From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 27 Nov 2012 07:21:18 +0000 (+0100)
Subject: lfsr: crank it 128 times before using the sequence
X-Git-Tag: fio-2.0.12~38^2~4
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=c4fc0ff1a313de8f113689950d36eabea65ce310

lfsr: crank it 128 times before using the sequence

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/lib/lfsr.c b/lib/lfsr.c
index 64442ab5..01c97cb8 100644
--- a/lib/lfsr.c
+++ b/lib/lfsr.c
@@ -3,7 +3,7 @@
 #include "lfsr.h"
 
 /*
- * Trom table 3 of
+ * From table 3 of
  *
  * http://www.xilinx.com/support/documentation/application_notes/xapp052.pdf
  */
@@ -202,6 +202,8 @@ static struct lfsr_taps lfsr_taps[] = {
 	},
 };
 
+#define FIO_LFSR_CRANKS		128
+
 static uint64_t __lfsr_next(uint64_t v, struct lfsr_taps *lt)
 {
 	uint64_t xor_mask = 0;
@@ -235,7 +237,7 @@ static struct lfsr_taps *find_lfsr(uint64_t size)
 	int i;
 
 	for (i = 0; lfsr_taps[i].length; i++)
-		if ((1UL << lfsr_taps[i].length) >= size)
+		if (((1UL << lfsr_taps[i].length) + FIO_LFSR_CRANKS) >= size)
 			return &lfsr_taps[i];
 
 	return NULL;
@@ -260,5 +262,8 @@ int lfsr_init(struct fio_lfsr *fl, uint64_t size)
 			break;
 	}
 
+	for (i = 0; i < FIO_LFSR_CRANKS; i++)
+		fl->last_val = __lfsr_next(fl->last_val, &fl->taps);
+
 	return 0;
 }