user: Please show me the C implementation that matches the assembly code listed below:

```asm
<flip_C4>:
  endbr64
  movabs $0x400000000000,%rax
  mov    %rdi,%rdx
  push   %r13
  movabs $0x2000000000,%r13
  shr    $0x9,%rdx
  push   %r12
  mov    %rdi,%r12
  and    %rsi,%rdx
  shr    %r12
  push   %rbp
  mov    %rdi,%rbp
  and    %rax,%rdx
  mov    %rdi,%rax
  and    %rsi,%r12
  and    $0x80402,%edi
  shl    $0x7,%rax
  push   %rbx
  mov    %rsi,%rbx
  and    %rsi,%rax
  and    $0x40000000,%eax
  or     %rdx,%rax
  sub    $0x8,%rsp
  movabs $0x4000000000,%rdx
  and    %rdx,%r12
  movabs $0x1feff7f800,%rdx
  or     %rax,%r12
  mov    %rsi,%rax
  and    $0x10080400,%eax
  or     %rdx,%rax
  mov    %rdi,%rdx
  shl    $0x9,%rdx
  add    %rdx,%rax
  test   %r13,%rax
  jne    L63
L71:
  movabs $0x1fdfdfc000,%rdx
  mov    %rbp,%rdi
  mov    %rbx,%rax
  movabs $0x2000000000,%r13
  and    $0x202020,%edi
  and    $0x20202000,%eax
  or     %rdx,%rax
  mov    %rdi,%rdx
  shl    $0x8,%rdx
  add    %rdx,%rax
  test   %r13,%rax
  jne    L61
L31:
  movabs $0xf00000000,%rdi
  and    %rbp,%rdi
  lea    (%rbx,%rdi,2),%rax
  bt     $0x25,%rax
  jb     L30
L8:
  movabs $0x8100000000000,%rcx
  mov    %rbx,%rax
  movabs $0x3f7e00000000000,%rdx
  and    %rcx,%rax
  or     %rdx,%rax
  movabs $0x100000000000,%rdx
  add    %rdx,%rax
  movabs $0x408000000000000,%rdx
  and    %rbp,%rax
  and    %rdx,%rax
  je     L40
  sub    $0x1,%rax
  and    %rcx,%rax
  or     %rax,%r12
L40:
  movabs $0x20200000000000,%rdx
  movabs $0x1fdfc00000000000,%rax
  and    %rdx,%rbx
  or     %rax,%rbx
  movabs $0x200000000000,%rax
  add    %rax,%rbx
  movabs $0x2020000000000000,%rax
  and    %rbp,%rbx
  and    %rax,%rbx
  je     L22
  sub    $0x1,%rbx
  and    %rdx,%rbx
  or     %rbx,%r12
L22:
  add    $0x8,%rsp
  mov    %r12,%rax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nopl   0x0(%rax)
L63:
  call   <last_bit@plt>
  mov    $0x2,%edx
  mov    %eax,%ecx
  shl    %cl,%rdx
  sub    %rdx,%r13
  and    $0x10080400,%r13d
  or     %r13,%r12
  jmp    L71
  nopl   0x0(%rax)
L30:
  call   <last_bit@plt>
  mov    $0x2,%edx
  mov    %eax,%ecx
  movabs $0x2000000000,%rax
  shl    %cl,%rdx
  sub    %rdx,%rax
  or     %rax,%r12
  jmp    L8
  nopl   0x0(%rax)
L61:
  call   <last_bit@plt>
  mov    $0x2,%edx
  mov    %eax,%ecx
  shl    %cl,%rdx
  sub    %rdx,%r13
  and    $0x20202000,%r13d
  or     %r13,%r12
  jmp    L31
```

assistant: ```c
unsigned long long flip_C4(const unsigned long long discs_player, const unsigned long long discs_opponent) {
  unsigned long long my_discs, opp_discs, r;
  unsigned long long flipped = (discs_opponent & 0X0000400000000000ULL) & (discs_player >> 9);
  flipped |= (discs_opponent & 0X0000000040000000ULL) & (discs_player << 7);
  flipped |= (discs_opponent & 0X0000004000000000ULL) & (discs_player >> 1);
  my_discs = discs_player & 0X0000000000080402ULL;
  opp_discs = (discs_opponent & 0X0000000010080400ULL) | 0X0000001FEFF7F800ULL;
  r = ((my_discs << 9) + opp_discs) & 0X0000002000000000ULL;
  if (r != 0) {
    flipped |= (0X0000002000000000ULL - (0X2ULL << last_bit(my_discs))) & 0X0000000010080400ULL;
  }
  my_discs = discs_player & 0X0000000000202020ULL;
  opp_discs = (discs_opponent & 0X0000000020202000ULL) | 0X0000001FDFDFC000ULL;
  r = ((my_discs << 8) + opp_discs) & 0X0000002000000000ULL;
  if (r != 0) {
    flipped |= (0X0000002000000000ULL - (0X2ULL << last_bit(my_discs))) & 0X0000000020202000ULL;
  }
  my_discs = discs_player & 0X0000000F00000000ULL;
  r = ((my_discs << 1) + discs_opponent) & 0X0000002000000000ULL;
  if (r != 0) {
    flipped |= 0X0000002000000000ULL - (0X2ULL << last_bit(my_discs));
  }
  my_discs = discs_player & 0X0408000000000000ULL;
  opp_discs = (discs_opponent & 0X0008100000000000ULL) | 0X03F7E00000000000ULL;
  r = (opp_discs + 0X0000100000000000ULL) & my_discs;
  if (r != 0) {
    flipped |= (r - 1) & 0X0008100000000000ULL;
  }
  my_discs = discs_player & 0X2020000000000000ULL;
  opp_discs = (discs_opponent & 0X0020200000000000ULL) | 0X1FDFC00000000000ULL;
  r = (opp_discs + 0X0000200000000000ULL) & my_discs;
  if (r != 0) {
    flipped |= (r - 1) & 0X0020200000000000ULL;
  }
  return flipped;
}
```