The new bitmap function bitmap_cut() copies bits from source to
destination by removing the region specified by parameters first
and cut, and remapping the bits above the cut region by right
shifting them.
Signed-off-by: Stefano Brivio <sbrivio@xxxxxxxxxx>
---
include/linux/bitmap.h | 4 +++
lib/bitmap.c | 66 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 70 insertions(+)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 29fc933df3bf..e66cff371688 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -53,6 +53,7 @@
* bitmap_find_next_zero_area_off(buf, len, pos, n, mask) as above
* bitmap_shift_right(dst, src, n, nbits) *dst = *src >> n
* 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_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
@@ -130,6 +131,9 @@ extern void __bitmap_shift_right(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits);
extern void __bitmap_shift_left(unsigned long *dst, const unsigned long *src,
unsigned int shift, unsigned int nbits);
+extern void bitmap_cut(unsigned long *dst, const unsigned long *src,
+ unsigned int first, unsigned int cut,
+ unsigned int nbits);
extern int __bitmap_and(unsigned long *dst, const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int nbits);
extern void __bitmap_or(unsigned long *dst, const unsigned long *bitmap1,
diff --git a/lib/bitmap.c b/lib/bitmap.c
index f9e834841e94..90ac4f413275 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -168,6 +168,72 @@ void __bitmap_shift_left(unsigned long *dst, const unsigned long *src,
}
EXPORT_SYMBOL(__bitmap_shift_left);
+/**
+ * bitmap_cut() - remove bit region from bitmap and right shift remaining bits
+ * @dst: destination bitmap, might overlap with src
+ * @src: source bitmap
+ * @first: start bit of region to be removed
+ * @cut: number of bits to remove
+ * @nbits: bitmap size, in bits
+ *
+ * Set the n-th bit of @dst iff the n-th bit of @src is set and
+ * n is less than @first, or the m-th bit of @src is set for any
+ * m such that @first <= n < nbits, and m = n + @cut.
+ *
+ * In pictures, example for a big-endian 32-bit architecture:
+ *
+ * @src:
+ * 31 63
+ * | |
+ * 10000000 11000001 11110010 00010101 10000000 11000001 01110010 00010101
+ * | | | |
+ * 16 14 0 32
+ *
+ * if @cut is 3, and @first is 14, bits 14-16 in @src are cut and @dst is:
+ *
+ * 31 63
+ * | |
+ * 10110000 00011000 00110010 00010101 00010000 00011000 00101110 01000010
+ * | | |
+ * 14 (bit 17 0 32
+ * from @src)
+ *
+ * Note that @dst and @src might overlap partially or entirely.
+ *
+ * This is implemented in the obvious way, with a shift and carry
+ * step for each moved bit. Optimisation is left as an exercise
+ * for the compiler.
+ */
+void bitmap_cut(unsigned long *dst, const unsigned long *src,
+ unsigned int first, unsigned int cut, unsigned int nbits)
+{
+ unsigned int len = BITS_TO_LONGS(nbits);
+ unsigned long keep = 0, carry;
+ int i;
+
+ memmove(dst, src, len * sizeof(*dst));
+
+ if (first % BITS_PER_LONG) {
+ keep = src[first / BITS_PER_LONG] &
+ (~0UL >> (BITS_PER_LONG - first % BITS_PER_LONG));
+ }
+
+ while (cut--) {
+ for (i = first / BITS_PER_LONG; i < len; i++) {
+ if (i < len - 1)
+ carry = dst[i + 1] & 1UL;
+ else
+ carry = 0;
+
+ dst[i] = (dst[i] >> 1) | (carry << (BITS_PER_LONG - 1));
+ }
+ }
+
+ dst[first / BITS_PER_LONG] &= ~0UL << (first % BITS_PER_LONG);
+ dst[first / BITS_PER_LONG] |= keep;
+}
+EXPORT_SYMBOL(bitmap_cut);
+
int __bitmap_and(unsigned long *dst, const unsigned long *bitmap1,
const unsigned long *bitmap2, unsigned int bits)
{
--
2.20.1
