From 7078f3af87a1898999f8e2bbfef6c3895d5f7316 Mon Sep 17 00:00:00 2001
From: Holger Schemel <info@artsoft.org>
Date: Wed, 17 May 2023 12:29:18 +0200
Subject: [PATCH] moved code to count bits to separate function

---
 src/editor.c       | 15 +++------------
 src/libgame/misc.c | 25 +++++++++++++++++++++++++
 src/libgame/misc.h |  1 +
 3 files changed, 29 insertions(+), 12 deletions(-)

diff --git a/src/editor.c b/src/editor.c
index d4e2bc8e..25edbb4b 100644
--- a/src/editor.c
+++ b/src/editor.c
@@ -12054,19 +12054,10 @@ static boolean isHiresDrawElement(int element)
 
 static int numHiresTiles(int element)
 {
-  if (!IS_MM_WALL(element))
-    return 1;
-
-  int bits = MM_WALL_BITS(element);
-  int num_bits = 0;
-
-  while (bits)
-  {
-    bits &= bits - 1;
-    num_bits++;
-  }
+  if (IS_MM_WALL(element))
+    return get_number_of_bits(MM_WALL_BITS(element));
 
-  return num_bits;
+  return 1;
 }
 
 static void SetDrawModeHiRes(int element)
diff --git a/src/libgame/misc.c b/src/libgame/misc.c
index a76bba56..02358aa2 100644
--- a/src/libgame/misc.c
+++ b/src/libgame/misc.c
@@ -1682,6 +1682,31 @@ void swap_number_pairs(int *x1, int *y1, int *x2, int *y2)
   *y2 = help_y;
 }
 
+int get_number_of_bits(int bits)
+{
+  /*
+    Counting bits set, Brian Kernighan's way
+
+    Brian Kernighan's method goes through as many iterations as there are set
+    bits. So if we have a 32-bit word with only the high bit set, then it will
+    only go once through the loop.
+
+    Published in 1988, the C Programming Language 2nd Ed. (by Brian W. Kernighan
+    and Dennis M. Ritchie) mentions this in exercise 2-9.
+    First published by Peter Wegner in CACM 3 (1960), 322.
+  */
+
+  int num_bits = 0;
+
+  while (bits)
+  {
+    bits &= bits - 1;	// clear the least significant bit set
+    num_bits++;
+  }
+
+  return num_bits;
+}
+
 /* the "put" variants of the following file access functions check for the file
    pointer being != NULL and return the number of bytes they have or would have
    written; this allows for chunk writing functions to first determine the size
diff --git a/src/libgame/misc.h b/src/libgame/misc.h
index c8e00c84..7097e968 100644
--- a/src/libgame/misc.h
+++ b/src/libgame/misc.h
@@ -203,6 +203,7 @@ void clear_mem(void *, unsigned int);
 
 void swap_numbers(int *, int *);
 void swap_number_pairs(int *, int *, int *, int *);
+int get_number_of_bits(int);
 
 int getFile8BitInteger(File *);
 int putFile8BitInteger(FILE *, int);
-- 
2.34.1