Hi!
On 2020-06-25 00:36:01, Aiden Leong wrote:
Corr and eras_pos are updated to actual correction pattern and erasure
positions, but no_eras is not.
When this library is used to recover lost bytes, we normally memset the
lost trunk of bytes to zero as a placeholder. Unfortunately, if the lost
byte is zero, b[i] is zero too. Without correct no_eras, users won't be
able to determine the valid length of corr and eras_pos.
Signed-off-by: Aiden Leong <aiden.leong@xxxxxxxxx>
I'm not sure I understand what you try to do. decode_rs* already returns
the number of errors correted (or something negative upon failure). So
your last statment is false. The lengt of corr and eras_pos is returned
by the function. So this change is unnecessary. More comments inline.
diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
index 805de84ae83d..44136ea33d16 100644
--- a/lib/reed_solomon/decode_rs.c
+++ b/lib/reed_solomon/decode_rs.c
@@ -24,6 +24,7 @@
int count = 0;
int num_corrected;
uint16_t msk = (uint16_t) rs->nn;
+ int no_eras_local = no_eras ? *no_eras : 0;
/*
* The decoder buffers are in the rs control struct. They are
@@ -106,11 +107,11 @@
memset(&lambda[1], 0, nroots * sizeof(lambda[0]));
lambda[0] = 1;
- if (no_eras > 0) {
+ if (no_eras_local > 0) {
/* Init lambda to be the erasure locator polynomial */
lambda[1] = alpha_to[rs_modnn(rs,
prim * (nn - 1 - (eras_pos[0] + pad)))];
- for (i = 1; i < no_eras; i++) {
+ for (i = 1; i < no_eras_local; 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]];
@@ -129,8 +130,8 @@
* Begin Berlekamp-Massey algorithm to determine error+erasure
* locator polynomial
*/
- r = no_eras;
- el = no_eras;
+ r = no_eras_local;
+ el = no_eras_local;
while (++r <= nroots) { /* r is the step number */
/* Compute discrepancy at the r-th step in poly-form */
discr_r = 0;
@@ -158,8 +159,8 @@
} else
t[i + 1] = lambda[i + 1];
}
- if (2 * el <= r + no_eras - 1) {
- el = r + no_eras - el;
+ if (2 * el <= r + no_eras_local - 1) {
+ el = r + no_eras_local - el;
/*
* 2 lines below: B(x) <-- inv(discr_r) *
* lambda(x)
@@ -312,14 +313,21 @@
eras_pos[j++] = loc[i] - pad;
}
}
+ if (no_eras)
+ *no_eras = j;
At this point j will be equal to num_corrected. So why return this
information in no_eras, when it is already returned by the function?
} else if (data && par) {
/* Apply error to data and parity */
+ j = 0;
for (i = 0; i < count; i++) {
if (loc[i] < (nn - nroots))
data[loc[i] - pad] ^= b[i];
else
par[loc[i] - pad - len] ^= b[i];
+ if (b[i])
+ j++;
}
+ if (no_eras)
+ *no_eras = j;
Same as above.
2.25.1
Best,
Ferdinand
--
Ferdinand Blomqvist
ferdinand.blomqvist[at]gmail.com
GPG key: 9EFB 7A2C 0432 4EC5 32BA FA61 CFE9 4164 93E8 B9E4
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