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rslib: Fix decoding of shortened codes

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[ Upstream commit 2034a42d1747fc1e1eeef2c6f1789c4d0762cb9c ]

The decoding of shortenend codes is broken. It only works as expected if
there are no erasures.

When decoding with erasures, Lambda (the error and erasure locator
polynomial) is initialized from the given erasure positions. The pad
parameter is not accounted for by the initialisation code, and hence
Lambda is initialized from incorrect erasure positions.

The fix is to adjust the erasure positions by the supplied pad.

Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190620141039.9874-3-ferdinand.blomqvist@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Ferdinand Blomqvist 2019-06-20 17:10:34 +03:00 committed by Greg Kroah-Hartman
parent 3d2af3adea
commit a7a7839b55
1 changed files with 2 additions and 2 deletions
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4
lib/reed_solomon/decode_rs.c
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@ -99,9 +99,9 @@
if (no_eras > 0) {
/* Init lambda to be the erasure locator polynomial */
lambda[1] = alpha_to[rs_modnn(rs,
prim * (nn - 1 - eras_pos[0]))];
prim * (nn - 1 - (eras_pos[0] + pad)))];
for (i = 1; i < no_eras; i++) {
u = rs_modnn(rs, prim * (nn - 1 - eras_pos[i]));
u = rs_modnn(rs, prim * (nn - 1 - (eras_pos[i] + pad)));
for (j = i + 1; j > 0; j--) {
tmp = index_of[lambda[j - 1]];
if (tmp != nn) {