[PATCH 17/18] bcache: make bset_search_tree() be more understandable

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The purpose of following code in bset_search_tree() is to avoid a branch
instruction,
 994         if (likely(f->exponent != 127))
 995                 n = j * 2 + (((unsigned int)
 996                               (f->mantissa -
 997                                bfloat_mantissa(search, f))) >> 31);
 998         else
 999                 n = (bkey_cmp(tree_to_bkey(t, j), search) > 0)
1000                         ? j * 2
1001                         : j * 2 + 1;

This piece of code is not very clear to understand, even when I tried to
add code comment for it, I made mistake. This patch removes the implict
bit operation and uses explicit branch to calculate next location in
binary tree search.

Signed-off-by: Coly Li <colyli@xxxxxxx>
---
 drivers/md/bcache/bset.c | 17 +++--------------
 1 file changed, 3 insertions(+), 14 deletions(-)

diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index eedaf0f3e3f0..32e2e4d8fa6c 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -965,21 +965,10 @@ static struct bset_search_iter bset_search_tree(struct bset_tree *t,
 		j = n;
 		f = &t->tree[j];
 
-		/*
-		 * Similar bit trick, use subtract operation to avoid a branch
-		 * instruction.
-		 *
-		 * n = (f->mantissa > bfloat_mantissa())
-		 *	? j * 2
-		 *	: j * 2 + 1;
-		 *
-		 * We need to subtract 1 from f->mantissa for the sign bit trick
-		 * to work  - that's done in make_bfloat()
-		 */
 		if (likely(f->exponent != 127))
-			n = j * 2 + (((unsigned int)
-				      (f->mantissa -
-				       bfloat_mantissa(search, f))) >> 31);
+			n = (f->mantissa >= bfloat_mantissa(search, f))
+				? j * 2
+				: j * 2 + 1;
 		else
 			n = (bkey_cmp(tree_to_bkey(t, j), search) > 0)
 				? j * 2
-- 
2.16.4




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