[CRT:MATH] Implement _isnan and _isnanf

Author: tkreuzer

dll/win32/ucrtbase/ucrtbase.spec

@@ -560,7 +560,7 @@
 @ cdecl _ismbstrail(ptr ptr)
 @ cdecl _ismbstrail_l(ptr ptr ptr)
 @ cdecl _isnan(double)
-@ cdecl -stub -arch=x86_64 _isnanf(float)
+@ cdecl -arch=x86_64 _isnanf(float)
 @ cdecl _isprint_l(long ptr)
 @ cdecl _ispunct_l(long ptr)
 @ cdecl _isspace_l(long ptr)

sdk/lib/crt/float/float.cmake

@@ -1,8 +1,4 @@
 
-list(APPEND LIBCNTPR_FLOAT_SOURCE
-    float/isnan.c
-)
-
 list(APPEND CRT_FLOAT_SOURCE
     ${LIBCNTPR_FLOAT_SOURCE}
     float/chgsign.c

sdk/lib/crt/float/isnan.c

@@ -0,0 +1,17 @@
+/*
+ * PROJECT:     ReactOS CRT
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Implementation of _isnan.
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <[email protected]>
+ */
+
+#include <float.h>
+#include <stdint.h>
+
+int
+__cdecl
+_isnan(_In_ double _X)
+{
+    union { double f; uint64_t ui64; } u = { _X };
+    return (u.ui64 & ~0x8000000000000000ull) > 0x7FF0000000000000ull;
+}

sdk/lib/crt/math/_isnan.c

@@ -0,0 +1,17 @@
+/*
+ * PROJECT:     ReactOS CRT
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Implementation of _isnanf.
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <[email protected]>
+ */
+
+#include <math.h>
+#include <stdint.h>
+
+int
+__cdecl
+_isnanf(_In_ float _X)
+{
+    union { float f; uint32_t ui32; } u = { _X };
+    return (u.ui32 & ~0x80000000) > 0x7F800000;
+}

sdk/lib/crt/math/_isnanf.c

@@ -7,6 +7,8 @@ list(APPEND LIBCNTPR_MATH_SOURCE
     math/_fdsign.c
     math/_finite.c
     math/_finitef.c
+    math/_isnan.c
+    math/_isnanf.c
     math/_invoke_matherr.c
     math/abs.c
     math/div.c