[dm-devel] [PATCH v2] lib/memweight.c: open codes bitmap_weight()

[Denis Efremov]

This patch open codes the bitmap_weight() call. The direct
invocation of hweight_long() allows to remove the BUG_ON and
excessive "longs to bits, bits to longs" conversion.

BUG_ON was required to check that bitmap_weight() will return
a correct value, i.e. the computed weight will fit the int type
of the return value. With this patch memweight() controls the
computation directly with size_t type everywhere. Thus, the BUG_ON
becomes unnecessary.

Total size reduced:
./scripts/bloat-o-meter lib/memweight.o.old lib/memweight.o.new
add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-10 (-10)
Function                                     old     new   delta
memweight                                    162     152     -10

Co-developed-by: Erdem Tumurov <erdemus at gmail.com>
Signed-off-by: Erdem Tumurov <erdemus at gmail.com>
Co-developed-by: Vladimir Shelekhov <vshel at iis.nsk.su>
Signed-off-by: Vladimir Shelekhov <vshel at iis.nsk.su>
Signed-off-by: Denis Efremov <efremov at ispras.ru>
---
 lib/memweight.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lib/memweight.c b/lib/memweight.c
index 94dd72ccaa7f..f050b2b4c5e2 100644
--- a/lib/memweight.c
+++ b/lib/memweight.c
@@ -20,11 +20,13 @@ size_t memweight(const void *ptr, size_t bytes)
 
 	longs = bytes / sizeof(long);
 	if (longs) {
-		BUG_ON(longs >= INT_MAX / BITS_PER_LONG);
-		ret += bitmap_weight((unsigned long *)bitmap,
-				longs * BITS_PER_LONG);
+		const unsigned long *bitmap_long =
+			(const unsigned long *)bitmap;
+
 		bytes -= longs * sizeof(long);
-		bitmap += longs * sizeof(long);
+		for (; longs > 0; longs--, bitmap_long++)
+			ret += hweight_long(*bitmap_long);
+		bitmap = (const unsigned char *)bitmap_long;
 	}
 	/*
 	 * The reason that this last loop is distinct from the preceding
-- 
2.21.0