[PATCH v5 3/5] lib/bitmap: Introduce bitmap_scatter() and bitmap_gather() helpers

Herve Codina
2024-02-29T14:16:17Z

From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

These helpers scatters or gathers a bitmap with the help of the mask
position bits parameter.

bitmap_scatter() does the following:
src: 0000000001011010
||||||
+------+|||||
| +----+||||
| |+----+|||
| || +-+||
| || | ||
mask: ...v..vv...v..vv
...0..11...0..10
dst: 0000001100000010

and bitmap_gather() performs this one:
mask: ...v..vv...v..vv
src: 0000001100000010
^ ^^ ^ 0
| || | 10
| || > 010
| |+--> 1010
| +--> 11010
+----> 011010
dst: 0000000000011010

bitmap_gather() can the seen as the reverse bitmap_scatter() operation.

The original work was done by Andy Shevchenko.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/lkml/20230926052007.3917389-3-andriy.shevchenko@linux.intel.com/
Co-developed-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Herve Codina <herve.codina@bootlin.com>
---
include/linux/bitmap.h | 101 +++++++++++++++++++++++++++++++++++++++++
lib/test_bitmap.c | 42 +++++++++++++++++
2 files changed, 143 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 99451431e4d6..6d3f6ff1b4d6 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -62,6 +62,8 @@ struct device;
* bitmap_shift_left(dst, src, n, nbits) *dst = *src << n
* bitmap_cut(dst, src, first, n, nbits) Cut n bits from first, copy rest
* bitmap_replace(dst, old, new, mask, nbits) *dst = (*old & ~(*mask)) | (*new & *mask)
+ * bitmap_scatter(dst, src, mask, nbits) *dst = map(dense, sparse)(src)
+ * bitmap_gather(dst, src, mask, nbits) *dst = map(sparse, dense)(src)
* bitmap_remap(dst, src, old, new, nbits) *dst = map(old, new)(src)
* bitmap_bitremap(oldbit, old, new, nbits) newbit = map(old, new)(oldbit)
* bitmap_onto(dst, orig, relmap, nbits) *dst = orig relative to relmap
@@ -487,6 +489,105 @@ static inline void bitmap_replace(unsigned long *dst,
__bitmap_replace(dst, old, new, mask, nbits);
}

+/**
+ * bitmap_scatter - Scatter a bitmap according to the given mask
+ * @dst: scattered bitmap
+ * @src: gathered bitmap
+ * @mask: mask representing bits to assign to in the scattered bitmap
+ * @nbits: number of bits in each of these bitmaps
+ *
+ * Scatters bitmap with sequential bits according to the given @mask.
+ *
+ * Example:
+ * If @src bitmap = 0x005a, with @mask = 0x1313, @dst will be 0x0302.
+ *
+ * Or in binary form
+ * @src @mask @dst
+ * 0000000001011010 0001001100010011 0000001100000010
+ *
+ * (Bits 0, 1, 2, 3, 4, 5 are copied to the bits 0, 1, 4, 8, 9, 12)
+ *
+ * A more 'visual' description of the operation:
+ * src: 0000000001011010
+ * ||||||
+ * +------+|||||
+ * | +----+||||
+ * | |+----+|||
+ * | || +-+||
+ * | || | ||
+ * mask: ...v..vv...v..vv
+ * ...0..11...0..10
+ * dst: 0000001100000010
+ *
+ * A relationship exists between bitmap_scatter() and bitmap_gather().
+ * bitmap_gather() can be seen as the 'reverse' bitmap_scatter() operation.
+ * See bitmap_scatter() for details related to this relationship.
+ */
+static inline void bitmap_scatter(unsigned long *dst, const unsigned long *src,
+ const unsigned long *mask, unsigned int nbits)
+{
+ unsigned int n = 0;
+ unsigned int bit;
+
+ bitmap_zero(dst, nbits);
+
+ for_each_set_bit(bit, mask, nbits)
+ __assign_bit(bit, dst, test_bit(n++, src));
+}
+
+/**
+ * bitmap_gather - Gather a bitmap according to given mask
+ * @dst: gathered bitmap
+ * @src: scattered bitmap
+ * @mask: mask representing bits to extract from in the scattered bitmap
+ * @nbits: number of bits in each of these bitmaps
+ *
+ * Gathers bitmap with sparse bits according to the given @mask.
+ *
+ * Example:
+ * If @src bitmap = 0x0302, with @mask = 0x1313, @dst will be 0x001a.
+ *
+ * Or in binary form
+ * @src @mask @dst
+ * 0000001100000010 0001001100010011 0000000000011010
+ *
+ * (Bits 0, 1, 4, 8, 9, 12 are copied to the bits 0, 1, 2, 3, 4, 5)
+ *
+ * A more 'visual' description of the operation:
+ * mask: ...v..vv...v..vv
+ * src: 0000001100000010
+ * ^ ^^ ^ 0
+ * | || | 10
+ * | || > 010
+ * | |+--> 1010
+ * | +--> 11010
+ * +----> 011010
+ * dst: 0000000000011010
+ *
+ * A relationship exists between bitmap_gather() and bitmap_scatter(). See
+ * bitmap_scatter() for the bitmap scatter detailed operations.
+ * Suppose scattered computed using bitmap_scatter(scattered, src, mask, n).
+ * The operation bitmap_gather(result, scattered, mask, n) leads to a result
+ * equal or equivalent to src.
+ *
+ * The result can be 'equivalent' because bitmap_scatter() and bitmap_gather()
+ * are not bijective.
+ * The result and src values are equivalent in that sense that a call to
+ * bitmap_scatter(res, src, mask, n) and a call to bitmap_scatter(res, result,
+ * mask, n) will lead to the same res value.
+ */
+static inline void bitmap_gather(unsigned long *dst, const unsigned long *src,
+ const unsigned long *mask, unsigned int nbits)
+{
+ unsigned int n = 0;
+ unsigned int bit;
+
+ bitmap_zero(dst, nbits);
+
+ for_each_set_bit(bit, mask, nbits)
+ __assign_bit(n++, dst, test_bit(bit, src));
+}
+
static inline void bitmap_next_set_region(unsigned long *bitmap,
unsigned int *rs, unsigned int *re,
unsigned int end)
diff --git a/lib/test_bitmap.c b/lib/test_bitmap.c
index 65f22c2578b0..6b2b33579f56 100644
--- a/lib/test_bitmap.c
+++ b/lib/test_bitmap.c
@@ -380,6 +380,47 @@ static void __init test_replace(void)
expect_eq_bitmap(bmap, exp3_1_0, nbits);
}

+static const unsigned long sg_mask[] __initconst = {
+ BITMAP_FROM_U64(0x000000000000035aULL),
+};
+
+static const unsigned long sg_src[] __initconst = {
+ BITMAP_FROM_U64(0x0000000000000667ULL),
+};
+
+static const unsigned long sg_gather_exp[] __initconst = {
+ BITMAP_FROM_U64(0x0000000000000029ULL),
+};
+
+static const unsigned long sg_scatter_exp[] __initconst = {
+ BITMAP_FROM_U64(0x000000000000021aULL),
+};
+
+static void __init test_bitmap_sg(void)
+{
+ unsigned int nbits = 64;
+ DECLARE_BITMAP(bmap_gather, 100);
+ DECLARE_BITMAP(bmap_scatter, 100);
+ DECLARE_BITMAP(bmap_tmp, 100);
+ DECLARE_BITMAP(bmap_res, 100);
+
+ /* Simple gather call */
+ bitmap_zero(bmap_gather, 100);
+ bitmap_gather(bmap_gather, sg_src, sg_mask, nbits);
+ expect_eq_bitmap(sg_gather_exp, bmap_gather, nbits);
+
+ /* Simple scatter call */
+ bitmap_zero(bmap_scatter, 100);
+ bitmap_scatter(bmap_scatter, sg_src, sg_mask, nbits);
+ expect_eq_bitmap(sg_scatter_exp, bmap_scatter, nbits);
+
+ /* Scatter/gather relationship */
+ bitmap_zero(bmap_tmp, 100);
+ bitmap_gather(bmap_tmp, bmap_scatter, sg_mask, nbits);
+ bitmap_scatter(bmap_res, bmap_tmp, sg_mask, nbits);
+ expect_eq_bitmap(bmap_scatter, bmap_res, nbits);
+}
+
#define PARSE_TIME 0x1
#define NO_LEN 0x2

@@ -1252,6 +1293,7 @@ static void __init selftest(void)
test_copy();
test_bitmap_region();
test_replace();
+ test_bitmap_sg();
test_bitmap_arr32();
test_bitmap_arr64();
test_bitmap_parse();
--
2.43.0