From 8c0122f42902363ba682566cd7671dc55f4d0c8c Mon Sep 17 00:00:00 2001
From: rubidium <rubidium@openttd.org>
Date: Sun, 2 Dec 2007 19:21:56 +0000
Subject: (svn r11559) -Fix [FS#1505]: overflow when drawing graphics with high
 company values.

---
 src/core/bitmath_func.cpp | 28 +++++++++++++++++++++++++++-
 src/core/bitmath_func.hpp |  1 +
 2 files changed, 28 insertions(+), 1 deletion(-)

(limited to 'src/core')

diff --git a/src/core/bitmath_func.cpp b/src/core/bitmath_func.cpp
index 9f36ed9a8..53139308a 100644
--- a/src/core/bitmath_func.cpp
+++ b/src/core/bitmath_func.cpp
@@ -25,7 +25,7 @@ const uint8 _ffb_64[64] = {
  * way further. If no bit is set return 0.
  *
  * @param x The value to search
- * @param The position of the first bit set
+ * @return The position of the first bit set
  */
 uint8 FindFirstBit(uint32 x)
 {
@@ -43,3 +43,29 @@ uint8 FindFirstBit(uint32 x)
 
 	return pos;
 }
+
+/**
+ * Search the last set bit in a 32 bit variable.
+ *
+ * This algorithm is a static implementation of a log
+ * conguence search algorithm. It checks the first half
+ * if there is a bit set search there further. And this
+ * way further. If no bit is set return 0.
+ *
+ * @param x The value to search
+ * @return The position of the last bit set
+ */
+uint8 FindLastBit(uint32 x)
+{
+	if (x == 0) return 0;
+
+	uint8 pos = 0;
+
+	if ((x & 0xffff0000) != 0) { x >>= 16; pos += 16; }
+	if ((x & 0x0000ff00) != 0) { x >>= 8;  pos += 8;  }
+	if ((x & 0x000000f0) != 0) { x >>= 4;  pos += 4;  }
+	if ((x & 0x0000000c) != 0) { x >>= 2;  pos += 2;  }
+	if ((x & 0x00000002) != 0) { pos += 1; }
+
+	return pos;
+}
diff --git a/src/core/bitmath_func.hpp b/src/core/bitmath_func.hpp
index 1877f003e..f4c6ff0bc 100644
--- a/src/core/bitmath_func.hpp
+++ b/src/core/bitmath_func.hpp
@@ -211,6 +211,7 @@ static inline uint8 FindFirstBit2x64(const int value)
 }
 
 uint8 FindFirstBit(uint32 x);
+uint8 FindLastBit(uint32 x);
 
 /**
  * Clear the first bit in an integer.
-- 
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