LFSR: Do not ignore returning the seed
Fix a situation where we would spin prematurely and would hop over the
seed value.
Also, add some more comments to the code.
Signed-off-by: Alex Pyrgiotis <apyrgio@grnet.gr>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/lib/lfsr.c b/lib/lfsr.c
index b10ba7a..927b2a1 100644
--- a/lib/lfsr.c
+++ b/lib/lfsr.c
@@ -87,7 +87,6 @@
* this switch.
*/
switch (spin) {
- case 16: __LFSR_NEXT(fl, fl->last_val);
case 15: __LFSR_NEXT(fl, fl->last_val);
case 14: __LFSR_NEXT(fl, fl->last_val);
case 13: __LFSR_NEXT(fl, fl->last_val);
@@ -126,21 +125,16 @@
*/
int lfsr_next(struct fio_lfsr *fl, uint64_t *off, uint64_t last)
{
- unsigned int spin = fl->spin;
-
if (fl->num_vals++ > fl->max_val)
return 1;
do {
- if (fl->cycle_length) {
- fl->cycle_length--;
- if (!fl->cycle_length) {
- __lfsr_next(fl, fl->spin + 1);
- fl->cycle_length = fl->cached_cycle_length;
- goto check;
- }
+ if (fl->cycle_length && !--fl->cycle_length) {
+ __lfsr_next(fl, fl->spin + 1);
+ fl->cycle_length = fl->cached_cycle_length;
+ goto check;
}
- __lfsr_next(fl, spin);
+ __lfsr_next(fl, fl->spin);
check: ;
} while (fl->last_val > fl->max_val);
@@ -163,8 +157,13 @@
{
int i;
+ /*
+ * For an LFSR, there is always a prohibited state (all ones).
+ * Thus, if we need to find the proper LFSR for our size, we must take that
+ * into account.
+ */
for (i = 3; i < 64; i++)
- if ((1UL << i) > size) /* TODO: Explain why. */
+ if ((1UL << i) > size)
return taps[i];
return NULL;
@@ -210,6 +209,12 @@
}
fl->cached_cycle_length = fl->cycle_length;
+ /*
+ * Increment cycle length for the first time only since the stored value
+ * will not be printed otherwise.
+ */
+ fl->cycle_length++;
+
return 0;
}