[libc-commits] [libc] [libc][math][c23] Fix X86_80 Special Case (PR #86924)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-libc

Author: Shourya Goel (Sh0g0-1758)

<details>
<summary>Changes</summary>

Updates the special case of pseudo infinty as pointed in #<!-- -->85940

---
Full diff: https://github.com/llvm/llvm-project/pull/86924.diff


2 Files Affected:

- (modified) libc/src/__support/FPUtil/BasicOperations.h (+6-4) 
- (modified) libc/test/src/math/smoke/CanonicalizeTest.h (+3-3) 


``````````diff
diff --git a/libc/src/__support/FPUtil/BasicOperations.h b/libc/src/__support/FPUtil/BasicOperations.h
index a47931bb33900a..bdb91a98a0d357 100644
--- a/libc/src/__support/FPUtil/BasicOperations.h
+++ b/libc/src/__support/FPUtil/BasicOperations.h
@@ -185,7 +185,7 @@ LIBC_INLINE int canonicalize(T &cx, const T &x) {
     // More precisely :
     // Exponent   |       Significand      | Meaning
     //            | Bits 63-62 | Bits 61-0 |
-    // All Ones   |     00     |    Zero   | Pseudo Infinity, Value = Infinty
+    // All Ones   |     00     |    Zero   | Pseudo Infinity, Value = SNaN
     // All Ones   |     00     |  Non-Zero | Pseudo NaN, Value = SNaN
     // All Ones   |     01     | Anything  | Pseudo NaN, Value = SNaN
     //            |   Bit 63   | Bits 62-0 |
@@ -199,9 +199,11 @@ LIBC_INLINE int canonicalize(T &cx, const T &x) {
     int exponent = sx.get_biased_exponent();
     if (exponent == 0x7FFF) {
       if (!bit63 && !bit62) {
-        if (mantissa == 0)
-          cx = FPBits<T>::inf(sx.sign()).get_val();
-        else {
+        if (mantissa == 0) {
+          cx = FPBits<T>::quiet_nan(sx.sign(), mantissa).get_val();
+          raise_except_if_required(FE_INVALID);
+          return 1;
+        } else {
           cx = FPBits<T>::quiet_nan(sx.sign(), mantissa).get_val();
           raise_except_if_required(FE_INVALID);
           return 1;
diff --git a/libc/test/src/math/smoke/CanonicalizeTest.h b/libc/test/src/math/smoke/CanonicalizeTest.h
index c8af83f1983881..1891d47922cf88 100644
--- a/libc/test/src/math/smoke/CanonicalizeTest.h
+++ b/libc/test/src/math/smoke/CanonicalizeTest.h
@@ -55,12 +55,12 @@ class CanonicalizeTest : public LIBC_NAMESPACE::testing::Test {
       T cx;
       // Exponent   |       Significand      | Meaning
       //            | Bits 63-62 | Bits 61-0 |
-      // All Ones   |     00     |    Zero   | Pseudo Infinity, Value = Infinty
+      // All Ones   |     00     |    Zero   | Pseudo Infinity, Value = SNaN
 
       FPBits test1((UInt128(0x7FFF) << 64) + UInt128(0x0000000000000000));
       const T test1_val = test1.get_val();
-      TEST_SPECIAL(cx, test1_val, 0, 0);
-      EXPECT_FP_EQ(cx, inf);
+      TEST_SPECIAL(cx, test1_val, 1, FE_INVALID);
+      EXPECT_FP_EQ(cx, aNaN);
 
       // Exponent   |       Significand      | Meaning
       //            | Bits 63-62 | Bits 61-0 |

``````````

</details>


https://github.com/llvm/llvm-project/pull/86924