>
  mov    -0x4c(%rbp),%eax
  lea    (%rax,%rax,1),%edi
  mov    -0x48(%rbp),%edx
  mov    -0x4c(%rbp),%eax
  lea    (%rdx,%rax,1),%esi
  mov    -0x60(%rbp),%r8
  mov    -0x68(%rbp),%rcx
  mov    -0x58(%rbp),%rdx
  mov    -0x34(%rbp),%eax
  mov    %r8,%r9
  mov    %rcx,%r8
  mov    %rdx,%rcx
  mov    %edi,%edx
  mov    %eax,%edi
  call   <fft_rec>
  movl   $0x0,-0x38(%rbp)
  jmp    L38
L4:
  mov    -0x38(%rbp),%eax
  imul   -0x4c(%rbp),%eax
  mov    %eax,%edx
  mov    -0x48(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x30(%rbp)
  mov    -0x34(%rbp),%eax
  imul   -0x4c(%rbp),%eax
  mov    %eax,%edx
  mov    -0x30(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x2c(%rbp)
  mov    -0x38(%rbp),%eax
  imul   -0x4c(%rbp),%eax
  lea    (%rax,%rax,1),%edx
  mov    -0x48(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x28(%rbp)
  mov    -0x28(%rbp),%edx
  mov    -0x4c(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x24(%rbp)
  fildl  -0x38(%rbp)
  fldt   0xddf(%rip)        # 2000 <_fini+0xacc>
  fmulp  %st,%st(1)
  pxor   %xmm2,%xmm2
  cvtsi2sdl -0x44(%rbp),%xmm2
  movsd  %xmm2,-0x70(%rbp)
  fldl   -0x70(%rbp)
  fdivrp %st,%st(1)
  lea    -0x10(%rsp),%rsp
  fstpt  (%rsp)
  call   <cos@plt>
  add    $0x10,%rsp
  movq   %xmm0,%rax
  mov    %rax,-0x20(%rbp)
  fildl  -0x38(%rbp)
  fldt   0xda7(%rip)        # 2000 <_fini+0xacc>
  fmulp  %st,%st(1)
  pxor   %xmm3,%xmm3
  cvtsi2sdl -0x44(%rbp),%xmm3
  movsd  %xmm3,-0x70(%rbp)
  fldl   -0x70(%rbp)
  fdivrp %st,%st(1)
  lea    -0x10(%rsp),%rsp
  fstpt  (%rsp)
  call   <sin@plt>
  add    $0x10,%rsp
  movq   %xmm0,%rax
  mov    %rax,-0x18(%rbp)
  mov    -0x24(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  movapd %xmm0,%xmm1
  mulsd  -0x20(%rbp),%xmm1
  mov    -0x24(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mulsd  -0x18(%rbp),%xmm0
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x10(%rbp)
  mov    -0x24(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mulsd  -0x20(%rbp),%xmm0
  mov    -0x24(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mulsd  -0x18(%rbp),%xmm1
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  mov    -0x28(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  subsd  -0x10(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x28(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  subsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,0x8(%rax)
  mov    -0x28(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  addsd  -0x10(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x28(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x68(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  addsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,0x8(%rax)
  addl   $0x1,-0x38(%rbp)
L38:
  mov    -0x38(%rbp),%eax
  cmp    -0x34(%rbp),%eax
  jl     L4
  jmp    L20
L33:
  mov    -0x48(%rbp),%eax
  mov    %eax,-0x30(%rbp)
  mov    -0x30(%rbp),%edx
  mov    -0x4c(%rbp),%eax
  add    %edx,%eax
  mov    %eax,-0x2c(%rbp)
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  subsd  %xmm1,%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm1
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  subsd  %xmm1,%xmm0
  movsd  %xmm0,0x8(%rax)
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  addsd  %xmm1,%xmm0
  movsd  %xmm0,(%rax)
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm1
  mov    -0x2c(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x58(%rbp),%rax
  add    %rdx,%rax
  movsd  0x8(%rax),%xmm0
  mov    -0x30(%rbp),%eax
  cltq
  shl    $0x4,%rax
  mov    %rax,%rdx
  mov    -0x60(%rbp),%rax
  add    %rdx,%rax
  addsd  %xmm1,%xmm0
  movsd  %xmm0,0x8(%rax)
L20:
  nop
  leave
  ret
```

assistant: ```c
void fft_rec(int N, int offset, int delta, double (*x)[2], double (*X)[2], double (*XX)[2]) {
  int N2 = N / 2;
  int k;
  double cs, sn;
  int k00, k01, k10, k11;
  double tmp0, tmp1;
  if (N != 2) {
    fft_rec(N2, offset, 2 * delta, x, XX, X);
    fft_rec(N2, offset + delta, 2 * delta, x, XX, X);
    for (k = 0; k < N2; k++) {
      k00 = offset + k * delta;
      k01 = k00 + N2 * delta;
      k10 = offset + 2 * k * delta;
      k11 = k10 + delta;
      cs = cos((6.2831853071795864769252867665590057683943L) * k / (double)N);
      sn = sin((6.2831853071795864769252867665590057683943L) * k / (double)N);
      tmp0 = cs * XX[k11][0] + sn * XX[k11][1];
      tmp1 = cs * XX[k11][1] - sn * XX[k11][0];
      X[k01][0] = XX[k10][0] - tmp0;
      X[k01][1] = XX[k10][1] - tmp1;
      X[k00][0] = XX[k10][0] + tmp0;
      X[k00][1] = XX[k10][1] + tmp1;
    }
  } else {
    k00 = offset;
    k01 = k00 + delta;
    X[k01][0] = x[k00][0] - x[k01][0];
    X[k01][1] = x[k00][1] - x[k01][1];
    X[k00][0] = x[k00][0] + x[k01][0];
    X[k00][1] = x[k00][1] + x[k01][1];
  }
}
```