From d56036a40edce5619d6e9346b1e9d34822ab1437 Mon Sep 17 00:00:00 2001 From: Alex Pyrgiotis Date: Tue, 27 Aug 2013 10:58:34 -0600 Subject: [PATCH] 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 Signed-off-by: Jens Axboe --- lib/lfsr.c | 29 +++++++++++++++++------------ 1 file changed, 17 insertions(+), 12 deletions(-) diff --git a/lib/lfsr.c b/lib/lfsr.c index b10ba7a7..927b2a10 100644 --- a/lib/lfsr.c +++ b/lib/lfsr.c @@ -87,7 +87,6 @@ static inline void __lfsr_next(struct fio_lfsr *fl, unsigned int spin) * 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 @@ static inline void __lfsr_next(struct fio_lfsr *fl, unsigned int spin) */ 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 @@ static uint8_t *find_lfsr(uint64_t size) { 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 @@ int prepare_spin(struct fio_lfsr *fl, unsigned int spin) } 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; } -- 2.25.1