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

```asm
<downlo>:
  endbr64
  push   %rbp
  mov    %rsp,%rbp
  mov    %rdi,-0x28(%rbp)
  mov    %esi,-0x2c(%rbp)
  mov    %rdx,-0x38(%rbp)
  mov    %ecx,-0x30(%rbp)
  mov    %r8,-0x40(%rbp)
  mov    -0x2c(%rbp),%eax
  mov    %eax,%edx
  shr    $0x1f,%edx
  add    %edx,%eax
  sar    %eax
  mov    %eax,-0x10(%rbp)
  mov    -0x30(%rbp),%eax
  mov    %eax,%edx
  shr    $0x1f,%edx
  add    %edx,%eax
  sar    %eax
  mov    %eax,-0xc(%rbp)
  mov    -0x10(%rbp),%eax
  sub    -0xc(%rbp),%eax
  mov    %eax,-0x20(%rbp)
  mov    -0x20(%rbp),%eax
  lea    (%rax,%rax,1),%edx
  mov    -0x30(%rbp),%eax
  sub    $0x1,%eax
  add    %edx,%eax
  cmp    %eax,-0x2c(%rbp)
  jg     L75
  subl   $0x1,-0x20(%rbp)
L75:
  cmpl   $0x0,-0x20(%rbp)
  jns    L87
  movl   $0xffffffff,-0x20(%rbp)
L87:
  movl   $0x0,-0x1c(%rbp)
  jmp    L35
L78:
  pxor   %xmm0,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  movl   $0x0,-0x18(%rbp)
  jmp    L70
L65:
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x1c(%rbp),%eax
  lea    (%rax,%rax,1),%edx
  mov    -0x18(%rbp),%eax
  add    %edx,%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mulsd  %xmm1,%xmm0
  movsd  -0x8(%rbp),%xmm1
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  addl   $0x1,-0x18(%rbp)
L70:
  mov    -0x18(%rbp),%eax
  cmp    -0x30(%rbp),%eax
  jl     L65
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  addl   $0x1,-0x1c(%rbp)
L35:
  mov    -0x1c(%rbp),%eax
  cmp    -0x20(%rbp),%eax
  jle    L78
  mov    -0x20(%rbp),%eax
  add    $0x1,%eax
  mov    %eax,-0x1c(%rbp)
  jmp    L0
L49:
  pxor   %xmm0,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  mov    -0x1c(%rbp),%eax
  add    %eax,%eax
  mov    %eax,-0x14(%rbp)
  movl   $0x0,-0x18(%rbp)
  jmp    L29
L7:
  mov    -0x14(%rbp),%eax
  cmp    -0x2c(%rbp),%eax
  jl     L54
  mov    -0x2c(%rbp),%eax
  sub    %eax,-0x14(%rbp)
L54:
  mov    -0x18(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x38(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm1
  mov    -0x14(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x28(%rbp),%rax
  add    %rdx,%rax
  movsd  (%rax),%xmm0
  mulsd  %xmm1,%xmm0
  movsd  -0x8(%rbp),%xmm1
  addsd  %xmm1,%xmm0
  movsd  %xmm0,-0x8(%rbp)
  addl   $0x1,-0x14(%rbp)
  addl   $0x1,-0x18(%rbp)
L29:
  mov    -0x18(%rbp),%eax
  cmp    -0x30(%rbp),%eax
  jl     L7
  mov    -0x1c(%rbp),%eax
  cltq
  lea    0x0(,%rax,8),%rdx
  mov    -0x40(%rbp),%rax
  add    %rdx,%rax
  movsd  -0x8(%rbp),%xmm0
  movsd  %xmm0,(%rax)
  addl   $0x1,-0x1c(%rbp)
L0:
  mov    -0x1c(%rbp),%eax
  cmp    -0x10(%rbp),%eax
  jl     L49
  nop
  nop
  pop    %rbp
  ret
```

assistant: ```c
void downlo(x, n, lpf, m, y) double x[], lpf[], y[];
int n, m;
{
  int n2, mlo, mhi, i, h, j;
  double s;
  n2 = n / 2;
  mlo = m / 2;
  mhi = n2 - mlo;
  if (2 * mhi + (m - 1) >= n)
    --mhi;
  if (mhi < 0)
    mhi = -1;
  for (i = 0; i <= mhi; i++) {
    s = 0.;
    for (h = 0; h < m; h++)
      s += lpf[h] * x[2 * i + h];
    y[i] = s;
  }
  for (i = mhi + 1; i < n2; i++) {
    s = 0.;
    j = 2 * i;
    for (h = 0; h < m; h++) {
      if (j >= n)
        j -= n;
      s += lpf[h] * x[j];
      j++;
    }
    y[i] = s;
  }
}
```