bitvec_read_field(): optimize by expanding bytenum_from_bitnum()
The bitvec_read_field() is used in performance critical places,
such as the CSN.1 decoder in osmo-pcu. Thus the less conditional
statements we have in the parsing loop, the better.
The bitvec_get_bit_pos() alone is quite a complex function, which
does check the boundaries and even supports the L/H syntax. Even
if it gets inlined by the compiler, we don't really want to run
redundant checks and run bitval2mask() on each iteration.
Change-Id: I438fc82d33ab2edbabd4215ec7bc46afb07d50ab
diff --git a/src/bitvec.c b/src/bitvec.c
index 2303a0d..13deeff 100644
--- a/src/bitvec.c
+++ b/src/bitvec.c
@@ -491,8 +491,10 @@
errno = 0;
for (i = 0; i < len; i++) {
- int bit = bitvec_get_bit_pos((const struct bitvec *)bv, bv->cur_bit);
- if (bit)
+ unsigned int bytenum = bytenum_from_bitnum(bv->cur_bit);
+ unsigned int bitnum = 7 - (bv->cur_bit % 8);
+
+ if (bv->data[bytenum] & (1 << bitnum))
ui |= ((uint64_t)1 << (len - i - 1));
bv->cur_bit++;
}