}
}
+/*
+ * lfsr_next does the following:
+ *
+ * a. Return if the number of max values has been exceeded.
+ * 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;
-
- repeat = fl->num_vals % fl->cycle_length;
- if (repeat == 0)
- spin = fl->spin + 1;
- else
- spin = fl->spin;
+ unsigned int spin = fl->spin;
- if (fl->num_vals > fl->max_val)
+ if (fl->num_vals++ > fl->max_val)
return 1;
- fl->num_vals++;
-
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;
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++) {
break;
}
}
+ fl->cached_cycle_length = fl->cycle_length;
return 0;
}