[CRT:MATH] Implement _dsign and _dsignf

dll/win32/ucrtbase/ucrtbase.spec

@@ -306,7 +306,7 @@
 @ cdecl -stub _dpcomp(double double)
 @ cdecl -stub _dpoly(double ptr long)
 @ cdecl -stub _dscale(ptr long)
-@ cdecl -stub _dsign(double)
+@ cdecl _dsign(double)
 @ cdecl -stub _dsin(double long)
 @ cdecl _dtest(ptr)
 @ cdecl -stub _dunscale(ptr ptr)
@@ -349,7 +349,7 @@
 @ cdecl -stub _fdpcomp(float float)
 @ cdecl -stub _fdpoly(float ptr long)
 @ cdecl -stub _fdscale(ptr long)
-@ cdecl -stub _fdsign(float)
+@ cdecl _fdsign(float)
 @ cdecl -stub _fdsin(float long)
 @ cdecl _fdtest(ptr)
 @ cdecl -stub _fdunscale(ptr ptr)

sdk/lib/crt/math/_dsign.c

@@ -0,0 +1,20 @@
+/*
+ * PROJECT:     ReactOS CRT
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Implementation of _dsign.
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <timo.kreuzer@reactos.org>
+ */
+
+#include <math.h>
+#include <stdint.h>
+
+_Check_return_
+int
+__cdecl
+_dsign(_In_ double _X)
+{
+    union { double f; uint64_t ui64; } u = { _X };
+
+    // This is what Windows returns
+    return (u.ui64 >> 48) & 0x8000;
+}

sdk/lib/crt/math/_fdsign.c

@@ -0,0 +1,20 @@
+/*
+ * PROJECT:     ReactOS CRT
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Implementation of _fdsign.
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <timo.kreuzer@reactos.org>
+ */
+
+#include <math.h>
+#include <stdint.h>
+
+_Check_return_
+int
+__cdecl
+_fdsign(_In_ float _X)
+{
+    union { float f; uint32_t ui32; } u = { _X };
+
+    // This is what Windows returns
+    return (u.ui32 >> 16) & 0x8000;
+}

sdk/lib/crt/math/math.cmake

@@ -3,6 +3,8 @@ include_directories(libm_sse2)
 
 list(APPEND LIBCNTPR_MATH_SOURCE
     math/_chgsignf.c
+    math/_dsign.c
+    math/_fdsign.c
     math/_invoke_matherr.c
     math/abs.c
     math/div.c