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The following changes since commit c3a1b740381cb19e467c8588562bac4d6cbbb199:

  Fix skewed latencies for rate IOPS (2013-03-07 12:34:31 +0100)

are available in the git repository at:
  git://git.kernel.dk/fio.git master

Alex Pyrgiotis (2):
      Improve LFSR implementation
      Add a simple test for LFSR generator

Jens Axboe (1):
      lfsr: indent table

 Makefile      |    9 ++
 filesetup.c   |    2 +-
 lib/lfsr.c    |  421 +++++++++++++++++++++++++-------------------------------
 lib/lfsr.h    |   12 +-
 t/axmap.c     |    2 +-
 t/lfsr-test.c |  127 +++++++++++++++++
 6 files changed, 334 insertions(+), 239 deletions(-)
 create mode 100644 t/lfsr-test.c

---

Diff of recent changes:

diff --git a/Makefile b/Makefile
index d55626d..023557c 100644
--- a/Makefile
+++ b/Makefile
@@ -141,15 +141,21 @@ T_AXMAP_OBJS = t/axmap.o
 T_AXMAP_OBJS += lib/lfsr.o lib/axmap.o
 T_AXMAP_PROGS = t/axmap
 
+T_LFSR_TEST_OBJS = t/lfsr-test.o
+T_LFSR_TEST_OBJS += lib/lfsr.o
+T_LFSR_TEST_PROGS = t/lfsr-test
+
 T_OBJS = $(T_SMALLOC_OBJS)
 T_OBJS += $(T_IEEE_OBJS)
 T_OBJS += $(T_ZIPF_OBJS)
 T_OBJS += $(T_AXMAP_OBJS)
+T_OBJS += $(T_LFSR_TEST_OBJS)
 
 T_PROGS = $(T_SMALLOC_PROGS)
 T_PROGS += $(T_IEEE_PROGS)
 T_PROGS += $(T_ZIPF_PROGS)
 T_PROGS += $(T_AXMAP_PROGS)
+T_PROGS += $(T_LFSR_TEST_PROGS)
 
 ifneq ($(findstring $(MAKEFLAGS),s),s)
 ifndef V
@@ -204,6 +210,9 @@ t/genzipf: $(T_ZIPF_OBJS)
 t/axmap: $(T_AXMAP_OBJS)
 	$(QUIET_LINK)$(CC) $(LDFLAGS) $(CFLAGS) -o $@ $(T_AXMAP_OBJS) $(LIBS) $(LDFLAGS)
 
+t/lfsr-test: $(T_LFSR_TEST_OBJS)
+	$(QUIET_LINK)$(CC) $(LDFLAGS) $(CFLAGS) -o $@ $(T_LFSR_TEST_OBJS) $(LIBS) $(LDFLAGS)
+
 fio: $(OBJS)
 	$(QUIET_LINK)$(CC) $(LDFLAGS) $(CFLAGS) -o $@ $(OBJS) $(LIBS) $(LDFLAGS)
 
diff --git a/filesetup.c b/filesetup.c
index 220ceb9..57553c9 100644
--- a/filesetup.c
+++ b/filesetup.c
@@ -966,7 +966,7 @@ int init_random_map(struct thread_data *td)
 
 			seed = td->rand_seeds[FIO_RAND_BLOCK_OFF];
 			
-			if (!lfsr_init(&f->lfsr, blocks, seed))
+			if (!lfsr_init(&f->lfsr, blocks, seed, seed & 0xF))
 				continue;
 		} else if (!td->o.norandommap) {
 			f->io_axmap = axmap_new(blocks);
diff --git a/lib/lfsr.c b/lib/lfsr.c
index 61a3aaf..a835404 100644
--- a/lib/lfsr.c
+++ b/lib/lfsr.c
@@ -1,278 +1,233 @@
 #include <stdio.h>
+#include <math.h>
 
 #include "lfsr.h"
 
 /*
- * From table 3 of
+ * LFSR taps retrieved from:
+ * http://home1.gte.net/res0658s/electronics/LFSRtaps.html
  *
- * http://www.xilinx.com/support/documentation/application_notes/xapp052.pdf
+ * The memory overhead of the following tap table should be relatively small,
+ * no more than 400 bytes.
  */
-static struct lfsr_taps lfsr_taps[] = {
-	{
-		.length	= 16,
-		.taps	= { 16, 15, 13, 4, },
-	},
-	{
-		.length = 17,
-		.taps	= { 17, 14, },
-	},
-	{
-		.length = 18,
-		.taps	= { 18, 11, },
-	},
-	{
-		.length	= 19,
-		.taps	= { 19, 6, 2, 1, },
-	},
-	{
-		.length	= 20,
-		.taps	= { 20, 17, },
-	},
-	{
-		.length	= 21,
-		.taps	= { 21, 19, },
-	},
-	{
-		.length	= 22,
-		.taps	= { 22, 21, },
-	},
-	{
-		.length	= 23,
-		.taps	= { 23, 18, },
-	},
-	{
-		.length = 24,
-		.taps	= { 24, 23, 22, 17, },
-	},
-	{
-		.length	= 25,
-		.taps	= { 25, 22, },
-	},
-	{
-		.length	= 26,
-		.taps	= {26, 6, 2, 1, },
-	},
-	{
-		.length	= 27,
-		.taps	= { 27, 5, 2, 1, },
-	},
-	{
-		.length	= 28,
-		.taps	= { 28, 25, },
-	},
-	{
-		.length	= 29,
-		.taps	= {29, 27, },
-	},
-	{
-		.length	= 30,
-		.taps	= { 30, 6, 4, 1, },
-	},
-	{
-		.length	= 31,
-		.taps	= { 31, 28, },
-	},
-	{
-		.length	= 32,
-		.taps	= { 32, 22, 2, 1, },
-	},
-	{
-		.length	= 33,
-		.taps	= { 33, 20, },
-	},
-	{
-		.length	= 34,
-		.taps	= { 34, 27, 2, 1, },
-	},
-	{
-		.length	= 35,
-		.taps	= { 35, 33, },
-	},
-	{
-		.length	= 36,
-		.taps	= { 36, 25, },
-	},
-	{
-		.length	= 37,
-		.taps	= { 37, 5, 4, 3, 2, 1, },
-	},
-	{
-		.length	= 38,
-		.taps	= { 38, 6, 5, 1, },
-	},
-	{
-		.length	= 39,
-		.taps	= { 39, 35, },
-	},
-	{
-		.length	= 40,
-		.taps	= { 40, 38, 21, 19, },
-	},
-	{
-		.length	= 41,
-		.taps	= { 41, 38, },
-	},
-	{
-		.length	= 42,
-		.taps	= { 42, 41, 20, 19, },
-	},
-	{
-		.length	= 43,
-		.taps	= { 43, 42, 38, 37, },
-	},
-	{
-		.length	= 44,
-		.taps	= { 44, 43, 38, 37, },
-	},
-	{
-		.length	= 45,
-		.taps	= { 45, 44, 42, 41, },
-	},
-	{
-		.length	= 46,
-		.taps	= { 46, 45, 26, 25, },
-	},
-	{
-		.length	= 47,
-		.taps	= { 47, 42, },
-	},
-	{
-		.length	= 48,
-		.taps	= { 48, 47, 21, 20, },
-	},
-	{
-		.length	= 49,
-		.taps	= { 49, 40, },
-	},
-	{
-		.length	= 50,
-		.taps	= { 50, 49, 36, 35, },
-	},
-	{
-		.length	= 51,
-		.taps	= { 51, 50, 36, 35, },
-	},
-	{
-		.length	= 52,
-		.taps	= { 52, 49, },
-	},
-	{
-		.length	= 53,
-		.taps	= { 53, 52, 38, 37 },
-	},
-	{
-		.length	= 54,
-		.taps	= { 54, 53, 18, 17 },
-	},
-	{
-		.length	= 55,
-		.taps	= { 55, 31, },
-	},
-	{
-		.length	= 56,
-		.taps	= { 56, 55, 35, 34, },
-	},
-	{
-		.length	= 57,
-		.taps	= { 57, 50, },
-	},
-	{
-		.length = 58,
-		.taps	= { 58, 39, },
-	},
-	{
-		.length	= 59,
-		.taps	= { 59, 58, 38, 37, },
-	},
-	{
-		.length	= 60,
-		.taps	= { 60, 59, },
-	},
-	{
-		.length	= 61,
-		.taps	= { 61, 60, 46, 45, },
-	},
-	{
-		.length	= 62,
-		.taps	= { 62, 61, 6, 5, },
-	},
-	{
-		.length	= 63,
-		.taps	= { 63, 62, },
-	},
+static uint8_t taps[64][FIO_MAX_TAPS] =
+{
+	{0}, {0}, {0},		//LFSRs with less that 3-bits cannot exist
+	{3, 2},			//Tap position for 3-bit LFSR
+	{4, 3},			//Tap position for 4-bit LFSR
+	{5, 3},			//Tap position for 5-bit LFSR
+	{6, 5},			//Tap position for 6-bit LFSR
+	{7, 6},			//Tap position for 7-bit LFSR
+	{8, 6, 5 ,4},		//Tap position for 8-bit LFSR
+	{9, 5},			//Tap position for 9-bit LFSR
+	{10, 7},		//Tap position for 10-bit LFSR
+	{11, 9},		//Tap position for 11-bit LFSR
+	{12, 6, 4, 1},		//Tap position for 12-bit LFSR
+	{13, 4, 3, 1},		//Tap position for 13-bit LFSR
+	{14, 5, 3, 1},		//Tap position for 14-bit LFSR
+	{15, 14},		//Tap position for 15-bit LFSR
+	{16, 15, 13, 4},	//Tap position for 16-bit LFSR
+	{17, 14},		//Tap position for 17-bit LFSR
+	{18, 11},		//Tap position for 18-bit LFSR
+	{19, 6, 2, 1},		//Tap position for 19-bit LFSR
+	{20, 17},		//Tap position for 20-bit LFSR
+	{21, 19},		//Tap position for 21-bit LFSR
+	{22, 21},		//Tap position for 22-bit LFSR
+	{23, 18},		//Tap position for 23-bit LFSR
+	{24, 23, 22, 17},	//Tap position for 24-bit LFSR
+	{25, 22},		//Tap position for 25-bit LFSR
+	{26, 6, 2, 1},		//Tap position for 26-bit LFSR
+	{27, 5, 2, 1},		//Tap position for 27-bit LFSR
+	{28, 25},		//Tap position for 28-bit LFSR
+	{29, 27},		//Tap position for 29-bit LFSR
+	{30, 6, 4, 1},		//Tap position for 30-bit LFSR
+	{31, 28},		//Tap position for 31-bit LFSR
+	{32, 31, 29, 1},	//Tap position for 32-bit LFSR
+	{33, 20},		//Tap position for 33-bit LFSR
+	{34, 27, 2, 1},		//Tap position for 34-bit LFSR
+	{35, 33},		//Tap position for 35-bit LFSR
+	{36, 25},		//Tap position for 36-bit LFSR
+	{37, 5, 4, 3, 2, 1},	//Tap position for 37-bit LFSR
+	{38, 6, 5, 1},		//Tap position for 38-bit LFSR
+	{39, 35},		//Tap position for 39-bit LFSR
+	{40, 38, 21, 19},	//Tap position for 40-bit LFSR
+	{41, 38},		//Tap position for 41-bit LFSR
+	{42, 41, 20, 19},	//Tap position for 42-bit LFSR
+	{43, 42, 38, 37},	//Tap position for 43-bit LFSR
+	{44, 43, 18, 17},	//Tap position for 44-bit LFSR
+	{45, 44, 42, 41},	//Tap position for 45-bit LFSR
+	{46, 45, 26, 25},	//Tap position for 46-bit LFSR
+	{47, 42},		//Tap position for 47-bit LFSR
+	{48, 47, 21, 20},	//Tap position for 48-bit LFSR
+	{49, 40},		//Tap position for 49-bit LFSR
+	{50, 49, 24, 23},	//Tap position for 50-bit LFSR
+	{51, 50, 36, 35},	//Tap position for 51-bit LFSR
+	{52, 49},		//Tap position for 52-bit LFSR
+	{53, 52, 38, 37},	//Tap position for 53-bit LFSR
+	{54, 53, 18, 17},	//Tap position for 54-bit LFSR
+	{55, 31},		//Tap position for 55-bit LFSR
+	{56, 55, 35, 34},	//Tap position for 56-bit LFSR
+	{57, 50},		//Tap position for 57-bit LFSR
+	{58, 39},		//Tap position for 58-bit LFSR
+	{59, 58, 38, 37},	//Tap position for 59-bit LFSR
+	{60, 59},		//Tap position for 60-bit LFSR
+	{61, 60, 46, 45},	//Tap position for 61-bit LFSR
+	{62, 61, 6, 5},		//Tap position for 62-bit LFSR
+	{63, 62},		//Tap position for 63-bit LFSR
 };
 
-#define FIO_LFSR_CRANKS		128
+#define __LFSR_NEXT(__fl, __v)						\
+	__v = ((__v >> 1) | __fl->cached_bit) ^			\
+			(((__v & 1UL) - 1UL) & __fl->xormask);
 
-static uint64_t __lfsr_next(uint64_t v, struct lfsr_taps *lt)
+static inline void __lfsr_next(struct fio_lfsr *fl, unsigned int spin)
 {
-	uint64_t xor_mask = 0;
-	int i;
-
-	for (i = 0; lt->taps[i]; i++)
-		xor_mask ^= (v << (lt->taps[i] - 1));
-
-	xor_mask &= ~(~0UL << 1) << (lt->length - 1);
-	return xor_mask | (v >> 1);
+	/*
+	 * This should be O(1) since most compilers will create a jump table for
+	 * 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);
+		case 12: __LFSR_NEXT(fl, fl->last_val);
+		case 11: __LFSR_NEXT(fl, fl->last_val);
+		case 10: __LFSR_NEXT(fl, fl->last_val);
+		case  9: __LFSR_NEXT(fl, fl->last_val);
+		case  8: __LFSR_NEXT(fl, fl->last_val);
+		case  7: __LFSR_NEXT(fl, fl->last_val);
+		case  6: __LFSR_NEXT(fl, fl->last_val);
+		case  5: __LFSR_NEXT(fl, fl->last_val);
+		case  4: __LFSR_NEXT(fl, fl->last_val);
+		case  3: __LFSR_NEXT(fl, fl->last_val);
+		case  2: __LFSR_NEXT(fl, fl->last_val);
+		case  1: __LFSR_NEXT(fl, fl->last_val);
+		case  0: __LFSR_NEXT(fl, fl->last_val);
+		default: break;
+	}
 }
 
 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;
+
 	if (fl->num_vals > fl->max_val)
 		return 1;
 
+	fl->num_vals++;
+
 	do {
-		fl->last_val = __lfsr_next(fl->last_val, &fl->taps);
-		if (fl->last_val - 1 <= fl->max_val &&
-		    fl->last_val <= last)
-			break;
-	} while (1);
+		__lfsr_next(fl, spin);
+	} while (fl->last_val > fl->max_val);
 
-	*off = fl->last_val - 1;
-	fl->num_vals++;
+	*off = fl->last_val;
 	return 0;
 }
 
-static struct lfsr_taps *find_lfsr(uint64_t size)
+static uint64_t lfsr_create_xormask(uint8_t *taps)
 {
 	int i;
+	uint64_t xormask = 0;
 
-	for (i = 0; lfsr_taps[i].length; i++)
-		if (((1UL << lfsr_taps[i].length) + FIO_LFSR_CRANKS) >= size)
-			return &lfsr_taps[i];
+	for(i = 0; i < FIO_MAX_TAPS && taps[i] != 0; i++)
+		xormask |= 1UL << (taps[i] - 1);
 
-	return NULL;
+	return xormask;
 }
 
-void lfsr_reset(struct fio_lfsr *fl, unsigned long seed)
+static uint8_t *find_lfsr(uint64_t size)
 {
-	unsigned int i;
+	int i;
 
-	fl->last_val = seed;
-	fl->num_vals = 0;
+	for (i = 3; i < 64; i++)
+		if ((1UL << i) > size) /* TODO: Explain why. */
+			return taps[i];
 
-	for (i = 0; i < FIO_LFSR_CRANKS; i++)
-		fl->last_val = __lfsr_next(fl->last_val, &fl->taps);
+	return NULL;
 }
 
-int lfsr_init(struct fio_lfsr *fl, uint64_t size, unsigned long seed)
+/*
+ * It is well-known that all maximal n-bit LFSRs will start repeating
+ * themselves after their 2^n iteration. The introduction of spins however, is
+ * possible to create a repetition of a sub-sequence before we hit that mark.
+ * This happens if:
+ *
+ * [1]: ((2^n - 1) * i) % (spin + 1) == 0,
+ * where "n" is LFSR's bits and "i" any number within the range [1,spin]
+ *
+ * It is important to know beforehand if a spin can cause a repetition of a
+ * sub-sequence (cycle) and its length. However, calculating (2^n - 1) * i may
+ * produce a buffer overflow for "n" close to 64, so we expand the above to:
+ *
+ * [2]: (2^n - 1) -> (x * (spin + 1) + y), where x >= 0 and 0 <= y <= spin
+ *
+ * Thus, [1] is equivalent to (y * i) % (spin + 1) == 0;
+ * Also, the cycle's length will be (x * i) + (y * i) / (spin + 1)
+ */
+int prepare_spin(struct fio_lfsr *fl, unsigned int spin)
 {
-	struct lfsr_taps *tap;
+	uint64_t max = (fl->cached_bit << 1) - 1;
+	uint64_t x, y;
 	int i;
 
-	tap = find_lfsr(size);
-	if (!tap)
+	if (spin > 15)
 		return 1;
 
-	fl->max_val = size - 1;
-	fl->taps.length = tap->length;
+	x = max / (spin + 1);
+	y = max % (spin + 1);
+	fl->cycle_length = max;	/* This is the expected cycle */
+	fl->spin = spin;
 
-	for (i = 0; i < FIO_MAX_TAPS; i++) {
-		fl->taps.taps[i] = tap->taps[i];
-		if (!fl->taps.taps[i])
+	for (i = 1; i <= spin; i++) {
+		if ((y * i) % (spin + 1) == 0) {
+			fl->cycle_length = (x * i) + (y * i) / (spin + 1);
 			break;
+		}
 	}
 
-	lfsr_reset(fl, seed);
+	return 0;
+}
+
+int lfsr_reset(struct fio_lfsr *fl, unsigned long seed)
+{
+	uint64_t bitmask = (fl->cached_bit << 1) - 1;
+
+	fl->num_vals = 0;
+	fl->last_val = seed & bitmask;
+
+	/* All-ones state is illegal for XNOR LFSRs */
+	if (fl->last_val == bitmask)
+		return 1;
+
+	return 0;
+}
+
+int lfsr_init(struct fio_lfsr *fl, uint64_t nums, unsigned long seed,
+		unsigned int spin)
+{
+	uint8_t *lfsr_taps;
+
+	lfsr_taps = find_lfsr(nums);
+	if (!lfsr_taps)
+		return 1;
+
+	fl->max_val = nums - 1;
+	fl->xormask = lfsr_create_xormask(lfsr_taps);
+	fl->cached_bit = 1UL << (lfsr_taps[0] - 1);
+
+	if (prepare_spin(fl, spin))
+		return 1;
+
+	if (lfsr_reset(fl, seed))
+		return 1;
+
 	return 0;
 }
diff --git a/lib/lfsr.h b/lib/lfsr.h
index 45d7028..bc16af9 100644
--- a/lib/lfsr.h
+++ b/lib/lfsr.h
@@ -3,7 +3,7 @@
 
 #include <inttypes.h>
 
-#define FIO_MAX_TAPS	8
+#define FIO_MAX_TAPS	6
 
 struct lfsr_taps {
 	unsigned int length;
@@ -12,14 +12,18 @@ struct lfsr_taps {
 
 
 struct fio_lfsr {
+	uint64_t xormask;
 	uint64_t last_val;
+	uint64_t cached_bit;
 	uint64_t max_val;
 	uint64_t num_vals;
-	struct lfsr_taps taps;
+	uint64_t cycle_length;
+	unsigned int spin;
 };
 
 int lfsr_next(struct fio_lfsr *fl, uint64_t *off, uint64_t);
-int lfsr_init(struct fio_lfsr *fl, uint64_t size, unsigned long seed);
-void lfsr_reset(struct fio_lfsr *fl, unsigned long seed);
+int lfsr_init(struct fio_lfsr *fl, uint64_t size,
+		unsigned long seed, unsigned int spin);
+int lfsr_reset(struct fio_lfsr *fl, unsigned long seed);
 
 #endif
diff --git a/t/axmap.c b/t/axmap.c
index 61e3220..7ab500f 100644
--- a/t/axmap.c
+++ b/t/axmap.c
@@ -34,7 +34,7 @@ int main(int argc, char *argv[])
 
 	printf("Using %llu entries\n", (unsigned long long) size);
 
-	lfsr_init(&lfsr, size, seed);
+	lfsr_init(&lfsr, size, seed, seed & 0xF);
 	map = axmap_new(size);
 	osize = size;
 
diff --git a/t/lfsr-test.c b/t/lfsr-test.c
new file mode 100644
index 0000000..193a7f9
--- /dev/null
+++ b/t/lfsr-test.c
@@ -0,0 +1,127 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <time.h>
+#include <math.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+
+#include "../lib/lfsr.h"
+
+void usage()
+{
+	printf("Usage: lfsr-test 0x<numbers> [seed] [spin] [verify]\n");
+	printf("-------------------------------------------------------------\n");
+	printf("*numbers: how many random numbers to produce (in hex)\n"
+		   "seed:     initial value\n"
+		   "spin:     how many iterations before we produce a number\n"
+		   "verify:   check if LFSR has iterated correctly\n\n"
+		   "Only <numbers> is required. The rest are evaluated to 0 or false\n"
+		   "Elapsed/mean time and verification results are printed at the"
+	       "end of the test\n");
+}
+
+int main(int argc, char *argv[])
+{
+	int r;
+	struct timespec start, end;
+	struct fio_lfsr *fl;
+	int verify = 0;
+	unsigned int spin = 0;
+	uint64_t seed = 0;
+	uint64_t numbers;
+	uint64_t v_size;
+	uint64_t i;
+	void *v = NULL, *v_start;
+	double total, mean;
+
+	/* Read arguments */
+	switch (argc) {
+		case 5: if (strncmp(argv[4], "verify", 7) == 0)
+					verify = 1;
+		case 4: spin = atoi(argv[3]);
+		case 3: seed = atol(argv[2]);
+		case 2: numbers = strtol(argv[1], NULL, 16);
+				break;
+		default: usage();
+				 return 1;
+	}
+
+	/* Initialize LFSR */
+	fl = malloc(sizeof(struct fio_lfsr));
+	if (!fl) {
+		perror("malloc");
+		return 1;
+	}
+
+	r = lfsr_init(fl, numbers, seed, spin);
+	if (r) {
+		printf("Initialization failed.\n");
+		return r;
+	}
+
+	/* Print specs */
+	printf("LFSR specs\n");
+	printf("==========================\n");
+	printf("Size is         %u\n", 64 - __builtin_clzl(fl->cached_bit));
+	printf("Max val is      %lu\n", fl->max_val);
+	printf("XOR-mask is     0x%lX\n", fl->xormask);
+	printf("Seed is         %lu\n", fl->last_val);
+	printf("Spin is         %u\n", fl->spin);
+	printf("Cycle length is %lu\n", fl->cycle_length);
+
+	/* Create verification table */
+	if (verify) {
+		v_size = numbers * sizeof(uint8_t);
+		v = malloc(v_size);
+		memset(v, 0, v_size);
+		printf("\nVerification table is %lf KBs\n", (double)(v_size) / 1024);
+	}
+	v_start = v;
+
+	/*
+	 * Iterate over a tight loop until we have produced all the requested
+	 * numbers. Verifying the results should introduce some small yet not
+	 * negligible overhead.
+	 */
+	fprintf(stderr, "\nTest initiated... ");
+	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);
+	while (!lfsr_next(fl, &i, fl->max_val)) {
+		if (verify)
+			*(uint8_t *)(v + i) += 1;
+	}
+	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");
+				r = 1;
+				break;
+			}
+		}
+		if (!r)
+			fprintf(stderr, "OK!\n");
+	}
+
+	/* Calculate elapsed time and mean time per number */
+	total = (end.tv_sec - start.tv_sec) * pow(10,9) +
+		end.tv_nsec - start.tv_nsec;
+	mean = total / fl->num_vals;
+
+	printf("\nTime results ");
+	if (verify)
+		printf("(slower due to verification)");
+	printf("\n==============================\n");
+	printf("Elapsed: %lf s\n", total / pow(10,9));
+	printf("Mean:    %lf ns\n", mean);
+
+	free(v_start);
+	free(fl);
+	return r;
+}
--
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