[PATCH v3 1/5] lib/bitmap: add bitmap_{set,get}_value()

[Alexander Potapenko]

The two new functions allow setting/getting 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 couple of minor changes:
 - 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())

Cc: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Syed Nayyar Waris <syednwaris@xxxxxxxxx>
Signed-off-by: William Breathitt Gray <william.gray@xxxxxxxxxx>
Link: https://lore.kernel.org/lkml/fe12eedf3666f4af5138de0e70b67a07c7f40338.1592224129.git.syednwaris@xxxxxxxxx/
Suggested-by: Yury Norov <yury.norov@xxxxxxxxx>
Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
---
 include/linux/bitmap.h | 57 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 03644237e1efb..4559366084988 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -76,7 +76,11 @@ struct device;
  *  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
  *  bitmap_get_value8(map, start)               Get 8bit value from map at start
+ *  bitmap_get_value(map, start, nbits)         Get bit value of size 'nbits'
+ *                                              from map at start
  *  bitmap_set_value8(map, value, start)        Set 8bit value to map at start
+ *  bitmap_set_value(map, value, start, nbits)  Set bit value of size 'nbits'
+ *                                              of map at start
  *
  * Note, bitmap_zero() and bitmap_fill() operate over the region of
  * unsigned longs, that is, bits behind bitmap till the unsigned long
@@ -583,6 +587,31 @@ static inline unsigned long bitmap_get_value8(const unsigned long *map,
 	return (map[index] >> offset) & 0xFF;
 }
 
+/**
+ * bitmap_get_value - get a value of n-bits from the memory region
+ * @map: address to the bitmap memory region
+ * @start: bit offset of the n-bit value
+ * @nbits: size of value in bits
+ *
+ * Returns value of nbits located at the @start bit offset within the @map
+ * memory region.
+ */
+static inline unsigned long bitmap_get_value(const unsigned long *map,
+					     unsigned long start,
+					     unsigned long nbits)
+{
+	const size_t index = BIT_WORD(start);
+	const unsigned long offset = start % BITS_PER_LONG;
+	const unsigned long space = BITS_PER_LONG - offset;
+	unsigned long value_low, value_high;
+
+	if (space >= nbits)
+		return (map[index] >> offset) & GENMASK(nbits - 1, 0);
+	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);
+}
+
 /**
  * bitmap_set_value8 - set an 8-bit value within a memory region
  * @map: address to the bitmap memory region
@@ -599,6 +628,34 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
 	map[index] |= value << offset;
 }
 
+/**
+ * bitmap_set_value - set n-bit value within a memory region
+ * @map: address to the bitmap memory region
+ * @value: value of nbits
+ * @start: bit offset of the n-bit value
+ * @nbits: size of value in bits
+ */
+static inline void bitmap_set_value(unsigned long *map,
+				    unsigned long value,
+				    unsigned long start, unsigned long nbits)
+{
+	const size_t index = BIT_WORD(start);
+	const unsigned long offset = start % BITS_PER_LONG;
+	const unsigned long space = BITS_PER_LONG - offset;
+
+	value &= GENMASK(nbits - 1, 0);
+
+	if (space >= nbits) {
+		map[index] &= ~(GENMASK(nbits + offset - 1, offset));
+		map[index] |= value << offset;
+		return;
+	}
+	map[index] &= ~BITMAP_FIRST_WORD_MASK(start);
+	map[index] |= value << offset;
+	map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + nbits);
+	map[index + 1] |= (value >> space);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __LINUX_BITMAP_H */
-- 
2.41.0.255.g8b1d071c50-goog