user: 提供的汇编代码用C语言表示会是什么样子:

```asm
<decode_alpha_block_DXT5>:
  endbr64
  push   %r15
  push   %r14
  push   %r13
  push   %r12
  push   %rbp
  push   %rbx
  mov    %rdi,%rbp
  mov    %edx,%r11d
  mov    %ecx,%edi
  mov    %ecx,-0x8(%rsp)
  mov    %r8d,-0x4(%rsp)
  movzbl (%rsi),%r10d
  movzbl 0x1(%rsi),%ebx
  movzbl 0x2(%rsi),%edx
  shl    $0x10,%rdx
  movzbl %bl,%ecx
  shl    $0x8,%rcx
  or     %rcx,%rdx
  movzbl %r10b,%ecx
  or     %rcx,%rdx
  movzbl 0x3(%rsi),%ecx
  shl    $0x18,%rcx
  or     %rcx,%rdx
  movzbl 0x4(%rsi),%ecx
  shl    $0x20,%rcx
  or     %rcx,%rdx
  movzbl 0x5(%rsi),%ecx
  shl    $0x28,%rcx
  or     %rcx,%rdx
  movzbl 0x6(%rsi),%ecx
  shl    $0x30,%rcx
  or     %rcx,%rdx
  movzbl 0x7(%rsi),%eax
  shl    $0x38,%rax
  or     %rax,%rdx
  shr    $0x10,%rdx
  test   %edi,%edi
  jle    L27
  mov    $0x4,%eax
  sub    %r11d,%eax
  lea    (%rax,%rax,2),%ecx
  movslq %r9d,%rax
  mov    %rax,-0x10(%rsp)
  mov    $0x0,%r12d
  movzbl %r10b,%r15d
  movzbl %bl,%r14d
  jmp    L43
L47:
  cmp    $0x5,%esi
  jle    L75
  cmp    $0x6,%esi
  setne  %al
  neg    %eax
L22:
  mov    %al,(%rdi)
  shr    $0x3,%rdx
  add    %r9,%rdi
  add    $0x1,%r8d
  cmp    %r8d,%r11d
  je     L38
L34:
  mov    %r10d,%eax
  mov    %edx,%esi
  and    $0x7,%esi
  je     L22
  mov    %ebx,%eax
  cmp    $0x1,%esi
  je     L22
  cmp    %bl,%r10b
  jbe    L47
  mov    %r13d,%eax
  sub    %esi,%eax
  imul   %r15d,%eax
  sub    $0x1,%esi
  imul   %r14d,%esi
  add    %eax,%esi
  movslq %esi,%rax
  imul   $0xffffffff92492493,%rax,%rax
  shr    $0x20,%rax
  add    %esi,%eax
  sar    $0x2,%eax
  sar    $0x1f,%esi
  sub    %esi,%eax
  jmp    L22
L75:
  mov    $0x6,%eax
  sub    %esi,%eax
  imul   %r15d,%eax
  sub    $0x1,%esi
  imul   %r14d,%esi
  add    %eax,%esi
  movslq %esi,%rax
  imul   $0x66666667,%rax,%rax
  sar    $0x21,%rax
  sar    $0x1f,%esi
  sub    %esi,%eax
  jmp    L22
L38:
  mov    %rdx,%rax
  shr    %cl,%rax
  cmp    $0x4,%r11d
  cmovl  %rax,%rdx
  add    $0x1,%r12d
  add    -0x10(%rsp),%rbp
  cmp    %r12d,-0x8(%rsp)
  je     L27
L43:
  mov    %rbp,%rdi
  test   %r11d,%r11d
  jle    L38
  mov    $0x0,%r8d
  mov    $0x8,%r13d
  movslq -0x4(%rsp),%r9
  jmp    L34
L27:
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  pop    %r14
  pop    %r15
  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));
  }
}
```