Changes:
1. Verification now works properly and reports for which value it fails
2. Fix a mishandling of spin incrementation which led to multiple
calculation of the same values
Signed-off-by: Alex Pyrgiotis <apyrgio@xxxxxxxx>
diff --git a/lib/lfsr.c b/lib/lfsr.c
index 4c15c62..b10ba7a 100644
--- a/lib/lfsr.c
+++ b/lib/lfsr.c
@@ -112,26 +112,36 @@ static inline void __lfsr_next(struct fio_lfsr *fl, unsigned int spin)
* lfsr_next does the following:
*
* a. Return if the number of max values has been exceeded.
- * b. Check if the next iteration(s) produce a cycle (due to spin) and add "1"
- * where necessary.
- * c. Calculate the next value and return.
+ * b. Check if we have a spin value that produces a repeating subsequence.
+ * This is previously calculated in `prepare_spin` and cycle_length should
+ * be > 0. If we do have such a spin:
+ *
+ * i. Decrement the calculated cycle.
+ * ii. If it reaches zero, add "+1" to the spin and reset the cycle_length
+ * (we have it cached in the struct fio_lfsr)
+ *
+ * In either case, continue with the calculation of the next value.
+ * c. Check if the calculated value exceeds the desirable range. In this case,
+ * go back to b, else return.
*/
int lfsr_next(struct fio_lfsr *fl, uint64_t *off, uint64_t last)
{
- int repeat;
- unsigned int spin;
+ unsigned int spin = fl->spin;
if (fl->num_vals++ > fl->max_val)
return 1;
- repeat = fl->num_vals % fl->cycle_length;
- if (repeat == 0)
- spin = fl->spin + 1;
- else
- spin = fl->spin;
-
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;
+ }
+ }
__lfsr_next(fl, spin);
+check: ;
} while (fl->last_val > fl->max_val);
*off = fl->last_val;
@@ -189,7 +199,7 @@ int prepare_spin(struct fio_lfsr *fl, unsigned int spin)
x = max / (spin + 1);
y = max % (spin + 1);
- fl->cycle_length = max; /* This is the expected cycle */
+ fl->cycle_length = 0; /* No cycle occurs, other than the expected */
fl->spin = spin;
for (i = 1; i <= spin; i++) {
@@ -198,6 +208,7 @@ int prepare_spin(struct fio_lfsr *fl, unsigned int spin)
break;
}
}
+ fl->cached_cycle_length = fl->cycle_length;
return 0;
}
diff --git a/lib/lfsr.h b/lib/lfsr.h
index bc16af9..187abf2 100644
--- a/lib/lfsr.h
+++ b/lib/lfsr.h
@@ -18,6 +18,7 @@ struct fio_lfsr {
uint64_t max_val;
uint64_t num_vals;
uint64_t cycle_length;
+ uint64_t cached_cycle_length;
unsigned int spin;
};
diff --git a/t/lfsr-test.c b/t/lfsr-test.c
index 193a7f9..d371087 100644
--- a/t/lfsr-test.c
+++ b/t/lfsr-test.c
@@ -94,13 +94,15 @@ int main(int argc, char *argv[])
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end);
fprintf(stderr, "finished.\n");
+
/* Check if all expected numbers within range have been calculated */
r = 0;
if (verify) {
fprintf(stderr, "Verifying results... ");
for (i = 0; i < numbers; i++) {
- if (*(uint8_t *)(v + 1) != 1) {
- fprintf(stderr, "failed.\n");
+ if (*(uint8_t *)(v + i) != 1) {
+ fprintf(stderr, "failed (%lu = %d).\n",
+ i, *(uint8_t *)(v + i));
r = 1;
break;
}
--
1.8.1.4
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