[PATCH] cpumask: bitmap cleanup preparation for cpumask overhaul

From: Paul Jackson <pj@sgi.com>

Document the bitmap bit model and handling of unused bits.

Tighten up bitmap so it does not generate nonzero bits in the unused tail if
it is not given any on input.

Add intersects, subset, xor and andnot operators.  Change bitmap_complement to
take two operands.

Add a couple of missing 'const' qualifiers on bitops test_bit and bitmap_equal
args.

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 81 insertions, 6 deletions

diff --git a/lib/bitmap.c b/lib/bitmap.c
index 779d30365e4617..a96433e3710291 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -12,6 +12,26 @@
 #include <asm/bitops.h>
 #include <asm/uaccess.h>
 
+/*
+ * bitmaps provide an array of bits, implemented using an an
+ * array of unsigned longs.  The number of valid bits in a
+ * given bitmap need not be an exact multiple of BITS_PER_LONG.
+ *
+ * The possible unused bits in the last, partially used word
+ * of a bitmap are 'don't care'.  The implementation makes
+ * no particular effort to keep them zero.  It ensures that
+ * their value will not affect the results of any operation.
+ * The bitmap operations that return Boolean (bitmap_empty,
+ * for example) or scalar (bitmap_weight, for example) results
+ * carefully filter out these unused bits from impacting their
+ * results.
+ *
+ * These operations actually hold to a slightly stronger rule:
+ * if you don't input any bitmaps to these ops that have some
+ * unused bits set, then they won't output any set unused bits
+ * in output bitmaps.
+ */
+
 int bitmap_empty(const unsigned long *bitmap, int bits)
 {
 	int k, lim = bits/BITS_PER_LONG;
@@ -43,7 +63,7 @@ int bitmap_full(const unsigned long *bitmap, int bits)
 EXPORT_SYMBOL(bitmap_full);
 
 int bitmap_equal(const unsigned long *bitmap1,
-		unsigned long *bitmap2, int bits)
+		const unsigned long *bitmap2, int bits)
 {
 	int k, lim = bits/BITS_PER_LONG;
 	for (k = 0; k < lim; ++k)
@@ -59,13 +79,14 @@ int bitmap_equal(const unsigned long *bitmap1,
 }
 EXPORT_SYMBOL(bitmap_equal);
 
-void bitmap_complement(unsigned long *bitmap, int bits)
+void bitmap_complement(unsigned long *dst, const unsigned long *src, int bits)
 {
-	int k;
-	int nr = BITS_TO_LONGS(bits);
+	int k, lim = bits/BITS_PER_LONG;
+	for (k = 0; k < lim; ++k)
+		dst[k] = ~src[k];
 
-	for (k = 0; k < nr; ++k)
-		bitmap[k] = ~bitmap[k];
+	if (bits % BITS_PER_LONG)
+		dst[k] = ~src[k] & ((1UL << (bits % BITS_PER_LONG)) - 1);
 }
 EXPORT_SYMBOL(bitmap_complement);
 
@@ -173,6 +194,60 @@ void bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
 }
 EXPORT_SYMBOL(bitmap_or);
 
+void bitmap_xor(unsigned long *dst, const unsigned long *bitmap1,
+				const unsigned long *bitmap2, int bits)
+{
+	int k;
+	int nr = BITS_TO_LONGS(bits);
+
+	for (k = 0; k < nr; k++)
+		dst[k] = bitmap1[k] ^ bitmap2[k];
+}
+EXPORT_SYMBOL(bitmap_xor);
+
+void bitmap_andnot(unsigned long *dst, const unsigned long *bitmap1,
+				const unsigned long *bitmap2, int bits)
+{
+	int k;
+	int nr = BITS_TO_LONGS(bits);
+
+	for (k = 0; k < nr; k++)
+		dst[k] = bitmap1[k] & ~bitmap2[k];
+}
+EXPORT_SYMBOL(bitmap_andnot);
+
+int bitmap_intersects(const unsigned long *bitmap1,
+				const unsigned long *bitmap2, int bits)
+{
+	int k, lim = bits/BITS_PER_LONG;
+	for (k = 0; k < lim; ++k)
+		if (bitmap1[k] & bitmap2[k])
+			return 1;
+
+	if (bits % BITS_PER_LONG)
+		if ((bitmap1[k] & bitmap2[k]) &
+				((1UL << (bits % BITS_PER_LONG)) - 1))
+			return 1;
+	return 0;
+}
+EXPORT_SYMBOL(bitmap_intersects);
+
+int bitmap_subset(const unsigned long *bitmap1,
+				const unsigned long *bitmap2, int bits)
+{
+	int k, lim = bits/BITS_PER_LONG;
+	for (k = 0; k < lim; ++k)
+		if (bitmap1[k] & ~bitmap2[k])
+			return 0;
+
+	if (bits % BITS_PER_LONG)
+		if ((bitmap1[k] & ~bitmap2[k]) &
+				((1UL << (bits % BITS_PER_LONG)) - 1))
+			return 0;
+	return 1;
+}
+EXPORT_SYMBOL(bitmap_subset);
+
 #if BITS_PER_LONG == 32
 int bitmap_weight(const unsigned long *bitmap, int bits)
 {