On Fri, Oct 06, 2023 at 03:45:25PM +0200, Alexander Potapenko wrote:

From: Syed Nayyar Waris <redacted>

The two new functions allow reading/writing values of length up to
BITS_PER_LONG bits at arbitrary position in the bitmap.

The code was taken from "bitops: Introduce the for_each_set_clump macro"
by Syed Nayyar Waris with a number of changes and simplifications:
 - instead of using roundup(), which adds an unnecessary dependency
   on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
 - indentation is reduced by not using else-clauses (suggested by
   checkpatch for bitmap_get_value());
 - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
   and bitmap_write();
 - some redundant computations are omitted.

...

v6:
 - As suggested by Yury Norov, do not require bitmap_read(..., 0) to
   return 0.

Hmm... See below.

...

  *  bitmap_to_arr32(buf, src, nbits)            Copy nbits from buf to u32[] dst
  *  bitmap_to_arr64(buf, src, nbits)            Copy nbits from buf to u64[] dst

With the grouping as below I would add a blank line here. But was the intention
to group _arrXX() to these groups?

  *  bitmap_get_value8(map, start)               Get 8bit value from map at start
+ *  bitmap_read(map, start, nbits)              Read an nbits-sized value from
+ *                                              map at start
  *  bitmap_set_value8(map, value, start)        Set 8bit value to map at start
+ *  bitmap_write(map, value, start, nbits)      Write an nbits-sized value to
+ *                                              map at start

...

+static inline unsigned long bitmap_read(const unsigned long *map,
+					unsigned long start,
+					unsigned long nbits)
+{
+	size_t index = BIT_WORD(start);
+	unsigned long offset = start % BITS_PER_LONG;
+	unsigned long space = BITS_PER_LONG - offset;
+	unsigned long value_low, value_high;

+	if (unlikely(!nbits))
+		return 0;

Hmm... I didn't get was the comment to add or to remove these checks?

+	if (space >= nbits)
+		return (map[index] >> offset) & GENMASK(nbits - 1, 0);

And don't you want to replace this GENMASK() as well?

+	value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
+	value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
+	return (value_low >> offset) | (value_high << space);
+}

-- 
With Best Regards,
Andy Shevchenko



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