user: What would the C source look like for the assembly code provided here:

```asm
<scale2x3>:
  endbr64
  push   %r15
  mov    %ecx,%r15d
  push   %r14
  mov    %rdx,%r14
  push   %r13
  mov    %r9d,%r13d
  push   %r12
  mov    %rdi,%r12
  xor    %edi,%edi
  push   %rbp
  push   %rbx
  mov    %esi,%ebx
  sub    $0x38,%rsp
  cmpl   $0x1,0x70(%rsp)
  mov    %r8d,0x28(%rsp)
  seta   %dil
  call   <assert@plt>
  lea    (%rbx,%rbx,1),%ecx
  mov    %ebx,%edi
  sub    $0x8,%rsp
  mov    %rcx,0x8(%rsp)
  lea    (%r12,%rdi,1),%rsi
  mov    %r14,%rax
  lea    (%r14,%r15,1),%r9
  mov    %rdi,0x10(%rsp)
  mov    %rcx,%r14
  lea    (%r12,%rcx,1),%rdx
  mov    %rax,%r8
  mov    0x80(%rsp),%edi
  add    %ebx,%r14d
  mov    %r14d,%r14d
  push   %rdi
  mov    %r12,%rdi
  push   %r13
  mov    0x40(%rsp),%ecx
  push   %rcx
  mov    %rax,%rcx
  mov    %r9,0x30(%rsp)
  mov    %rax,0x38(%rsp)
  call   <stage_scale2x3@plt>
  mov    0x90(%rsp),%ebx
  lea    (%r12,%r14,1),%rsi
  mov    %rsi,0x40(%rsp)
  sub    $0x2,%ebx
  mov    %ebx,0x4c(%rsp)
  add    $0x20,%rsp
  test   %ebx,%ebx
  mov    0x10(%rsp),%r9
  je     L1
  lea    (%r15,%r15,1),%edi
  mov    0x18(%rsp),%r12
  mov    %rsi,%rbp
  mov    %rdi,0x10(%rsp)
L19:
  mov    0x10(%rsp),%rax
  sub    $0x8,%rsp
  mov    %r12,%rcx
  mov    %rbp,%rdi
  lea    (%r12,%rax,1),%r9
  mov    0x8(%rsp),%rax
  add    %r15,%r12
  mov    %r12,%r8
  lea    (%rax,%rbp,1),%rdx
  mov    0x10(%rsp),%rax
  lea    (%rax,%rbp,1),%rsi
  mov    0x80(%rsp),%eax
  add    %r14,%rbp
  push   %rax
  push   %r13
  mov    0x40(%rsp),%eax
  push   %rax
  call   <stage_scale2x3@plt>
  add    $0x20,%rsp
  sub    $0x1,%ebx
  jne    L19
  mov    0x2c(%rsp),%eax
  mov    %r15,%rdx
  imul   %rax,%r14
  add    %r14,0x20(%rsp)
  imul   %rax,%rdx
  add    %rdx,0x18(%rsp)
  mov    0x18(%rsp),%rbx
  lea    (%rbx,%r15,1),%r9
L1:
  mov    0x20(%rsp),%rdi
  mov    (%rsp),%rdx
  sub    $0x8,%rsp
  mov    %r9,%r8
  mov    0x10(%rsp),%rsi
  mov    0x80(%rsp),%eax
  add    %rdi,%rdx
  push   %rax
  add    %rdi,%rsi
  push   %r13
  mov    0x40(%rsp),%eax
  push   %rax
  mov    0x38(%rsp),%rcx
  call   <stage_scale2x3@plt>
  add    $0x58,%rsp
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
```

assistant: ```c
void scale2x3(void *void_dst, unsigned dst_slice, const void *void_src, unsigned src_slice, unsigned pixel, unsigned width, unsigned height, unsigned opt) {
  unsigned char *dst = (unsigned char *)void_dst;
  const unsigned char *src = (const unsigned char *)void_src;
  unsigned count;
  assert(height >= 2);
  count = height;
  stage_scale2x3((dst + (0) * dst_slice), (dst + (1) * dst_slice), (dst + (2) * dst_slice), (src + (0) * src_slice), (src + (0) * src_slice), (src + (1) * src_slice), pixel, width, opt);
  dst = (dst + (3) * dst_slice);
  count -= 2;
  while (count) {
    stage_scale2x3((dst + (0) * dst_slice), (dst + (1) * dst_slice), (dst + (2) * dst_slice), (src + (0) * src_slice), (src + (1) * src_slice), (src + (2) * src_slice), pixel, width, opt);
    dst = (dst + (3) * dst_slice);
    src = (src + (1) * src_slice);
    --count;
  }
  stage_scale2x3((dst + (0) * dst_slice), (dst + (1) * dst_slice), (dst + (2) * dst_slice), (src + (0) * src_slice), (src + (1) * src_slice), (src + (1) * src_slice), pixel, width, opt);
}
```