From 12be876131ad76d0fb8e7d0fbff586ea1a0a693e Mon Sep 17 00:00:00 2001
From: maedhros <maedhros@openttd.org>
Date: Tue, 12 Jun 2007 22:13:49 +0000
Subject: [PATCH] (svn r10122) -Codechange: Add a CountBitsSet function and use
 it to replace some less efficient loops.

---
 src/economy.cpp     | 14 +++-----------
 src/functions.h     |  4 +++-
 src/misc.cpp        | 15 +++++++++++++++
 src/roadveh_cmd.cpp |  9 +--------
 4 files changed, 22 insertions(+), 20 deletions(-)

diff --git a/src/economy.cpp b/src/economy.cpp
index 64bcbe832e..967373c734 100644
--- a/src/economy.cpp
+++ b/src/economy.cpp
@@ -67,10 +67,7 @@ int64 CalculateCompanyValue(const Player* p)
 		uint num = 0;
 
 		FOR_ALL_STATIONS(st) {
-			if (st->owner == owner) {
-				uint facil = st->facilities;
-				do num += (facil&1); while (facil >>= 1);
-			}
+			if (st->owner == owner) num += CountBitsSet(st->facilities);
 		}
 
 		value = num * _price.station_value * 25;
@@ -144,10 +141,7 @@ int UpdateCompanyRatingAndValue(Player *p, bool update)
 		const Station* st;
 
 		FOR_ALL_STATIONS(st) {
-			if (st->owner == owner) {
-				int facil = st->facilities;
-				do num += facil&1; while (facil>>=1);
-			}
+			if (st->owner == owner) num += CountBitsSet(st->facilities);
 		}
 		_score_part[owner][SCORE_STATIONS] = num;
 	}
@@ -196,9 +190,7 @@ int UpdateCompanyRatingAndValue(Player *p, bool update)
 
 /* Generate score for variety of cargo */
 	{
-		uint cargo = p->cargo_types;
-		uint num = 0;
-		do num += cargo&1; while (cargo>>=1);
+		uint num = CountBitsSet(p->cargo_types);
 		_score_part[owner][SCORE_CARGO] = num;
 		if (update) p->cargo_types = 0;
 	}
diff --git a/src/functions.h b/src/functions.h
index 12cf9deb86..cc885917e2 100644
--- a/src/functions.h
+++ b/src/functions.h
@@ -147,9 +147,11 @@ Town *ClosestTownFromTile(TileIndex tile, uint threshold);
 void ChangeTownRating(Town *t, int add, int max);
 
 uint GetTownRadiusGroup(const Town* t, TileIndex tile);
-int FindFirstBit(uint32 x);
 void ShowHighscoreTable(int difficulty, int8 rank);
 
+int FindFirstBit(uint32 x);
+int CountBitsSet(uint32 value);
+
 void AfterLoadTown();
 void UpdatePatches();
 void AskExitGame();
diff --git a/src/misc.cpp b/src/misc.cpp
index 2dd2750d00..d143980c49 100644
--- a/src/misc.cpp
+++ b/src/misc.cpp
@@ -270,6 +270,21 @@ int FindFirstBit(uint32 value)
 	return i;
 }
 
+int CountBitsSet(uint32 value)
+{
+	int num;
+
+	/* This loop is only called once for every bit set by clearing the lowest
+	 * bit in each loop. The number of bits is therefore equal to the number of
+	 * times the loop was called. It was found at the following website:
+	 * http://graphics.stanford.edu/~seander/bithacks.html */
+
+	for (num = 0; value != 0; num++) {
+		value &= value - 1;
+	}
+
+	return num;
+}
 
 static void Save_NAME()
 {
diff --git a/src/roadveh_cmd.cpp b/src/roadveh_cmd.cpp
index b66483e70b..5c5e4023b1 100644
--- a/src/roadveh_cmd.cpp
+++ b/src/roadveh_cmd.cpp
@@ -1085,15 +1085,8 @@ static void RoadZPosAffectSpeed(Vehicle *v, byte old_z)
 
 static int PickRandomBit(uint bits)
 {
-	uint num = 0;
-	uint b = bits;
 	uint i;
-
-	do {
-		if (b & 1) num++;
-	} while (b >>= 1);
-
-	num = RandomRange(num);
+	uint num = RandomRange(CountBitsSet(bits));
 
 	for (i = 0; !(bits & 1) || (int)--num >= 0; bits >>= 1, i++) {}
 	return i;