***
In the lookahead logic, let's say after the Right-Shift-And operation to check
for contiguity, we hit case
http://code.dpdk.org/dpdk/latest/source/lib/eal/common/eal_common_fbarray.c#L235
/* if first bit is not set, we've lost the run */
if ((lookahead_msk & 1) == 0) {
/*
* we've scanned this far, so we know there are
* no runs in the space we've lookahead-scanned
* as well, so skip that on next iteration.
*/
ignore_msk = ~((1ULL << need) - 1);
msk_idx = lookahead_idx;
break;
}
lets say for mask size of 64 bits : in msk_idx 4 we need 4 consecutive
bits.
let need = 4.
lets say some of the bits starting from LSB are xx11011.
Operating on the inverted mask for better clarity. RSA - RightShiftAnd,
xx -- don't-care bits before
This condition could hit if there aren't "need" number of contiguous
bits starting from LSB.
But, that doesn't necessarily mean there aren't "need" number of such
bits elsewhere in the same lookahead_idx.
We seem to be ignoring "need" number of bits starting from the LSB for
the next iteration.
Due to ignore_mask we might end losing some bits.
/* if we have an ignore mask, ignore once */
if (ignore_msk) {
cur_msk &= ignore_msk;
ignore_msk = 0;
}
e.g.
lookahead_msk before RSA logic : xx11100 , need = 4, 2 bits lost
lookahead_msk before RSA logic : xx11011, need = 4, 1 bit lost
lookahead_msk before RSA logic : xx11110, need = 4, 3 bits lost
NB : To understand the number of bits lost, look at need; that's the number of
bits (starting from LSB) that's cleared to zero before the next iteration.
***
Vipin P R (2):
Memory Allocation: Fixes ignore_msk during find_next_n() in fb_array
library
Memory Allocation: Alternative fix for ignore_msk during find_next_n()
in fb_array library
lib/eal/common/eal_common_fbarray.c | 26 +++++++++++++++++++++++---
1 file changed, 23 insertions(+), 3 deletions(-)
--
2.7.4
