user: What would the C source look like for the assembly code provided here?

```asm
<lubksb>:
  endbr64
  test   %edx,%edx
  jle    L120
  push   %r13
  mov    %rcx,%r10
  mov    %edx,%r8d
  mov    $0x1,%ecx
  push   %r12
  xor    %r9d,%r9d
  mov    $0x1,%eax
  pxor   %xmm2,%xmm2
  push   %rbp
  push   %rbx
  nopl   0x0(%rax)
L16:
  movslq (%r10,%rcx,4),%rdx
  movsd  (%rsi,%rcx,8),%xmm1
  lea    (%rsi,%rdx,8),%rdx
  movsd  (%rdx),%xmm0
  movsd  %xmm1,(%rdx)
  test   %r9d,%r9d
  jne    L203
  ucomisd %xmm2,%xmm0
  jp     L213
  je     L110
L213:
  mov    %eax,%r9d
L110:
  add    $0x1,%eax
  movsd  %xmm0,(%rsi,%rcx,8)
  cmp    %r8d,%eax
  jg     L140
  add    $0x1,%rcx
  jmp    L16
  nopl   0x0(%rax)
L203:
  cmp    %r9d,%eax
  jle    L40
  mov    %eax,%r12d
  mov    (%rdi,%rcx,8),%rbp
  sub    %r9d,%r12d
  cmp    $0x1,%r12d
  je     L176
  movslq %r9d,%r11
  mov    %r12d,%ebx
  xor    %edx,%edx
  shl    $0x3,%r11
  shr    %ebx
  lea    0x0(%rbp,%r11,1),%r13
  shl    $0x4,%rbx
  add    %rsi,%r11
  nopl   0x0(%rax,%rax,1)
L3:
  movupd 0x0(%r13,%rdx,1),%xmm1
  movupd (%r11,%rdx,1),%xmm4
  add    $0x10,%rdx
  mulpd  %xmm4,%xmm1
  subsd  %xmm1,%xmm0
  unpckhpd %xmm1,%xmm1
  subsd  %xmm1,%xmm0
  cmp    %rbx,%rdx
  jne    L3
  mov    %r12d,%r11d
  and    $0xfffffffe,%r11d
  lea    (%r11,%r9,1),%edx
  cmp    %r11d,%r12d
  je     L40
L94:
  movslq %edx,%rdx
  movsd  0x0(%rbp,%rdx,8),%xmm1
  mulsd  (%rsi,%rdx,8),%xmm1
  subsd  %xmm1,%xmm0
L40:
  lea    0x1(%rax),%edx
  movsd  %xmm0,(%rsi,%rcx,8)
  cmp    %edx,%r8d
  jl     L140
  movslq %r9d,%rbx
  movslq %edx,%rax
  sub    %r9d,%edx
  shl    $0x3,%rbx
  lea    (%rsi,%rbx,1),%r11
  nopw   0x0(%rax,%rax,1)
L214:
  movslq (%r10,%rax,4),%rcx
  movsd  (%rsi,%rax,8),%xmm1
  lea    (%rsi,%rcx,8),%rcx
  movsd  (%rcx),%xmm0
  movsd  %xmm1,(%rcx)
  cmp    %eax,%r9d
  jge    L54
  mov    (%rdi,%rax,8),%rbp
  cmp    $0x1,%edx
  je     L156
  mov    %edx,%r12d
  lea    0x0(%rbp,%rbx,1),%r13
  xor    %ecx,%ecx
  shr    %r12d
  shl    $0x4,%r12
L158:
  movupd 0x0(%r13,%rcx,1),%xmm1
  movupd (%r11,%rcx,1),%xmm5
  add    $0x10,%rcx
  mulpd  %xmm5,%xmm1
  subsd  %xmm1,%xmm0
  unpckhpd %xmm1,%xmm1
  subsd  %xmm1,%xmm0
  cmp    %rcx,%r12
  jne    L158
  mov    %edx,%r12d
  and    $0xfffffffe,%r12d
  lea    (%r12,%r9,1),%ecx
  cmp    %r12d,%edx
  je     L54
L204:
  movslq %ecx,%rcx
  movsd  0x0(%rbp,%rcx,8),%xmm1
  mulsd  (%rsi,%rcx,8),%xmm1
  subsd  %xmm1,%xmm0
L54:
  movsd  %xmm0,(%rsi,%rax,8)
  add    $0x1,%rax
  add    $0x1,%edx
  cmp    %eax,%r8d
  jge    L214
L140:
  movslq %r8d,%rax
  lea    0x1(%r8),%r10d
  xor    %ecx,%ecx
  lea    0x8(,%rax,8),%r11
  xchg   %ax,%ax
L39:
  mov    %r11,%r9
  mov    %r10d,%eax
  sub    $0x8,%r11
  movsd  -0x8(%rsi,%r9,1),%xmm0
  mov    -0x8(%rdi,%r9,1),%rbx
  cmp    %r10d,%r8d
  jl     L32
  cmp    $0x1,%ecx
  je     L160
  mov    %ecx,%edx
  lea    (%rbx,%r9,1),%r12
  lea    (%rsi,%r9,1),%rbp
  xor    %eax,%eax
  shr    %edx
  shl    $0x4,%rdx
  nopw   0x0(%rax,%rax,1)
L177:
  movupd 0x0(%rbp,%rax,1),%xmm1
  movupd (%r12,%rax,1),%xmm3
  add    $0x10,%rax
  mulpd  %xmm3,%xmm1
  subsd  %xmm1,%xmm0
  unpckhpd %xmm1,%xmm1
  subsd  %xmm1,%xmm0
  cmp    %rax,%rdx
  jne    L177
  mov    %ecx,%edx
  and    $0xfffffffe,%edx
  lea    (%r10,%rdx,1),%eax
  cmp    %ecx,%edx
  je     L32
L160:
  cltq
  movsd  (%rsi,%rax,8),%xmm1
  mulsd  (%rbx,%rax,8),%xmm1
  subsd  %xmm1,%xmm0
L32:
  add    $0x1,%ecx
  divsd  (%rbx,%r11,1),%xmm0
  sub    $0x1,%r10d
  movsd  %xmm0,-0x8(%rsi,%r9,1)
  cmp    %r8d,%ecx
  jne    L39
  pop    %rbx
  pop    %rbp
  pop    %r12
  pop    %r13
  ret
L176:
  mov    %r9d,%edx
  jmp    L94
L156:
  mov    %r9d,%ecx
  jmp    L204
L120:
  ret
```

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