[libc-commits] [libc] [libc][math] Add bit-rounding roundf implementation (PR #221648)

[via libc-commits]

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@@ -109,48 +109,41 @@ LIBC_INLINE constexpr T round(T x) {
   using StorageType = typename FPBits<T>::StorageType;
   FPBits<T> bits(x);
 
-  // If x is infinity NaN or zero, return it.
-  if (bits.is_inf_or_nan() || bits.is_zero())
-    return x;
+  // x86 binary80 has NaN encodings with a non-all-ones exponent, so the
+  // biased-exponent check below does not cover every NaN representation.
+  if constexpr (get_fp_type<T>() == FPType::X86_Binary80) {
+    if (bits.is_nan())
+      return x;
+  }
 
-  int exponent = bits.get_exponent();
+  uint16_t biased_exponent = bits.get_biased_exponent();
 
-  // If the exponent is greater than the most negative mantissa
-  // exponent, then x is already an integer.
-  if (exponent >= static_cast<int>(FPBits<T>::FRACTION_LEN))
+  // If x is infinity, NaN, or has no fractional bits, return it.
+  if (biased_exponent >= FPBits<T>::EXP_BIAS + FPBits<T>::FRACTION_LEN)
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sriramshastry wrote:

Done, the high biased-exponent check is now wrapped with `LIBC_UNLIKELY`.

https://github.com/llvm/llvm-project/pull/221648