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

```asm
<lubksb>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x28(%rbp)
  mov    %esi,-0x2c(%rbp)
  mov    %rdx,-0x38(%rbp)
  mov    %rcx,-0x40(%rbp)
  movl   $0xffffffff,-0x14(%rbp)
  movl   $0x0,-0x18(%rbp)
  jmp    L42
L80:
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  mov    (%rax),%eax
  mov    %eax,-0xc(%rbp)
  mov    -0xc(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  movsd  %xmm0,-0x8(%rbp)
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rax,%rdx
  mov    -0xc(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rcx
  mov    -0x40(%rbp),%rax
  add    %rcx,%rax
  movsd  (%rdx),%xmm0
  movsd  %xmm0,(%rax)
  cmpl   $0x0,-0x14(%rbp)
  js     L8
  mov    -0x14(%rbp),%eax
  mov    %eax,-0x10(%rbp)
  jmp    L109
L89:
  mov    -0x10(%rbp),%eax
  imul   -0x2c(%rbp),%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x10(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mulsd  %xmm0,%xmm1
  movsd  -0x8(%rbp),%xmm0
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  addl   $0x1,-0x10(%rbp)
L109:
  mov    -0x10(%rbp),%eax
  cmp    -0x18(%rbp),%eax
  jl     L89
  jmp    L66
L8:
  pxor   %xmm0,%xmm0
  ucomisd -0x8(%rbp),%xmm0
  jp     L15
  pxor   %xmm0,%xmm0
  ucomisd -0x8(%rbp),%xmm0
  je     L66
L15:
  mov    -0x18(%rbp),%eax
  mov    %eax,-0x14(%rbp)
L66:
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  addl   $0x1,-0x18(%rbp)
L42:
  mov    -0x18(%rbp),%eax
  cmp    -0x2c(%rbp),%eax
  jl     L80
  mov    -0x2c(%rbp),%eax
  sub    $0x1,%eax
  mov    %eax,-0x18(%rbp)
  jmp    L113
L85:
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  movsd  %xmm0,-0x8(%rbp)
  mov    -0x18(%rbp),%eax
  add    $0x1,%eax
  mov    %eax,-0x10(%rbp)
  jmp    L75
L13:
  mov    -0x10(%rbp),%eax
  imul   -0x2c(%rbp),%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x10(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mulsd  %xmm0,%xmm1
  movsd  -0x8(%rbp),%xmm0
  subsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  addl   $0x1,-0x10(%rbp)
L75:
  mov    -0x10(%rbp),%eax
  cmp    -0x2c(%rbp),%eax
  jl     L13
  mov    -0x18(%rbp),%eax
  imul   -0x2c(%rbp),%eax
  mov    %eax,%edx
  mov    -0x18(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x8(%rbp),%xmm0
  divsd  %xmm1,%xmm0
  movsd  %xmm0,(%rax)
  subl   $0x1,-0x18(%rbp)
L113:
  cmpl   $0x0,-0x18(%rbp)
  jns    L85
  nop
  nop
  pop    %rbp
  ret
```

assistant: ```c
void lubksb(const double *A, int n, const int *indx, double *b) {
  double s;
  int i, ii = -1, ip, j;
  for (i = 0; i < n; i++) {
    ip = indx[i];
    s = b[ip];
    b[ip] = b[i];
    if (ii >= 0)
      for (j = ii; j < i; j++)
        s -= A[i + j * n] * b[j];
    else if (s)
      ii = i;
    b[i] = s;
  }
  for (i = n - 1; i >= 0; i--) {
    s = b[i];
    for (j = i + 1; j < n; j++)
      s -= A[i + j * n] * b[j];
    b[i] = s / A[i + i * n];
  }
}
```