user: Demonstrate the C code that generates the assembly output below:

```asm
<NV12toYUV420Planner>:
  endbr64
  push   %r15
  imul   %ecx,%edx
  push   %r14
  mov    %rsi,%r14
  push   %r13
  mov    %rdi,%r13
  push   %r12
  movslq %edx,%rax
  push   %rbp
  lea    0x0(,%rax,4),%r15
  push   %rbx
  lea    0x3(%rdx),%ebx
  lea    (%rsi,%r15,1),%rbp
  lea    (%rdi,%r15,1),%r12
  sub    $0x28,%rsp
  test   %edx,%edx
  cmovns %edx,%ebx
  mov    %rax,(%rsp)
  call   <memcpy@plt>
  sar    $0x2,%ebx
  lea    (%rbx,%rbx,1),%esi
  test   %esi,%esi
  jle    L4
  lea    -0x1(%rsi),%r8d
  mov    (%rsp),%rdx
  mov    %r8d,%ecx
  shr    %ecx
  lea    0x1(%rcx),%r10d
  mov    %ecx,0x1c(%rsp)
  lea    (%rdx,%r10,2),%rax
  mov    %r10,%rcx
  lea    (%r14,%rax,4),%r11
  mov    %rax,0x10(%rsp)
  movslq %ebx,%rax
  add    %rdx,%rax
  mov    %r11,0x8(%rsp)
  lea    (%rax,%r10,1),%r9
  lea    0x0(,%rax,4),%rdi
  lea    0x0(%r13,%r9,4),%r9
  lea    0x0(%r13,%rdi,1),%rdx
  cmp    %r9,%rbp
  setae  %r11b
  cmp    %rdx,0x8(%rsp)
  setbe  %r9b
  add    $0x4,%r15
  sub    %r15,%rdi
  or     %r11d,%r9d
  cmp    $0x8,%rdi
  seta   %dil
  cmp    $0x1,%r8d
  seta   %r11b
  and    %r11d,%edi
  test   %dil,%r9b
  je     L8
  mov    0x10(%rsp),%rdi
  sub    %r10,%rdi
  lea    0x0(%r13,%rdi,4),%rdi
  cmp    %rdi,%rbp
  setae  %dil
  cmp    0x8(%rsp),%r12
  setae  %r9b
  or     %r9b,%dil
  je     L8
  cmp    $0x5,%r8d
  jbe    L25
  mov    %r10d,%edi
  xor    %esi,%esi
  shr    $0x2,%edi
  shl    $0x4,%rdi
  nopl   (%rax)
L56:
  movdqu 0x0(%rbp,%rsi,2),%xmm0
  movdqu 0x10(%rbp,%rsi,2),%xmm1
  movdqa %xmm0,%xmm2
  shufps $0xdd,%xmm1,%xmm0
  shufps $0x88,%xmm1,%xmm2
  movups %xmm2,(%r12,%rsi,1)
  movups %xmm0,(%rdx,%rsi,1)
  add    $0x10,%rsi
  cmp    %rdi,%rsi
  jne    L56
  mov    %ecx,%edi
  and    $0xfffffffc,%edi
  mov    %edi,%esi
  lea    (%rdi,%rdi,1),%edx
  cmp    %edi,%ecx
  je     L4
L12:
  sub    %edi,%ecx
  cmp    %edi,0x1c(%rsp)
  je     L83
  mov    %edi,%r9d
  mov    (%rsp),%rdi
  add    %r9,%rax
  lea    (%rdi,%r9,2),%rdi
  lea    (%r14,%rdi,4),%r8
  sub    %r9,%rdi
  movq   (%r8),%xmm0
  movq   0x8(%r8),%xmm1
  movdqa %xmm0,%xmm2
  punpckldq %xmm1,%xmm0
  punpckldq %xmm1,%xmm2
  pshufd $0xe,%xmm0,%xmm0
  movq   %xmm2,0x0(%r13,%rdi,4)
  movq   %xmm0,0x0(%r13,%rax,4)
  mov    %ecx,%eax
  and    $0xfffffffe,%eax
  lea    (%rdx,%rax,2),%edx
  add    %eax,%esi
  cmp    %eax,%ecx
  je     L4
L83:
  movslq %edx,%rax
  movslq %esi,%rdx
  add    %esi,%ebx
  mov    0x0(%rbp,%rax,4),%ecx
  movslq %ebx,%rbx
  mov    %ecx,(%r12,%rdx,4)
  mov    0x4(%rbp,%rax,4),%eax
  mov    %eax,(%r12,%rbx,4)
L4:
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
  nop
L8:
  xor    %eax,%eax
  nopw   0x0(%rax,%rax,1)
L19:
  mov    0x0(%rbp,%rax,4),%ecx
  mov    %ecx,(%r12,%rax,2)
  mov    0x4(%rbp,%rax,4),%ecx
  mov    %ecx,(%rdx,%rax,2)
  add    $0x2,%rax
  cmp    %eax,%esi
  jg     L19
  add    $0x28,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L25:
  xor    %edi,%edi
  xor    %esi,%esi
  xor    %edx,%edx
  jmp    L12
```

assistant: ```c
void NV12toYUV420Planner(uint8_t *dst_buf, uint8_t *src_buf, int width, int height) {
  int luma_plane_len = (width * height);
  int single_chroma_plane_len = ((width * height) / 4);
  uint8_t *src_chroma = src_buf + luma_plane_len;
  uint8_t *dst_chroma = dst_buf + luma_plane_len;
  memcpy(dst_buf, src_buf, luma_plane_len);
  int i, j;
  for (i = 0, j = 0; i < (single_chroma_plane_len * 2); i = i + 2, j++) {
    dst_chroma[j] = src_chroma[i];
    dst_chroma[j + single_chroma_plane_len] = src_chroma[i + 1];
  }
}
```