From b7f0e00c65068b4f6920f359d3e652a951c7b5b9 Mon Sep 17 00:00:00 2001
From: David Given <dg@cowlark.com>
Date: Sat, 21 Jan 2017 20:50:57 +0100
Subject: [PATCH] Add a function for finding the first unset bit.

---
 modules/src/data/bitmap.c | 28 +++++++++++++++++++++++++++-
 modules/src/data/bitmap.h |  1 +
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/modules/src/data/bitmap.c b/modules/src/data/bitmap.c
index 363d22d49..d47684d9d 100644
--- a/modules/src/data/bitmap.c
+++ b/modules/src/data/bitmap.c
@@ -1,6 +1,7 @@
 #include <stdlib.h>
 #include <stdbool.h>
 #include <strings.h>
+#include <limits.h>
 #include <assert.h>
 #include "bitmap.h"
 
@@ -35,7 +36,7 @@ int bitmap_findfirst(unsigned int* bitmap, int size)
 	{
 		unsigned int w = bitmap[word];
 		if (w)
-			return ffs(w) + word*BITS_PER_WORD;
+			return (ffs(w)-1) + word*BITS_PER_WORD;
 	}
 
 	return -1;
@@ -59,3 +60,28 @@ void bitmap_or(unsigned int* dest, int size, unsigned int* src)
 		dest[word] |= src[word];
 }
 
+int bitmap_find_unset_bit(unsigned int* bitmap, int size)
+{
+	int word;
+	int words = ((size-1) / BITS_PER_WORD) + 1;
+
+	for (word=0; word<words; word++)
+	{
+		unsigned int w = bitmap[word];
+		if (w != UINT_MAX)
+		{
+			int mask = 1;
+			int pos = 0;
+
+			while (w & mask)
+			{
+				mask <<= 1;
+				pos++;
+			}
+
+			return (word*BITS_PER_WORD) + pos;
+		}
+	}
+
+	return -1;
+}
diff --git a/modules/src/data/bitmap.h b/modules/src/data/bitmap.h
index d3bd23603..999bb7ecb 100644
--- a/modules/src/data/bitmap.h
+++ b/modules/src/data/bitmap.h
@@ -8,6 +8,7 @@ extern bool bitmap_get(unsigned int* bitmap, int size, int bit);
 extern int bitmap_findfirst(unsigned int* bitmap, int size);
 extern void bitmap_and(unsigned int* dest, int size, unsigned int* src);
 extern void bitmap_or(unsigned int* dest, int size, unsigned int* src);
+extern int bitmap_find_unset_bit(unsigned int* bitmap, int size);
 
 #define BITS_PER_WORD (sizeof(unsigned int)*8)
 #define WORDS_FOR_BITMAP_SIZE(n) (((n-1) / BITS_PER_WORD) + 1)
-- 
2.34.1