X-Git-Url: https://git.kernel.dk/?a=blobdiff_plain;f=lib%2Flfsr.c;h=61a3aaf3e6532c32722314da125bcce69cf98416;hb=44cbc6daaae3674ea5d0a113b66596ca24f372e0;hp=64442ab536d40fc2ac3894fc30043fcc94ef1e2b;hpb=8055e41d0ecc54770a2653427532b3e2c5fabdad;p=fio.git

diff --git a/lib/lfsr.c b/lib/lfsr.c
index 64442ab5..61a3aaf3 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;
@@ -214,14 +216,15 @@ static uint64_t __lfsr_next(uint64_t v, struct lfsr_taps *lt)
 	return xor_mask | (v >> 1);
 }
 
-int lfsr_next(struct fio_lfsr *fl, uint64_t *off)
+int lfsr_next(struct fio_lfsr *fl, uint64_t *off, uint64_t last)
 {
 	if (fl->num_vals > fl->max_val)
 		return 1;
 
 	do {
 		fl->last_val = __lfsr_next(fl->last_val, &fl->taps);
-		if (fl->last_val - 1 <= fl->max_val)
+		if (fl->last_val - 1 <= fl->max_val &&
+		    fl->last_val <= last)
 			break;
 	} while (1);
 
@@ -235,13 +238,24 @@ 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;
 }
 
-int lfsr_init(struct fio_lfsr *fl, uint64_t size)
+void lfsr_reset(struct fio_lfsr *fl, unsigned long seed)
+{
+	unsigned int i;
+
+	fl->last_val = seed;
+	fl->num_vals = 0;
+
+	for (i = 0; i < FIO_LFSR_CRANKS; i++)
+		fl->last_val = __lfsr_next(fl->last_val, &fl->taps);
+}
+
+int lfsr_init(struct fio_lfsr *fl, uint64_t size, unsigned long seed)
 {
 	struct lfsr_taps *tap;
 	int i;
@@ -250,15 +264,15 @@ int lfsr_init(struct fio_lfsr *fl, uint64_t size)
 	if (!tap)
 		return 1;
 
-	fl->last_val = 1;
 	fl->max_val = size - 1;
-	fl->num_vals = 0;
 	fl->taps.length = tap->length;
+
 	for (i = 0; i < FIO_MAX_TAPS; i++) {
 		fl->taps.taps[i] = tap->taps[i];
 		if (!fl->taps.taps[i])
 			break;
 	}
 
+	lfsr_reset(fl, seed);
 	return 0;
 }