Of course C easily allows you to directly write SIMD routines via intrinsic instructions or inline assembly:

```

  generic
     type T is private;
     Aligned : Bool := True;
  function Inverse_Sqrt_T (V : T) return T;
  function Inverse_Sqrt_T (V : T) return T is
    Result : aliased T;
    THREE         : constant Real   := 3.0;
    NEGATIVE_HALF : constant Real   := -0.5;
    VMOVPS        : constant String := (if Aligned then "vmovaps" else "vmovups");
    begin
      Asm (Clobber  => "xmm0, xmm1, xmm2, xmm3, memory",
           Inputs   => (Ptr'Asm_Input ("r", Result'Address),
                        Ptr'Asm_Input ("r", V'Address),
                        Ptr'Asm_Input ("r", THREE'Address),
                        Ptr'Asm_Input ("r", NEGATIVE_HALF'Address)),                     
           Template => VMOVPS & "       (%1), %%xmm0         " & E & --   xmm0 ← V
                       " vrsqrtps     %%xmm0, %%xmm1         " & E & --   xmm1 ← Reciprocal sqrt of xmm0
                       " vmulps       %%xmm1, %%xmm1, %%xmm2 " & E & --   xmm2 ← xmm1 \* xmm1
                       " vbroadcastss   (%2), %%xmm3         " & E & --   xmm3 ← NEGATIVE_HALF
                       " vfmsub231ps  %%xmm2, %%xmm0, %%xmm3 " & E & --   xmm3 ← (V - xmm2) \* NEGATIVE_HALF
                       " vbroadcastss   (%3), %%xmm0         " & E & --   xmm0 ← THREE
                       " vmulps       %%xmm0, %%xmm1, %%xmm0 " & E & --   xmm0 ← THREE \* xmm1
                       " vmulps       %%xmm3, %%xmm0, %%xmm0 " & E & --   xmm0 ← xmm3 \* xmm0
                       VMOVPS & "     %%xmm0,   (%0)         ");     -- Result ← xmm0
      return Result;
    end;

  function Inverse_Sqrt is new Inverse_Sqrt_T (Vector_2D, Aligned => False);
  function Inverse_Sqrt is new Inverse_Sqrt_T (Vector_3D, Aligned => False);
  function Inverse_Sqrt is new Inverse_Sqrt_T (Vector_4D);

```

```C

  vector_3d vector_inverse_sqrt(const vector_3d\* v) {
  ...
  vector_4d vector_inverse_sqrt(const vector_4d\* v) {
    vector_4d out;
    static const float THREE = 3.0f;          // 0x40400000
    static const float NEGATIVE_HALF = -0.5f; // 0xbf000000

    __asm__ (
        // Load the input vector into xmm0
        "vmovaps        (%1), %%xmm0\n\t"
        "vrsqrtps     %%xmm0, %%xmm1\n\t"
        "vmulps       %%xmm1, %%xmm1, %%xmm2\n\t"
        "vbroadcastss   (%2), %%xmm3\n\t"
        "vfmsub231ps  %%xmm2, %%xmm0, %%xmm3\n\t"
        "vbroadcastss   (%3), %%xmm0\n\t"
        "vmulps       %%xmm0, %%xmm1, %%xmm0\n\t"
        "vmulps       %%xmm3, %%xmm0, %%xmm0\n\t"
        "vmovups      %%xmm0,   (%0)\n\t"                         // Output operand
        :
        : "r" (&out), "r" (v), "r" (&THREE), "r" (&NEGATIVE_HALF) // Input operands
        : "xmm0", "xmm1", "xmm2", "memory"                        // Clobbered registers
    );

    return out;

} ```