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

```asm
<ibfR2>:
  endbr64
  mov    %edx,%r8d
  mov    %esi,%ecx
  mov    $0x1,%edx
  shl    %cl,%edx
  test   %edx,%edx
  lea    0x3(%rdx),%eax
  cmovns %edx,%eax
  sar    $0x2,%eax
  cltd
  idiv   %r8d
  add    %r8d,%r8d
  shl    $0x2,%r8
  lea    (%rdi,%r8,1),%rdx
  lea    (%rdx,%r8,1),%rcx
  lea    (%rcx,%r8,1),%rsi
  test   %eax,%eax
  je     L18
  mov    %r8d,%r8d
  shl    $0x2,%r8
  nopl   0x0(%rax)
L16:
  movss  (%rdi),%xmm3
  movss  (%rdx),%xmm7
  movss  0x4(%rdi),%xmm2
  movss  0x4(%rdx),%xmm6
  movaps %xmm3,%xmm8
  movss  (%rsi),%xmm5
  movss  (%rcx),%xmm1
  subss  %xmm7,%xmm3
  addss  %xmm7,%xmm8
  movss  0x4(%rsi),%xmm4
  movss  0x4(%rcx),%xmm0
  movss  %xmm8,(%rdi)
  movaps %xmm2,%xmm8
  subss  %xmm6,%xmm2
  addss  %xmm6,%xmm8
  movss  %xmm8,0x4(%rdi)
  movss  %xmm2,0x4(%rdx)
  movaps %xmm1,%xmm2
  subss  %xmm5,%xmm1
  addss  %xmm5,%xmm2
  movss  %xmm3,(%rdx)
  movss  %xmm2,(%rcx)
  movaps %xmm0,%xmm2
  subss  %xmm4,%xmm0
  addss  %xmm4,%xmm2
  movss  %xmm2,0x4(%rcx)
  movss  0xc(%rsi),%xmm5
  movss  0x8(%rsi),%xmm4
  movss  %xmm1,(%rsi)
  movss  %xmm0,0x4(%rsi)
  movss  0x8(%rdi),%xmm3
  movss  0xc(%rdx),%xmm7
  movss  0xc(%rdi),%xmm2
  movss  0x8(%rdx),%xmm6
  movaps %xmm3,%xmm8
  movss  0x8(%rcx),%xmm1
  movss  0xc(%rcx),%xmm0
  addss  %xmm7,%xmm3
  subss  %xmm7,%xmm8
  movss  %xmm8,0x8(%rdi)
  movaps %xmm2,%xmm8
  subss  %xmm6,%xmm2
  addss  %xmm6,%xmm8
  movss  %xmm8,0xc(%rdi)
  add    %r8,%rdi
  movss  %xmm2,0xc(%rdx)
  movaps %xmm1,%xmm2
  addss  %xmm5,%xmm1
  subss  %xmm5,%xmm2
  movss  %xmm3,0x8(%rdx)
  add    %r8,%rdx
  movss  %xmm2,0x8(%rcx)
  movaps %xmm0,%xmm2
  subss  %xmm4,%xmm0
  addss  %xmm4,%xmm2
  movss  %xmm2,0xc(%rcx)
  add    %r8,%rcx
  movss  %xmm1,0x8(%rsi)
  movss  %xmm0,0xc(%rsi)
  add    %r8,%rsi
  sub    $0x1,%eax
  jne    L16
L18:
  ret
```

assistant: ```c
void ibfR2(float *ioptr, int M, int NDiffU) {
  unsigned int pos;
  unsigned int posi;
  unsigned int pinc;
  unsigned int pnext;
  unsigned int NSameU;
  unsigned int SameUCnt;
  float *pstrt;
  float *p0r, *p1r, *p2r, *p3r;
  float f0r, f0i, f1r, f1i, f2r, f2i, f3r, f3i;
  float f4r, f4i, f5r, f5i, f6r, f6i, f7r, f7i;
  pinc = NDiffU * 2;
  pnext = pinc * 4;
  pos = 2;
  posi = pos + 1;
  NSameU = ((uint32_t)1 << (M)) / 4 / NDiffU;
  pstrt = ioptr;
  p0r = pstrt;
  p1r = pstrt + pinc;
  p2r = p1r + pinc;
  p3r = p2r + pinc;
  for (SameUCnt = NSameU; SameUCnt > 0; SameUCnt--) {
    f0r = *p0r;
    f1r = *p1r;
    f0i = *(p0r + 1);
    f1i = *(p1r + 1);
    f2r = *p2r;
    f3r = *p3r;
    f2i = *(p2r + 1);
    f3i = *(p3r + 1);
    f4r = f0r + f1r;
    f4i = f0i + f1i;
    f5r = f0r - f1r;
    f5i = f0i - f1i;
    f6r = f2r + f3r;
    f6i = f2i + f3i;
    f7r = f2r - f3r;
    f7i = f2i - f3i;
    *p0r = f4r;
    *(p0r + 1) = f4i;
    *p1r = f5r;
    *(p1r + 1) = f5i;
    *p2r = f6r;
    *(p2r + 1) = f6i;
    *p3r = f7r;
    *(p3r + 1) = f7i;
    f0r = *(p0r + pos);
    f1i = *(p1r + posi);
    f0i = *(p0r + posi);
    f1r = *(p1r + pos);
    f2r = *(p2r + pos);
    f3i = *(p3r + posi);
    f2i = *(p2r + posi);
    f3r = *(p3r + pos);
    f4r = f0r - f1i;
    f4i = f0i + f1r;
    f5r = f0r + f1i;
    f5i = f0i - f1r;
    f6r = f2r - f3i;
    f6i = f2i + f3r;
    f7r = f2r + f3i;
    f7i = f2i - f3r;
    *(p0r + pos) = f4r;
    *(p0r + posi) = f4i;
    *(p1r + pos) = f5r;
    *(p1r + posi) = f5i;
    *(p2r + pos) = f6r;
    *(p2r + posi) = f6i;
    *(p3r + pos) = f7r;
    *(p3r + posi) = f7i;
    p0r += pnext;
    p1r += pnext;
    p2r += pnext;
    p3r += pnext;
  }
}
```