user: What is the c source code of the assembly code below:

```asm
<v4lconvert_spca508_to_yuv420>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x28(%rbp)
  mov    %rsi,-0x30(%rbp)
  mov    %edx,-0x34(%rbp)
  mov    %ecx,-0x38(%rbp)
  mov    %r8d,-0x3c(%rbp)
  mov    -0x28(%rbp),%rax
  mov    %rax,-0x10(%rbp)
  movl   $0x0,-0x18(%rbp)
  jmp    L18
L76:
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
  movl   $0x0,-0x14(%rbp)
  jmp    L103
L119:
  mov    -0x10(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x10(%rbp)
  mov    (%rax),%rdx
  mov    -0x8(%rbp),%rax
  mov    %rdx,(%rax)
  mov    -0x8(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x8(%rbp)
  mov    (%rax),%rdx
  movabs $0x8080808080808080,%rcx
  xor    %rcx,%rdx
  mov    %rdx,(%rax)
  mov    -0x14(%rbp),%eax
  add    $0x8,%eax
  mov    %eax,-0x14(%rbp)
L103:
  mov    -0x14(%rbp),%eax
  cmp    -0x34(%rbp),%eax
  jl     L119
  cmpl   $0x0,-0x3c(%rbp)
  je     L67
  mov    -0x34(%rbp),%eax
  imul   -0x38(%rbp),%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  movslq %eax,%rcx
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  cltq
  lea    (%rcx,%rax,1),%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
  jmp    L102
L67:
  mov    -0x34(%rbp),%eax
  imul   -0x38(%rbp),%eax
  movslq %eax,%rcx
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  cltq
  lea    (%rcx,%rax,1),%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
L102:
  movl   $0x0,-0x14(%rbp)
  jmp    L86
L130:
  mov    -0x10(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x10(%rbp)
  mov    (%rax),%rdx
  mov    -0x8(%rbp),%rax
  mov    %rdx,(%rax)
  mov    -0x8(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x8(%rbp)
  mov    (%rax),%rdx
  movabs $0x8080808080808080,%rcx
  xor    %rcx,%rdx
  mov    %rdx,(%rax)
  mov    -0x14(%rbp),%eax
  add    $0x8,%eax
  mov    %eax,-0x14(%rbp)
L86:
  mov    -0x34(%rbp),%eax
  mov    %eax,%edx
  shr    $0x1f,%edx
  add    %edx,%eax
  sar    %eax
  cmp    %eax,-0x14(%rbp)
  jl     L130
  cmpl   $0x0,-0x3c(%rbp)
  je     L99
  mov    -0x34(%rbp),%eax
  imul   -0x38(%rbp),%eax
  movslq %eax,%rcx
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  cltq
  lea    (%rcx,%rax,1),%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
  jmp    L7
L99:
  mov    -0x34(%rbp),%eax
  imul   -0x38(%rbp),%eax
  mov    %eax,%edx
  mov    %edx,%eax
  shl    $0x2,%eax
  add    %edx,%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  movslq %eax,%rcx
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  lea    0x3(%rax),%edx
  test   %eax,%eax
  cmovs  %edx,%eax
  sar    $0x2,%eax
  cltq
  lea    (%rcx,%rax,1),%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
L7:
  movl   $0x0,-0x14(%rbp)
  jmp    L26
L74:
  mov    -0x10(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x10(%rbp)
  mov    (%rax),%rdx
  mov    -0x8(%rbp),%rax
  mov    %rdx,(%rax)
  mov    -0x8(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x8(%rbp)
  mov    (%rax),%rdx
  movabs $0x8080808080808080,%rcx
  xor    %rcx,%rdx
  mov    %rdx,(%rax)
  mov    -0x14(%rbp),%eax
  add    $0x8,%eax
  mov    %eax,-0x14(%rbp)
L26:
  mov    -0x34(%rbp),%eax
  mov    %eax,%edx
  shr    $0x1f,%edx
  add    %edx,%eax
  sar    %eax
  cmp    %eax,-0x14(%rbp)
  jl     L74
  mov    -0x18(%rbp),%eax
  imul   -0x34(%rbp),%eax
  movslq %eax,%rdx
  mov    -0x34(%rbp),%eax
  cltq
  add    %rax,%rdx
  mov    -0x30(%rbp),%rax
  add    %rdx,%rax
  mov    %rax,-0x8(%rbp)
  movl   $0x0,-0x14(%rbp)
  jmp    L68
L28:
  mov    -0x10(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x10(%rbp)
  mov    (%rax),%rdx
  mov    -0x8(%rbp),%rax
  mov    %rdx,(%rax)
  mov    -0x8(%rbp),%rax
  lea    0x8(%rax),%rdx
  mov    %rdx,-0x8(%rbp)
  mov    (%rax),%rdx
  movabs $0x8080808080808080,%rcx
  xor    %rcx,%rdx
  mov    %rdx,(%rax)
  mov    -0x14(%rbp),%eax
  add    $0x8,%eax
  mov    %eax,-0x14(%rbp)
L68:
  mov    -0x14(%rbp),%eax
  cmp    -0x34(%rbp),%eax
  jl     L28
  addl   $0x2,-0x18(%rbp)
L18:
  mov    -0x18(%rbp),%eax
  cmp    -0x38(%rbp),%eax
  jl     L76
  nop
  nop
  pop    %rbp
  ret
```

assistant: ```c
void v4lconvert_spca508_to_yuv420(const unsigned char *src, unsigned char *dst, int width, int height, int yvu) {
  int i, j;
  unsigned long *lsrc = (unsigned long *)src;
  for (i = 0; i < height; i += 2) {
    unsigned long *ldst = (unsigned long *)(dst + i * width);
    for (j = 0; j < width; j += sizeof(long)) {
      *ldst = *lsrc++;
      *ldst++ ^= 0x8080808080808080ULL;
    }
    if (yvu)
      ldst = (unsigned long *)(dst + (width * height * 5) / 4 + i * width / 4);
    else
      ldst = (unsigned long *)(dst + width * height + i * width / 4);
    for (j = 0; j < width / 2; j += sizeof(long)) {
      *ldst = *lsrc++;
      *ldst++ ^= 0x8080808080808080ULL;
    }
    if (yvu)
      ldst = (unsigned long *)(dst + width * height + i * width / 4);
    else
      ldst = (unsigned long *)(dst + (width * height * 5) / 4 + i * width / 4);
    for (j = 0; j < width / 2; j += sizeof(long)) {
      *ldst = *lsrc++;
      *ldst++ ^= 0x8080808080808080ULL;
    }
    ldst = (unsigned long *)(dst + i * width + width);
    for (j = 0; j < width; j += sizeof(long)) {
      *ldst = *lsrc++;
      *ldst++ ^= 0x8080808080808080ULL;
    }
  }
}
```