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

```asm
<kernel_dtrmv_u_n_2_lib4>:
  endbr64
  test   %edi,%edi
  jle    L23
  push   %rbx
  movupd (%rdx),%xmm0
  mov    %edi,%r9d
  lea    0x40(%rsi),%rdi
  movsd  (%rsi),%xmm1
  mulsd  (%rdx),%xmm1
  mov    %rsi,%rax
  prefetcht0 (%rsi)
  movupd 0x20(%rsi),%xmm4
  unpckhpd %xmm0,%xmm0
  addsd  D9(%rip),%xmm1
  prefetcht0 0x80(%rsi)
  prefetcht0 0xc0(%rsi)
  mov    %rcx,%r10
  lea    0x10(%rdx),%rsi
  prefetcht0 (%rdi)
  mulpd  %xmm4,%xmm0
  movq   %xmm1,%xmm1
  addpd  %xmm0,%xmm1
  cmp    $0x5,%r9d
  jle    L13
  lea    -0x6(%r9),%ebx
  shr    $0x2,%ebx
  mov    %ebx,%r11d
  mov    %r11,%rdx
  shl    $0x7,%rdx
  lea    0xc0(%rax,%rdx,1),%rcx
  mov    %rsi,%rdx
  mov    %rdi,%rax
  nopl   0x0(%rax)
L53:
  movupd (%rdx),%xmm0
  movupd (%rax),%xmm4
  sub    $0xffffffffffffff80,%rax
  add    $0x20,%rdx
  movupd -0x60(%rax),%xmm5
  movupd -0x40(%rax),%xmm6
  prefetcht0 (%rax)
  prefetcht0 0x40(%rax)
  unpcklpd %xmm0,%xmm0
  movupd -0x20(%rax),%xmm7
  mulpd  %xmm4,%xmm0
  addpd  %xmm1,%xmm0
  movupd -0x20(%rdx),%xmm1
  unpckhpd %xmm1,%xmm1
  mulpd  %xmm5,%xmm1
  addpd  %xmm1,%xmm0
  movupd -0x10(%rdx),%xmm1
  unpcklpd %xmm1,%xmm1
  mulpd  %xmm6,%xmm1
  addpd  %xmm1,%xmm0
  movupd -0x10(%rdx),%xmm1
  unpckhpd %xmm1,%xmm1
  mulpd  %xmm7,%xmm1
  addpd  %xmm0,%xmm1
  cmp    %rcx,%rax
  jne    L53
  lea    0x1(%r11),%rax
  mov    %rax,%rdx
  shl    $0x5,%rax
  shl    $0x7,%rdx
  add    %rax,%rsi
  add    %rdx,%rdi
  lea    0x6(,%rbx,4),%edx
L31:
  cmp    %edx,%r9d
  jle    L81
  lea    -0x1(%r9),%eax
  sub    %edx,%eax
  cmp    $0x1,%eax
  jbe    L25
  movupd (%rdi),%xmm2
  movupd 0x20(%rdi),%xmm0
  and    $0xfffffffe,%eax
  movupd (%rsi),%xmm3
  mov    %eax,%ecx
  add    %eax,%edx
  movhpd 0x30(%rdi),%xmm0
  movhpd 0x10(%rdi),%xmm2
  mov    %rcx,%r11
  unpcklpd %xmm0,%xmm2
  movupd 0x10(%rdi),%xmm0
  movlpd 0x8(%rdi),%xmm0
  shl    $0x5,%r11
  mulpd  %xmm3,%xmm2
  movupd 0x30(%rdi),%xmm3
  movlpd 0x28(%rdi),%xmm3
  add    %r11,%rdi
  unpcklpd %xmm3,%xmm0
  movupd (%rsi),%xmm3
  lea    (%rsi,%rcx,8),%rsi
  mulpd  %xmm3,%xmm0
  movapd %xmm2,%xmm3
  unpcklpd %xmm0,%xmm3
  unpckhpd %xmm0,%xmm2
  addpd  %xmm3,%xmm1
  addpd  %xmm2,%xmm1
L25:
  movsd  (%rsi),%xmm0
  movupd (%rdi),%xmm5
  add    $0x1,%edx
  unpcklpd %xmm0,%xmm0
  mulpd  %xmm5,%xmm0
  addpd  %xmm0,%xmm1
  cmp    %edx,%r9d
  jle    L81
  movsd  0x8(%rsi),%xmm2
  movupd 0x20(%rdi),%xmm0
  unpcklpd %xmm2,%xmm2
  mulpd  %xmm2,%xmm0
  addpd  %xmm0,%xmm1
L81:
  test   %r8d,%r8d
  je     L3
  movupd (%r10),%xmm0
  cmp    $0x1,%r8d
  je     L6
  subpd  %xmm1,%xmm0
  movups %xmm0,(%r10)
  pop    %rbx
  ret
  cs nopw 0x0(%rax,%rax,1)
L3:
  movups %xmm1,(%r10)
  pop    %rbx
  ret
  cs nopw 0x0(%rax,%rax,1)
L23:
  ret
  nopl   0x0(%rax)
L6:
  addpd  %xmm1,%xmm0
  movups %xmm0,(%r10)
  pop    %rbx
  ret
  nopw   0x0(%rax,%rax,1)
L13:
  mov    $0x2,%edx
  jmp    L31
```

tool_calls: name: unpack_data
arguments: data_tag: D9
type_guessed: f64

tool: D9: 0

assistant: ```c
void kernel_dtrmv_u_n_2_lib4(int kmax, double *A, double *x, double *y, int alg) {
  if (kmax <= 0)
    return;
  __builtin_prefetch(A);
  __builtin_prefetch(A + 8);
  const int lda = 4;
  int k;
  double x_0, x_1, x_2, x_3, y_0 = 0, y_1 = 0;
  __builtin_prefetch(A + 4 * lda);
  __builtin_prefetch(A + 4 * lda + 8);
  x_0 = x[0];
  x_1 = x[1];
  y_0 += A[0 + lda * 0] * x_0;
  y_0 += A[0 + lda * 1] * x_1;
  y_1 += A[1 + lda * 1] * x_1;
  A += 2 * lda;
  x += 2;
  k = 2;
  for (; k < kmax - 3; k += 4) {
    __builtin_prefetch(A + 4 * lda);
    __builtin_prefetch(A + 4 * lda + 8);
    x_0 = x[0];
    x_1 = x[1];
    x_2 = x[2];
    x_3 = x[3];
    y_0 += A[0 + lda * 0] * x_0;
    y_1 += A[1 + lda * 0] * x_0;
    y_0 += A[0 + lda * 1] * x_1;
    y_1 += A[1 + lda * 1] * x_1;
    y_0 += A[0 + lda * 2] * x_2;
    y_1 += A[1 + lda * 2] * x_2;
    y_0 += A[0 + lda * 3] * x_3;
    y_1 += A[1 + lda * 3] * x_3;
    A += 4 * lda;
    x += 4;
  }
  for (; k < kmax; k++) {
    x_0 = x[0];
    y_0 += A[0 + lda * 0] * x_0;
    y_1 += A[1 + lda * 0] * x_0;
    A += 1 * lda;
    x += 1;
  }
  if (alg == 0) {
    y[0] = y_0;
    y[1] = y_1;
  } else if (alg == 1) {
    y[0] += y_0;
    y[1] += y_1;
  } else {
    y[0] -= y_0;
    y[1] -= y_1;
  }
}
```