From dfad8317aa566efffb971455b42bfdecbaee5985 Mon Sep 17 00:00:00 2001
From: fonsinchen <fonsinchen@openttd.org>
Date: Sun, 9 Jun 2013 12:50:33 +0000
Subject: [PATCH] (svn r25347) -Add: function for deterministic approximate
 division

---
 src/core/math_func.cpp | 21 +++++++++++++++++++++
 src/core/math_func.hpp |  1 +
 2 files changed, 22 insertions(+)

diff --git a/src/core/math_func.cpp b/src/core/math_func.cpp
index 2b8ca33092..8c136c0bb6 100644
--- a/src/core/math_func.cpp
+++ b/src/core/math_func.cpp
@@ -47,6 +47,27 @@ int GreatestCommonDivisor(int a, int b)
 
 }
 
+/**
+ * Deterministic approximate division.
+ * Cancels out division errors stemming from the integer nature of the division over multiple runs.
+ * @param a Dividend.
+ * @param b Divisor.
+ * @return a/b or (a/b)+1.
+ */
+int DivideApprox(int a, int b)
+{
+	int random_like = ((a + b) * (a - b)) % b;
+
+	int remainder = a % b;
+
+	int ret = a / b;
+	if (abs(random_like) < abs(remainder)) {
+		ret += ((a < 0) ^ (b < 0)) ? -1 : 1;
+	}
+
+	return ret;
+}
+
 /**
  * Compute the integer square root.
  * @param num Radicand.
diff --git a/src/core/math_func.hpp b/src/core/math_func.hpp
index b613d1e6a5..fd41102317 100644
--- a/src/core/math_func.hpp
+++ b/src/core/math_func.hpp
@@ -317,6 +317,7 @@ static inline uint ToPercent16(uint i)
 
 int LeastCommonMultiple(int a, int b);
 int GreatestCommonDivisor(int a, int b);
+int DivideApprox(int a, int b);
 
 /**
  * Computes ceil(a / b) for non-negative a and b.