Fix double to unlong conversions to handle NaN (#70331)

This was apparently fixed in 2016 on CoreCLR but no tests were added.

The generic math tests are the first things that exercise this.

Doesn't fail in the CI because this helper is likely not needed on ARM64 and we only test libs with NativeAOT on ARM64.

Thought this was because of my local changes (because the CI was clean) but wasn't. Spent more time on this than I would be willing to admit.

2 files changed, 50 insertions, 1 deletions

diff --git a/src/coreclr/nativeaot/Runtime/CommonMacros.h b/src/coreclr/nativeaot/Runtime/CommonMacros.h
index 46fdcea69da..97f3b32ef4c 100644
--- a/src/coreclr/nativeaot/Runtime/CommonMacros.h
+++ b/src/coreclr/nativeaot/Runtime/CommonMacros.h
@@ -250,4 +250,33 @@ typedef int32_t HRESULT;
 #endif // !defined(_INC_WINDOWS)
 #endif // __GCENV_BASE_INCLUDED__
 
+// PAL Numbers
+// Used to ensure cross-compiler compatibility when declaring large
+// integer constants. 64-bit integer constants should be wrapped in the
+// declarations listed here.
+//
+// Each of the #defines here is wrapped to avoid conflicts with pal.h.
+
+#if defined(_MSC_VER)
+
+// MSVC's way of declaring large integer constants
+// If you define these in one step, without the _HELPER macros, you
+// get extra whitespace when composing these with other concatenating macros.
+#ifndef I64
+#define I64_HELPER(x) x ## i64
+#define I64(x)        I64_HELPER(x)
+#endif
+
+#else
+
+// GCC's way of declaring large integer constants
+// If you define these in one step, without the _HELPER macros, you
+// get extra whitespace when composing these with other concatenating macros.
+#ifndef I64
+#define I64_HELPER(x) x ## LL
+#define I64(x)        I64_HELPER(x)
+#endif
+
+#endif
+
 #endif // __COMMONMACROS_H__
diff --git a/src/coreclr/nativeaot/Runtime/MathHelpers.cpp b/src/coreclr/nativeaot/Runtime/MathHelpers.cpp
index c5bc94ee09a..9ad553ce156 100644
--- a/src/coreclr/nativeaot/Runtime/MathHelpers.cpp
+++ b/src/coreclr/nativeaot/Runtime/MathHelpers.cpp
@@ -9,9 +9,29 @@
 // Floating point and 64-bit integer math helpers.
 //
 
+FORCEINLINE int64_t FastDbl2Lng(double val)
+{
+#ifdef TARGET_X86
+    return HCCALL1_V(JIT_Dbl2Lng, val);
+#else
+    return((__int64) val);
+#endif
+}
+
 EXTERN_C NATIVEAOT_API uint64_t REDHAWK_CALLCONV RhpDbl2ULng(double val)
 {
-    return((uint64_t)val);
+    const double two63  = 2147483648.0 * 4294967296.0;
+    uint64_t ret;
+    if (val < two63)
+    {
+        ret = FastDbl2Lng(val);
+    }
+    else
+    {
+        // subtract 0x8000000000000000, do the convert then add it back again
+        ret = FastDbl2Lng(val - two63) + I64(0x8000000000000000);
+    }
+    return ret;
 }
 
 #undef min