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

```asm
<flip_B4>:
  endbr64
  push   %r13
  movabs $0x4000000000,%r13
  push   %r12
  push   %rbp
  mov    %rdi,%rbp
  movabs $0x1f00000000,%rdi
  push   %rbx
  and    %rbp,%rdi
  mov    %rsi,%rbx
  lea    (%rsi,%rdi,2),%r12
  sub    $0x8,%rsp
  and    %r13,%r12
  jne    L49
L69:
  movabs $0x10200000000000,%rcx
  mov    %rbx,%rax
  movabs $0x7efc00000000000,%rdx
  and    %rcx,%rax
  or     %rdx,%rax
  movabs $0x200000000000,%rdx
  add    %rdx,%rax
  movabs $0x810000000000000,%rdx
  and    %rbp,%rax
  and    %rdx,%rax
  je     L58
  sub    $0x1,%rax
  and    %rcx,%rax
  or     %rax,%r12
L58:
  movabs $0x3fdfeff000,%rdx
  mov    %rbp,%rdi
  mov    %rbx,%rax
  movabs $0x4000000000,%r13
  and    $0x100804,%edi
  and    $0x20100800,%eax
  or     %rdx,%rax
  mov    %rdi,%rdx
  shl    $0x9,%rdx
  add    %rdx,%rax
  test   %r13,%rax
  jne    L35
L26:
  movabs $0x40400000000000,%rcx
  mov    %rbx,%rax
  movabs $0x3fbf800000000000,%rdx
  and    %rcx,%rax
  or     %rdx,%rax
  movabs $0x400000000000,%rdx
  add    %rdx,%rax
  movabs $0x4040000000000000,%rdx
  and    %rbp,%rax
  and    %rdx,%rax
  je     L30
  sub    $0x1,%rax
  and    %rcx,%rax
  or     %rax,%r12
L30:
  movabs $0x3fbfbf8000,%rax
  and    $0x404040,%ebp
  and    $0x40404000,%ebx
  movabs $0x4000000000,%r13
  or     %rax,%rbx
  mov    %rbp,%rax
  shl    $0x8,%rax
  add    %rax,%rbx
  test   %r13,%rbx
  jne    L43
  add    $0x8,%rsp
  mov    %r12,%rax
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
  nop
L49:
  call   <last_bit@plt>
  mov    $0x2,%edx
  mov    %r13,%r12
  mov    %eax,%ecx
  shl    %cl,%rdx
  sub    %rdx,%r12
  jmp    L69
  nopw   0x0(%rax,%rax,1)
L43:
  mov    %rbp,%rdi
  call   <last_bit@plt>
  mov    $0x2,%edx
  add    $0x8,%rsp
  mov    %eax,%ecx
  pop    %rbx
  pop    %rbp
  shl    %cl,%rdx
  sub    %rdx,%r13
  and    $0x40404000,%r13d
  or     %r13,%r12
  mov    %r12,%rax
  pop    %r12
  pop    %r13
  ret
  nopl   (%rax)
L35:
  call   <last_bit@plt>
  mov    $0x2,%edx
  mov    %eax,%ecx
  shl    %cl,%rdx
  sub    %rdx,%r13
  and    $0x20100800,%r13d
  or     %r13,%r12
  jmp    L26
```

assistant: ```c
unsigned long long flip_B4(const unsigned long long discs_player, const unsigned long long discs_opponent) {
  unsigned long long my_discs, opp_discs, r, flipped = 0ULL;
  my_discs = discs_player & 0X0000001F00000000ULL;
  r = ((my_discs << 1) + discs_opponent) & 0X0000004000000000ULL;
  if (r != 0) {
    flipped |= 0X0000004000000000ULL - (0X2ULL << last_bit(my_discs));
  }
  my_discs = discs_player & 0X0810000000000000ULL;
  opp_discs = (discs_opponent & 0X0010200000000000ULL) | 0X07EFC00000000000ULL;
  r = (opp_discs + 0X0000200000000000ULL) & my_discs;
  if (r != 0) {
    flipped |= (r - 1) & 0X0010200000000000ULL;
  }
  my_discs = discs_player & 0X0000000000100804ULL;
  opp_discs = (discs_opponent & 0X0000000020100800ULL) | 0X0000003FDFEFF000ULL;
  r = ((my_discs << 9) + opp_discs) & 0X0000004000000000ULL;
  if (r != 0) {
    flipped |= (0X0000004000000000ULL - (0X2ULL << last_bit(my_discs))) & 0X0000000020100800ULL;
  }
  my_discs = discs_player & 0X4040000000000000ULL;
  opp_discs = (discs_opponent & 0X0040400000000000ULL) | 0X3FBF800000000000ULL;
  r = (opp_discs + 0X0000400000000000ULL) & my_discs;
  if (r != 0) {
    flipped |= (r - 1) & 0X0040400000000000ULL;
  }
  my_discs = discs_player & 0X0000000000404040ULL;
  opp_discs = (discs_opponent & 0X0000000040404000ULL) | 0X0000003FBFBF8000ULL;
  r = ((my_discs << 8) + opp_discs) & 0X0000004000000000ULL;
  if (r != 0) {
    flipped |= (0X0000004000000000ULL - (0X2ULL << last_bit(my_discs))) & 0X0000000040404000ULL;
  }
  return flipped;
}
```