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SubjectPatch 1/23 - Bitmaps, Cpumasks and Nodemasks
P1.bitmap_comment - Document bitmap.c bit model.
Document the bitmap bit model, including handling of unused bits,
and operation preconditions and postconditions.

Index: 2.6.5.bitmap/lib/bitmap.c
===================================================================
--- 2.6.5.bitmap.orig/lib/bitmap.c 2004-04-05 02:00:15.000000000 -0700
+++ 2.6.5.bitmap/lib/bitmap.c 2004-04-05 02:50:25.000000000 -0700
@@ -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.
+ *
+ * Except for bitmap_complement, these operations 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.
+ */
+
#define MAX_BITMAP_BITS 512U /* for ia64 NR_CPUS maximum */

int bitmap_empty(const unsigned long *bitmap, int bits)

--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@sgi.com> 1.650.933.1373
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