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

```asm
<vpx_post_proc_down_and_across_mb_row_c>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  sub    $0x98,%rsp
  mov    %edx,%eax
  mov    %ecx,0x48(%rsp)
  mov    %r8d,0x4c(%rsp)
  mov    %fs:0x28,%rdx
  mov    %rdx,0x88(%rsp)
  xor    %edx,%edx
  cmpl   $0x0,0xd0(%rsp)
  jle    L121
  mov    %rsi,%r12
  mov    %r9,%r15
  lea    (%rax,%rax,1),%ecx
  movslq %eax,%rdx
  mov    %rdx,0x68(%rsp)
  lea    (%rdi,%rdx,1),%rsi
  mov    %rsi,0x28(%rsp)
  mov    %ecx,%edx
  neg    %edx
  movslq %edx,%rdx
  lea    (%rdi,%rdx,1),%rsi
  mov    %rsi,0x20(%rsp)
  neg    %eax
  cltq
  add    %rdi,%rax
  mov    %rax,0x30(%rsp)
  movslq %ecx,%rax
  mov    %rax,0x70(%rsp)
  add    %rax,%rdi
  mov    %rdi,0x38(%rsp)
  test   %r8d,%r8d
  mov    $0x0,%eax
  cmovns %r8d,%eax
  lea    -0x2(%rax),%edx
  and    $0x3,%edx
  mov    %edx,0x58(%rsp)
  movslq %eax,%rdx
  lea    -0x2(%rdx),%rsi
  mov    %rsi,0x50(%rsp)
  sub    $0x1,%eax
  and    $0x3,%eax
  mov    %eax,0x5c(%rsp)
  lea    -0x1(%rdx),%rax
  mov    %rax,0x60(%rsp)
  movl   $0x0,0x44(%rsp)
  movslq %r8d,%rax
  mov    %rax,0x78(%rsp)
  mov    %r12,0x18(%rsp)
  jmp    L69
L103:
  mov    0x18(%rsp),%rax
  mov    %bpl,(%rax,%rbx,1)
  add    $0x1,%rbx
  cmp    0x8(%rsp),%rbx
  je     L120
L113:
  mov    0x20(%rsp),%rax
  movzbl (%rax,%rbx,1),%r12d
  mov    0x30(%rsp),%rax
  movzbl (%rax,%rbx,1),%r13d
  mov    0x28(%rsp),%rax
  movzbl (%rax,%rbx,1),%eax
  mov    %al,0x14(%rsp)
  mov    0x38(%rsp),%rax
  movzbl (%rax,%rbx,1),%eax
  mov    %al,0x43(%rsp)
  movzbl (%r14,%rbx,1),%ebp
  mov    %ebp,%edi
  sub    %r12d,%edi
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L103
  mov    %ebp,%edi
  sub    %r13d,%edi
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L103
  mov    %ebp,%edi
  sub    0x14(%rsp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L103
  mov    %ebp,%edi
  sub    0x43(%rsp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L103
  movzbl %r12b,%r12d
  movzbl %r13b,%r13d
  lea    0x1(%r12,%r13,1),%edx
  sar    %edx
  movzbl 0x43(%rsp),%ecx
  movzbl 0x14(%rsp),%eax
  lea    0x1(%rcx,%rax,1),%eax
  sar    %eax
  lea    0x1(%rdx,%rax,1),%eax
  sar    %eax
  movzbl %bpl,%ebp
  lea    0x1(%rax,%rbp,1),%ebp
  sar    %ebp
  jmp    L103
L19:
  and    $0x3,%r12d
  mov    %r13b,0x84(%rsp,%r12,1)
  cmp    $0x1,%ebx
  jle    L124
  mov    0x14(%rsp),%eax
  sub    $0x2,%eax
  and    $0x3,%eax
  movzbl 0x84(%rsp,%rax,1),%eax
  mov    %al,-0x2(%r14)
L124:
  add    $0x1,%rbx
  add    $0x1,%rbp
  cmp    0x8(%rsp),%rbx
  je     L0
L141:
  mov    %ebx,0x14(%rsp)
  mov    %ebx,%r12d
  mov    %rbp,%r14
  movzbl 0x0(%rbp),%r13d
  mov    %r13d,%edi
  sub    -0x2(%rbp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L19
  mov    %r13d,%edi
  sub    -0x1(%rbp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L19
  mov    %r13d,%edi
  sub    0x1(%rbp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L19
  mov    %r13d,%edi
  sub    0x2(%rbp),%dil
  movzbl %dil,%edi
  call   <abs@plt>
  cmp    (%r15,%rbx,1),%al
  jae    L19
  movzbl -0x2(%rbp),%edx
  movzbl -0x1(%rbp),%eax
  lea    0x1(%rdx,%rax,1),%edx
  sar    %edx
  movzbl 0x2(%rbp),%ecx
  movzbl 0x1(%rbp),%eax
  lea    0x1(%rcx,%rax,1),%eax
  sar    %eax
  lea    0x1(%rdx,%rax,1),%eax
  sar    %eax
  movzbl %r13b,%r13d
  lea    0x1(%rax,%r13,1),%r13d
  sar    %r13d
  jmp    L19
L0:
  movslq 0x58(%rsp),%rax
  movzbl 0x84(%rsp,%rax,1),%eax
  mov    0x18(%rsp),%rcx
  mov    0x50(%rsp),%rdx
  mov    %al,(%rcx,%rdx,1)
  movslq 0x5c(%rsp),%rax
  movzbl 0x84(%rsp,%rax,1),%eax
  mov    0x60(%rsp),%rdx
  mov    %al,(%rcx,%rdx,1)
  movslq 0x48(%rsp),%rax
  add    %rax,%rcx
  mov    %rcx,0x18(%rsp)
  addl   $0x1,0x44(%rsp)
  mov    0x44(%rsp),%edx
  mov    0x68(%rsp),%rax
  add    %rax,0x28(%rsp)
  add    %rax,0x20(%rsp)
  add    %rax,0x30(%rsp)
  add    %rax,0x38(%rsp)
  cmp    %edx,0xd0(%rsp)
  je     L121
L69:
  mov    0x20(%rsp),%r14
  add    0x70(%rsp),%r14
  mov    0x4c(%rsp),%eax
  mov    %eax,%edx
  mov    %rdx,0x8(%rsp)
  mov    $0x0,%ebx
  test   %eax,%eax
  jg     L113
  mov    0x18(%rsp),%rcx
  movzbl (%rcx),%eax
  mov    %al,-0x1(%rcx)
  mov    %al,-0x2(%rcx)
  mov    0x78(%rsp),%rsi
  movzbl -0x1(%rcx,%rsi,1),%eax
  mov    %al,0x1(%rcx,%rsi,1)
  mov    %al,(%rcx,%rsi,1)
  jmp    L0
L120:
  mov    0x18(%rsp),%rsi
  movzbl (%rsi),%eax
  mov    %al,-0x1(%rsi)
  mov    %al,-0x2(%rsi)
  mov    0x78(%rsp),%rdx
  movzbl -0x1(%rsi,%rdx,1),%eax
  mov    %al,0x1(%rsi,%rdx,1)
  mov    %al,(%rsi,%rdx,1)
  mov    %rsi,%rbp
  mov    $0x0,%ebx
  jmp    L141
L121:
  mov    0x88(%rsp),%rax
  sub    %fs:0x28,%rax
  jne    L58
  add    $0x98,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L58:
  call   <__stack_chk_fail@plt>
```

assistant: ```c
void vpx_post_proc_down_and_across_mb_row_c(unsigned char *src_ptr, unsigned char *dst_ptr, int src_pixels_per_line, int dst_pixels_per_line, int cols, unsigned char *f, int size) {
  unsigned char *p_src, *p_dst;
  int row;
  int col;
  unsigned char v;
  unsigned char d[4];
  for (row = 0; row < size; row++) {
    p_src = src_ptr;
    p_dst = dst_ptr;
    for (col = 0; col < cols; col++) {
      unsigned char p_above2 = p_src[col - 2 * src_pixels_per_line];
      unsigned char p_above1 = p_src[col - src_pixels_per_line];
      unsigned char p_below1 = p_src[col + src_pixels_per_line];
      unsigned char p_below2 = p_src[col + 2 * src_pixels_per_line];
      v = p_src[col];
      if ((abs(v - p_above2) < f[col]) && (abs(v - p_above1) < f[col]) && (abs(v - p_below1) < f[col]) && (abs(v - p_below2) < f[col])) {
        unsigned char k1, k2, k3;
        k1 = (p_above2 + p_above1 + 1) >> 1;
        k2 = (p_below2 + p_below1 + 1) >> 1;
        k3 = (k1 + k2 + 1) >> 1;
        v = (k3 + v + 1) >> 1;
      }
      p_dst[col] = v;
    }
    p_src = dst_ptr;
    p_dst = dst_ptr;
    p_src[-2] = p_src[-1] = p_src[0];
    p_src[cols] = p_src[cols + 1] = p_src[cols - 1];
    for (col = 0; col < cols; col++) {
      v = p_src[col];
      if ((abs(v - p_src[col - 2]) < f[col]) && (abs(v - p_src[col - 1]) < f[col]) && (abs(v - p_src[col + 1]) < f[col]) && (abs(v - p_src[col + 2]) < f[col])) {
        unsigned char k1, k2, k3;
        k1 = (p_src[col - 2] + p_src[col - 1] + 1) >> 1;
        k2 = (p_src[col + 2] + p_src[col + 1] + 1) >> 1;
        k3 = (k1 + k2 + 1) >> 1;
        v = (k3 + v + 1) >> 1;
      }
      d[col & 3] = v;
      if (col >= 2)
        p_dst[col - 2] = d[(col - 2) & 3];
    }
    p_dst[col - 2] = d[(col - 2) & 3];
    p_dst[col - 1] = d[(col - 1) & 3];
    src_ptr += src_pixels_per_line;
    dst_ptr += dst_pixels_per_line;
  }
}
```