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

```asm
<decode_alpha_block_DXT5>:
  endbr64
  mov    %rsi,%rax
  movzbl (%rsi),%esi
  movzbl 0x1(%rax),%r10d
  mov    (%rax),%rax
  shr    $0x10,%rax
  test   %ecx,%ecx
  jle    L199
  push   %r15
  mov    %edx,%r11d
  mov    $0x4,%edx
  mov    %r8d,%r15d
  push   %r14
  sub    %r11d,%edx
  push   %r13
  push   %r12
  push   %rbp
  mov    %ecx,%ebp
  push   %rbx
  lea    (%rdx,%rdx,2),%ebx
  mov    %ebx,-0xc(%rsp)
  cmp    $0x1,%r8d
  jne    L18
  lea    -0x1(%r11),%r12d
  movslq %r9d,%rbx
  movzbl %sil,%r13d
  xor    %r9d,%r9d
  lea    0x1(%rdi,%r12,1),%rdi
  nopl   0x0(%rax)
L115:
  mov    %rdi,%rdx
  sub    %r12,%rdx
  sub    $0x1,%rdx
  test   %r11d,%r11d
  jle    L108
  movzbl %r10b,%r8d
  cmp    %r10b,%sil
  ja     L37
  mov    $0x6,%r15d
  movzbl %r10b,%r14d
  cs nopw 0x0(%rax,%rax,1)
L208:
  mov    %eax,%r8d
  mov    %esi,%ecx
  and    $0x7,%r8d
  je     L81
  mov    %r10d,%ecx
  cmp    $0x1,%r8d
  je     L81
  cmp    $0x5,%r8d
  jle    L124
  cmp    $0x6,%r8d
  setne  %cl
  neg    %ecx
  nopw   0x0(%rax,%rax,1)
L81:
  mov    %cl,(%rdx)
  add    $0x1,%rdx
  shr    $0x3,%rax
  cmp    %rdi,%rdx
  jne    L208
  cmp    $0x3,%r11d
  jle    L108
L12:
  add    $0x1,%r9d
  add    %rbx,%rdi
  cmp    %r9d,%ebp
  jne    L115
L181:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  ret
L37:
  mov    %eax,%r14d
  mov    %esi,%ecx
  and    $0x7,%r14d
  je     L59
  mov    %r10d,%ecx
  cmp    $0x1,%r14d
  je     L59
  mov    $0x8,%ecx
  sub    %r14d,%ecx
  sub    $0x1,%r14d
  imul   %r13d,%ecx
  imul   %r8d,%r14d
  add    %ecx,%r14d
  mov    %r14,%rcx
  imul   $0x24924925,%r14,%r14
  shr    $0x20,%r14
  sub    %r14d,%ecx
  shr    %ecx
  add    %r14d,%ecx
  shr    $0x2,%ecx
  nopl   0x0(%rax)
L59:
  mov    %cl,(%rdx)
  add    $0x1,%rdx
  shr    $0x3,%rax
  cmp    %rdi,%rdx
  jne    L37
  cmp    $0x3,%r11d
  jg     L12
L108:
  movzbl -0xc(%rsp),%ecx
  shr    %cl,%rax
  jmp    L12
  nopw   0x0(%rax,%rax,1)
L124:
  mov    %r15d,%ecx
  sub    %r8d,%ecx
  sub    $0x1,%r8d
  imul   %r14d,%r8d
  imul   %r13d,%ecx
  add    %r8d,%ecx
  mov    $0xcccccccd,%r8d
  mov    %ecx,%ecx
  imul   %r8,%rcx
  shr    $0x22,%rcx
  jmp    L81
L18:
  mov    %rdi,%rbx
  movzbl %sil,%edi
  movslq %r9d,%r14
  xor    %r12d,%r12d
  mov    %edi,-0x8(%rsp)
  mov    %rbx,%rdx
  test   %r11d,%r11d
  jle    L250
  nopw   0x0(%rax,%rax,1)
L154:
  movslq %r15d,%r8
  xor    %edi,%edi
  cmp    %r10b,%sil
  ja     L180
  movzbl %r10b,%ecx
  mov    $0x6,%r13d
  mov    %ecx,-0x4(%rsp)
  nopl   0x0(%rax)
L105:
  mov    %eax,%r9d
  mov    %esi,%ecx
  and    $0x7,%r9d
  je     L235
  mov    %r10d,%ecx
  cmp    $0x1,%r9d
  je     L235
  cmp    $0x5,%r9d
  jg     L293
  mov    %r13d,%ecx
  sub    %r9d,%ecx
  imul   -0x8(%rsp),%ecx
  sub    $0x1,%r9d
  imul   -0x4(%rsp),%r9d
  add    %r9d,%ecx
  mov    $0xcccccccd,%r9d
  mov    %ecx,%ecx
  imul   %r9,%rcx
  shr    $0x22,%rcx
  cs nopw 0x0(%rax,%rax,1)
L235:
  add    $0x1,%edi
  mov    %cl,(%rdx)
  shr    $0x3,%rax
  add    %r8,%rdx
  cmp    %edi,%r11d
  jne    L105
L211:
  cmp    $0x3,%r11d
  jle    L250
L95:
  add    $0x1,%r12d
  add    %r14,%rbx
  cmp    %r12d,%ebp
  je     L181
  mov    %rbx,%rdx
  test   %r11d,%r11d
  jg     L154
  nopl   0x0(%rax,%rax,1)
L250:
  movzbl -0xc(%rsp),%ecx
  shr    %cl,%rax
  jmp    L95
L180:
  movzbl %r10b,%r9d
  cs nopw 0x0(%rax,%rax,1)
L164:
  mov    %eax,%r13d
  mov    %esi,%ecx
  and    $0x7,%r13d
  je     L117
  mov    %r10d,%ecx
  cmp    $0x1,%r13d
  je     L117
  mov    $0x8,%ecx
  sub    %r13d,%ecx
  imul   -0x8(%rsp),%ecx
  sub    $0x1,%r13d
  imul   %r9d,%r13d
  add    %ecx,%r13d
  mov    %r13,%rcx
  imul   $0x24924925,%r13,%r13
  shr    $0x20,%r13
  sub    %r13d,%ecx
  shr    %ecx
  add    %r13d,%ecx
  shr    $0x2,%ecx
  nopl   (%rax)
L117:
  add    $0x1,%edi
  mov    %cl,(%rdx)
  shr    $0x3,%rax
  add    %r8,%rdx
  cmp    %edi,%r11d
  jne    L164
  jmp    L211
L293:
  cmp    $0x6,%r9d
  setne  %cl
  neg    %ecx
  jmp    L235
L199:
  ret
```

assistant: ```c
void decode_alpha_block_DXT5(unsigned char *dst, unsigned char *src, int w, int h, int bpp, int rowbytes) {
  int x, y, code;
  unsigned char *d;
  unsigned char a0 = src[0];
  unsigned char a1 = src[1];
  unsigned long long bits = (((unsigned long long)(src)[0]) | ((unsigned long long)(src)[1] << 8) | ((unsigned long long)(src)[2] << 16) | ((unsigned long long)(src)[3] << 24) | ((unsigned long long)(src)[4] << 32) | ((unsigned long long)(src)[5] << 40) | ((unsigned long long)(src)[6] << 48) | ((unsigned long long)(src)[7] << 56)) >> 16;
  for (y = 0; y < h; ++y) {
    d = dst + (y * rowbytes);
    for (x = 0; x < w; ++x) {
      code = ((unsigned int)bits) & 0x07;
      if (code == 0)
        d[0] = a0;
      else if (code == 1)
        d[0] = a1;
      else if (a0 > a1)
        d[0] = ((8 - code) * a0 + (code - 1) * a1) / 7;
      else if (code >= 6)
        d[0] = (code == 6) ? 0 : 255;
      else
        d[0] = ((6 - code) * a0 + (code - 1) * a1) / 5;
      bits >>= 3;
      d += bpp;
    }
    if (w < 4)
      bits >>= (3 * (4 - w));
  }
}
```