[RFC PATCH 5/7] rslib: Fix handling of of caller provided syndrome

[Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com>]

Check if the syndrome provided by the caller is zero, and act
accordingly.

Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com>
---
 lib/reed_solomon/decode_rs.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
index 78629bbe6590..7ecc449e57e9 100644
--- a/lib/reed_solomon/decode_rs.c
+++ b/lib/reed_solomon/decode_rs.c
@@ -42,8 +42,16 @@
 	BUG_ON(pad < 0 || pad >= nn - nroots);
 
 	/* Does the caller provide the syndrome ? */
-	if (s != NULL)
-		goto decode;
+	if (s != NULL) {
+	    for (i = 0; i < nroots; i++) {
+		    /* The syndrome is in index form, so nn represents zero */
+		    if (s[i] != nn)
+			    goto decode;
+	    }
+
+	    /* syndrome is zero, no errors to correct  */
+	    return 0;
+	}
 
 	/* form the syndromes; i.e., evaluate data(x) at roots of
 	 * g(x) */
-- 
2.17.2