diff --git a/Core/Libraries/Source/Lib/Include/Lib/BaseDefines.h b/Core/Libraries/Source/Lib/Include/Lib/BaseDefines.h
index b52ed71f4e1..c87defd9448 100644
--- a/Core/Libraries/Source/Lib/Include/Lib/BaseDefines.h
+++ b/Core/Libraries/Source/Lib/Include/Lib/BaseDefines.h
@@ -31,7 +31,7 @@
 #endif
 
 #if defined(__has_include)
-#if __has_include("gmath.h")
+#if __has_include(<gmath.h>)
 #define HAS_GAMEMATH (1)
 #endif
 #endif
diff --git a/Core/Libraries/Source/Lib/Include/Lib/BaseFunctions.h b/Core/Libraries/Source/Lib/Include/Lib/BaseFunctions.h
index c481fb73c0d..4ca2d3ac459 100644
--- a/Core/Libraries/Source/Lib/Include/Lib/BaseFunctions.h
+++ b/Core/Libraries/Source/Lib/Include/Lib/BaseFunctions.h
@@ -21,6 +21,10 @@
 #include <Utility/bit_adapter.h>
 #include "BaseDefines.h"
 
+#if USE_DETERMINISTIC_MATH
+#include <gmath.h>
+#endif
+
 //-----------------------------------------------------------------------------
 inline Real rad2deg(Real rad) { return rad * (180/PI); }
 inline Real deg2rad(Real rad) { return rad * (PI/180); }
@@ -46,8 +50,11 @@ __forceinline long fast_float2long_round(float f)
 	return i;
 }
 
+#if RTS_ZEROHOUR && RETAIL_COMPATIBLE_CRC
 // super fast float trunc routine, works always (independent of any FPU modes)
 // code courtesy of Martin Hoffesommer (grin)
+// TheSuperHackers @info The shift count wraps at 32, so magnitudes of 2^32 and larger lose
+// bits that are not fractional, and NaN becomes infinity. Retail Zero Hour depends on these results.
 __forceinline float fast_float_trunc(float f)
 {
 #if defined(_MSC_VER) && _MSC_VER < 1300
@@ -75,6 +82,10 @@ __forceinline float fast_float_trunc(float f)
 }
 
 // same here, fast floor function
+// TheSuperHackers @info Subtracting almost 1 only floors correctly if the FPU rounds toward zero, but the game
+// rounds to nearest (see setFPMode). So negative whole numbers above -2^24 return n-1, for example -2 returns -3.
+// Negative values closer to zero than about 3e-8 also return 0 instead of -1.
+// Retail Zero Hour depends on these results.
 __forceinline float fast_float_floor(float f)
 {
   static unsigned almost1=(126<<23)|0x7fffff;
@@ -84,6 +95,10 @@ __forceinline float fast_float_floor(float f)
 }
 
 // same here, fast ceil function
+// TheSuperHackers @info Adding almost 1 only ceils correctly if the FPU rounds toward zero, but the game
+// rounds to nearest (see setFPMode). So positive whole numbers below 2^24 return n+1, for example 2 returns 3.
+// Positive values closer to zero than about 3e-8 also return 0 instead of 1.
+// Retail Zero Hour depends on these results.
 __forceinline float fast_float_ceil(float f)
 {
   static unsigned almost1=(126<<23)|0x7fffff;
@@ -91,14 +106,20 @@ __forceinline float fast_float_ceil(float f)
     f+=std::bit_cast<float>(almost1);
   return fast_float_trunc(f);
 }
+#endif // RTS_ZEROHOUR && RETAIL_COMPATIBLE_CRC
 
-// once we've ceiled/floored, trunc and round are identical, and currently, round is faster... (srj)
-#if RTS_GENERALS && RETAIL_COMPATIBLE_CRC
-#define REAL_TO_INT_CEIL(x)				(fast_float2long_round(ceilf(x)))
-#define REAL_TO_INT_FLOOR(x)			(fast_float2long_round(floorf(x)))
+#if RTS_ZEROHOUR && RETAIL_COMPATIBLE_CRC
+	// once we've ceiled/floored, trunc and round are identical, and currently, round is faster... (srj)
+	#define REAL_TO_INT_CEIL(x) (fast_float2long_round(fast_float_ceil(x)))
+	#define REAL_TO_INT_FLOOR(x) (fast_float2long_round(fast_float_floor(x)))
 #else
-#define REAL_TO_INT_CEIL(x)				(fast_float2long_round(fast_float_ceil(x)))
-#define REAL_TO_INT_FLOOR(x)			(fast_float2long_round(fast_float_floor(x)))
+	#if USE_DETERMINISTIC_MATH
+		#define REAL_TO_INT_CEIL(x) (fast_float2long_round(gm_ceilf(x)))
+		#define REAL_TO_INT_FLOOR(x) (fast_float2long_round(gm_floorf(x)))
+	#else
+		#define REAL_TO_INT_CEIL(x) (fast_float2long_round(ceilf(x)))
+		#define REAL_TO_INT_FLOOR(x) (fast_float2long_round(floorf(x)))
+	#endif
 #endif
 
 //-------------------------------------------------------------------------------------------------
diff --git a/Core/Libraries/Source/Lib/Trig.cpp b/Core/Libraries/Source/Lib/Trig.cpp
index 813907cdacd..b1c1492848b 100644
--- a/Core/Libraries/Source/Lib/Trig.cpp
+++ b/Core/Libraries/Source/Lib/Trig.cpp
@@ -33,7 +33,7 @@
 #include "Lib/trig.h"
 
 #if USE_DETERMINISTIC_MATH
-#include "gmath.h"
+#include <gmath.h>
 #endif
 
 Real Sin(Real x)
diff --git a/Core/Libraries/Source/WWVegas/WWMath/wwmath.h b/Core/Libraries/Source/WWVegas/WWMath/wwmath.h
index ff5b3649bd9..d27e4525315 100644
--- a/Core/Libraries/Source/WWVegas/WWMath/wwmath.h
+++ b/Core/Libraries/Source/WWVegas/WWMath/wwmath.h
@@ -44,7 +44,7 @@
 #include "Lib/BaseDefines.h"
 
 #if USE_DETERMINISTIC_MATH
-#include "gmath.h"
+#include <gmath.h>
 #endif
 
 /*