[libc-commits] [libc] [llvm] [libc][math] Added missing floating point exception for atanpif16 (PR #186597)

[via libc-commits]

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@@ -120,7 +120,19 @@ LLVM_LIBC_FUNCTION(float16, atanpif16, (float16 x)) {
   // Case 1: |x| <= 0.5 - Direct polynomial evaluation
   if (LIBC_LIKELY(x_abs <= 0.5)) {
     double result = atanpi_eval(x_abs);
-    return signed_result(result);
+    float16 s_result = signed_result(result);
+    // clear the underflow raised by casting
+    fputil::clear_except_if_required(FE_UNDERFLOW);
+    int rounding = fputil::quick_get_round();
+    // values checked through exhaustive testing which rounded up/down and
+    // caused spurious or missing underflow
+    bool except_value = (rounding == FE_UPWARD && xbits.uintval() == 0x0a48) ||
+                        (rounding == FE_DOWNWARD && xbits.uintval() == 0x8a48);
+
+    if (result != 0.0 && result < 0x1p-14 && !except_value)
+      fputil::raise_except_if_required(FE_UNDERFLOW);
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Sukumarsawant wrote:

I did try to remove it completely, but it does miss raising an exception for some values.

```CPP
    if (FPBits(s_result).is_subnormal())
      fputil::raise_except_if_required(FE_UNDERFLOW);
 ```
 removed the except value condition since it's handled before that and returns early.

https://github.com/llvm/llvm-project/pull/186597