From 5aaf09018f6664620e5b9e987a65429b799a9cd8 Mon Sep 17 00:00:00 2001
From: Jean-Baptiste Perrier <jimi.vacarians@gmail.com>
Date: Wed, 18 Aug 2021 12:49:53 +0200
Subject: [PATCH] Add missing NearEqual for double

---
 Source/Engine/Core/Math/Mathd.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/Source/Engine/Core/Math/Mathd.h b/Source/Engine/Core/Math/Mathd.h
index 47b16b608..8f7ac05b7 100644
--- a/Source/Engine/Core/Math/Mathd.h
+++ b/Source/Engine/Core/Math/Mathd.h
@@ -248,6 +248,34 @@ namespace Math
         return ulp > maxUlp;
     }
 
+    /// <summary>
+        /// Checks if a and b are almost equals, taking into account the magnitude of double precision floating point numbers
+        /// </summary>
+        /// <param name="a">The left value to compare</param>
+        /// <param name="b">The right value to compare</param>
+        /// <returns>True if a almost equal to b, otherwise false</returns>
+        static bool NearEqual(double a, double b)
+        {
+            // Check if the numbers are really close - needed when comparing numbers near zero
+            if (IsZero(a - b))
+                return true;
+    
+            // Original from Bruce Dawson: http://randomascii.wordpress.com/2012/02/25/comparing-floating-point-numbers-2012-edition/
+            const int64 aInt = *(int64*)&a;
+            const int64 bInt = *(int64*)&b;
+    
+            // Different signs means they do not match
+            if (aInt < 0 != bInt < 0)
+                return false;
+    
+            // Find the difference in ULPs
+            const int64 ulp = Abs(aInt - bInt);
+    
+            // Choose of maxUlp = 4
+            // according to http://code.google.com/p/googletest/source/browse/trunk/include/gtest/internal/gtest-internal.h
+            const int maxUlp = 4;
+            return ulp <= maxUlp;
+        }
 
     /// <summary>
     /// Checks if a and b are almost equals within the given epsilon value.