[PATCH v4 1/5] lib/bitmap: add bitmap_{set,get}_value()

[Alexander Potapenko <glider@google.com>]

From: Syed Nayyar Waris <syednwaris@gmail.com>

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@arndb.de>
Signed-off-by: Syed Nayyar Waris <syednwaris@gmail.com>
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/lkml/fe12eedf3666f4af5138de0e70b67a07c7f40338.1592224129.git.syednwaris@gmail.com/
Suggested-by: Yury Norov <yury.norov@gmail.com>
Co-developed-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>

---
v4:
 - Address comments by Andy Shevchenko and Yury Norov:
   - prevent passing values >= 64 to GENMASK()
   - fix commit authorship
   - change comments
   - check for unlikely(nbits==0)
   - drop unnecessary const declarations
   - fix kernel-doc comments
   - rename bitmap_{get,set}_value() to bitmap_{read,write}()
---
 include/linux/bitmap.h | 60 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 03644237e1efb..bc21c09a2e038 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_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
  *
  * Note, bitmap_zero() and bitmap_fill() operate over the region of
  * unsigned longs, that is, bits behind bitmap till the unsigned long
@@ -583,6 +587,33 @@ static inline unsigned long bitmap_get_value8(const unsigned long *map,
 	return (map[index] >> offset) & 0xFF;
 }
 
+/**
+ * bitmap_read - read 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, up to BITS_PER_LONG
+ *
+ * Returns: value of nbits located at the @start bit offset within the @map
+ * memory region.
+ */
+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;
+	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 +630,35 @@ static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
 	map[index] |= value << offset;
 }
 
+/**
+ * bitmap_write - write 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, up to BITS_PER_LONG
+ */
+static inline void bitmap_write(unsigned long *map,
+				unsigned long value,
+				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;
+
+	if (unlikely(!nbits))
+		return;
+	value &= GENMASK(nbits - 1, 0);
+	if (space >= nbits) {
+		map[index] &= ~(GENMASK(nbits - 1, 0) << 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 */
-- 
2.41.0.487.g6d72f3e995-goog