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 <[email protected]> --- 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
