user: Converte this assembly snippet into its equivalent C code:

```asm
<computeChecksum>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  sub    $0x70,%rsp
  mov    %rdi,-0x68(%rbp)
  mov    %esi,-0x6c(%rbp)
  mov    %fs:0x28,%rax
  mov    %rax,-0x8(%rbp)
  xor    %eax,%eax
  movq   $0x3b1f3480,-0x40(%rbp)
  movq   $0x1d8f9a40,-0x38(%rbp)
  movq   $0x2ec7cd00,-0x30(%rbp)
  movq   $0x1763e680,-0x28(%rbp)
  movq   $0x2bb1f340,-0x20(%rbp)
  movq   $0xb7a89c0,-0x18(%rbp)
  mov    -0x68(%rbp),%rax
  and    $0x3fffffc0,%eax
  mov    %rax,-0x58(%rbp)
  mov    -0x68(%rbp),%rax
  shr    $0x1f,%rax
  and    $0x1,%eax
  mov    %rax,-0x50(%rbp)
  mov    -0x68(%rbp),%rax
  shr    $0x1e,%rax
  and    $0x1,%eax
  mov    %rax,-0x48(%rbp)
  cmpl   $0x0,-0x6c(%rbp)
  je     L23
  mov    -0x20(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x48(%rbp),%rdx
  add    %rdx,%rax
  and    $0x1,%eax
  test   %rax,%rax
  je     L31
  xorq   $0x40,-0x58(%rbp)
L31:
  mov    -0x18(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x50(%rbp),%rdx
  add    %rdx,%rax
  and    $0x1,%eax
  test   %rax,%rax
  je     L23
  xorq   $0x80,-0x58(%rbp)
L23:
  mov    -0x58(%rbp),%rax
  mov    %rax,-0x60(%rbp)
  cmpq   $0x0,-0x48(%rbp)
  je     L12
  xorq   $0x3fffffc0,-0x60(%rbp)
L12:
  mov    -0x40(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x50(%rbp),%rdx
  add    %rdx,%rax
  shl    $0x5,%rax
  and    $0x20,%eax
  or     %rax,-0x60(%rbp)
  mov    -0x38(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x48(%rbp),%rdx
  add    %rdx,%rax
  shl    $0x4,%rax
  and    $0x10,%eax
  or     %rax,-0x60(%rbp)
  mov    -0x30(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x50(%rbp),%rdx
  add    %rdx,%rax
  shl    $0x3,%rax
  and    $0x8,%eax
  or     %rax,-0x60(%rbp)
  mov    -0x28(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x48(%rbp),%rdx
  add    %rdx,%rax
  shl    $0x2,%rax
  and    $0x4,%eax
  or     %rax,-0x60(%rbp)
  mov    -0x20(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x48(%rbp),%rdx
  add    %rdx,%rax
  add    %rax,%rax
  and    $0x2,%eax
  or     %rax,-0x60(%rbp)
  mov    -0x18(%rbp),%rax
  and    -0x58(%rbp),%rax
  mov    %rax,%rdi
  call   <countBits@plt>
  mov    -0x50(%rbp),%rdx
  add    %rdx,%rax
  and    $0x1,%eax
  or     %rax,-0x60(%rbp)
  andq   $0x3fffffff,-0x60(%rbp)
  mov    -0x60(%rbp),%rax
  mov    -0x8(%rbp),%rdx
  sub    %fs:0x28,%rdx
  je     L48
  call   <__stack_chk_fail@plt>
L48:
  leave
  ret
```

assistant: ```c
unsigned long computeChecksum(unsigned long source, int nib) {
  unsigned long bmask[6] = {0x3B1F3480UL, 0x1D8F9A40UL, 0x2EC7CD00UL, 0x1763E680UL, 0x2BB1F340UL, 0x0B7A89C0UL};
  unsigned long D;
  unsigned long d = source & 0x3FFFFFC0UL;
  unsigned long D29 = (source >> 31) & 0x1UL;
  unsigned long D30 = (source >> 30) & 0x1UL;
  if (nib) {
    if ((D30 + countBits(bmask[4] & d)) % 2)
      d ^= (0x1UL << 6);
    if ((D29 + countBits(bmask[5] & d)) % 2)
      d ^= (0x1UL << 7);
  }
  D = d;
  if (D30)
    D ^= 0x3FFFFFC0UL;
  D |= ((D29 + countBits(bmask[0] & d)) % 2) << 5;
  D |= ((D30 + countBits(bmask[1] & d)) % 2) << 4;
  D |= ((D29 + countBits(bmask[2] & d)) % 2) << 3;
  D |= ((D30 + countBits(bmask[3] & d)) % 2) << 2;
  D |= ((D30 + countBits(bmask[4] & d)) % 2) << 1;
  D |= ((D29 + countBits(bmask[5] & d)) % 2);
  D &= 0x3FFFFFFFUL;
  return (D);
}
```