user: Demonstrate the C code that generates the assembly output below:

```asm
<update>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %edi,-0x14(%rbp)
  movss  %xmm0,-0x18(%rbp)
  mov    %esi,-0x1c(%rbp)
  mov    %rdx,-0x28(%rbp)
  movl   $0x2,-0x4(%rbp)
  jmp    L25
L36:
  mov    -0x4(%rbp),%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm1
  mov    -0x4(%rbp),%eax
  sub    $0x1,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm2
  mov    -0x4(%rbp),%eax
  add    $0x1,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm0
  addss  %xmm2,%xmm0
  mulss  -0x18(%rbp),%xmm0
  mov    -0x4(%rbp),%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  addss  %xmm1,%xmm0
  movss  %xmm0,(%rax)
  addl   $0x2,-0x4(%rbp)
L25:
  mov    -0x14(%rbp),%eax
  sub    $0x1,%eax
  cmp    %eax,-0x4(%rbp)
  jl     L36
  mov    -0x14(%rbp),%eax
  and    $0x1,%eax
  test   %eax,%eax
  jne    L26
  mov    -0x28(%rbp),%rax
  movss  (%rax),%xmm1
  mov    -0x14(%rbp),%eax
  sub    $0x1,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm2
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm0
  addss  %xmm2,%xmm0
  mulss  -0x18(%rbp),%xmm0
  addss  %xmm1,%xmm0
  mov    -0x28(%rbp),%rax
  movss  %xmm0,(%rax)
  jmp    L34
L26:
  mov    -0x28(%rbp),%rax
  movss  (%rax),%xmm0
  pxor   %xmm1,%xmm1
  cvtss2sd %xmm0,%xmm1
  pxor   %xmm0,%xmm0
  cvtss2sd -0x18(%rbp),%xmm0
  movapd %xmm0,%xmm2
  addsd  %xmm0,%xmm2
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm0
  cvtss2sd %xmm0,%xmm0
  mulsd  %xmm2,%xmm0
  addsd  %xmm1,%xmm0
  cvtsd2ss %xmm0,%xmm0
  mov    -0x28(%rbp),%rax
  movss  %xmm0,(%rax)
  mov    -0x14(%rbp),%eax
  sub    $0x1,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm0
  pxor   %xmm1,%xmm1
  cvtss2sd %xmm0,%xmm1
  pxor   %xmm0,%xmm0
  cvtss2sd -0x18(%rbp),%xmm0
  movapd %xmm0,%xmm2
  addsd  %xmm0,%xmm2
  mov    -0x14(%rbp),%eax
  sub    $0x2,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movss  (%rax),%xmm0
  cvtss2sd %xmm0,%xmm0
  mulsd  %xmm2,%xmm0
  addsd  %xmm1,%xmm0
  mov    -0x14(%rbp),%eax
  sub    $0x1,%eax
  imul   -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,4),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  cvtsd2ss %xmm0,%xmm0
  movss  %xmm0,(%rax)
L34:
  nop
  pop    %rbp
  ret
```

assistant: ```c
void update(int n, float a, int str, float *x) {
  for (int i = 2; i < n - 1; i += 2)
    x[i * str] += a * (x[(i - 1) * str] + x[(i + 1) * str]);
  if (0 == n % 2)
    x[0] += a * (x[(n - 1) * str] + x[1 * str]);
  else {
    x[0] += 2. * a * x[1 * str];
    x[(n - 1) * str] += 2. * a * x[(n - 2) * str];
  }
}
```