[libc-commits] [libc] [libc][math] Qualify fdim funtions to constexpr (PR #194137)

[Kiriti Ponduri via libc-commits]

================
@@ -98,11 +103,15 @@ add_or_sub(InType x, InType y) {
       if (y_bits.is_zero()) {
         if (is_effectively_add)
           return OutFPBits::zero(x_bits.sign()).get_val();
-        switch (fputil::quick_get_round()) {
-        case FE_DOWNWARD:
-          return OutFPBits::zero(Sign::NEG).get_val();
-        default:
+        if (__builtin_is_constant_evaluated()) {
           return OutFPBits::zero(Sign::POS).get_val();
----------------
udaykiriti wrote:

LIBC_INLINE int quick_get_round() {
  static volatile float x = 0x1.0p-24f;
  float y = x;
  float z = (0x1.000002p0f + y) + (-1.0f - y);

  if (z == 0.0f)
    return FE_DOWNWARD;
  if (z == 0x1.0p-23f)
    return FE_TOWARDZERO;
  return (2.0f + y == 2.0f) ? FE_TONEAREST : FE_UPWARD;
}

it is coming from this functions and it is using volatile keyword and it gives me an error.

https://github.com/llvm/llvm-project/pull/194137