[PATCH rslib] Support non-canonical GF representations
Segher Boessenkool
segher at kernel.crashing.org
Wed May 2 06:18:41 EDT 2007
Signed-off-by: Segher Boessenkool <segher at kernel.crashing.org>
---
include/linux/rslib.h | 4 +
lib/reed_solomon/reed_solomon.c | 84 ++++++++++++++++++++++++++------
2 files changed, 73 insertions(+), 15 deletions(-)
Index: linux-2.6/include/linux/rslib.h
===================================================================
--- linux-2.6.orig/include/linux/rslib.h
+++ linux-2.6/include/linux/rslib.h
@@ -34,6 +34,7 @@
* @prim: Primitive element, index form
* @iprim: prim-th root of 1, index form
* @gfpoly: The primitive generator polynominal
+ * @gffunc: Function to generate the field, if non-canonical representation
* @users: Users of this structure
* @list: List entry for the rs control list
*/
@@ -48,6 +49,7 @@
int prim;
int iprim;
int gfpoly;
+ int (*gffunc)(int);
int users;
struct list_head list;
};
@@ -77,6 +79,8 @@
/* Create or get a matching rs control structure */
struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
int nroots);
+struct rs_control *init_rs_non_canonical(int symsize, int (*func)(int),
+ int fcr, int prim, int nroots);
/* Release a rs control structure */
void free_rs(struct rs_control *rs);
Index: linux-2.6/lib/reed_solomon/reed_solomon.c
===================================================================
--- linux-2.6.orig/lib/reed_solomon/reed_solomon.c
+++ linux-2.6/lib/reed_solomon/reed_solomon.c
@@ -56,6 +56,7 @@
* rs_init - Initialize a Reed-Solomon codec
* @symsize: symbol size, bits (1-8)
* @gfpoly: Field generator polynomial coefficients
+ * @gffunc: Field generator function
* @fcr: first root of RS code generator polynomial, index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
@@ -63,8 +64,8 @@
* Allocate a control structure and the polynom arrays for faster
* en/decoding. Fill the arrays according to the given parameters.
*/
-static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
- int prim, int nroots)
+static struct rs_control *rs_init(int symsize, int gfpoly, int (*gffunc)(int),
+ int fcr, int prim, int nroots)
{
struct rs_control *rs;
int i, j, sr, root, iprim;
@@ -82,6 +83,7 @@
rs->prim = prim;
rs->nroots = nroots;
rs->gfpoly = gfpoly;
+ rs->gffunc = gffunc;
/* Allocate the arrays */
rs->alpha_to = kmalloc(sizeof(uint16_t) * (rs->nn + 1), GFP_KERNEL);
@@ -99,17 +101,26 @@
/* Generate Galois field lookup tables */
rs->index_of[0] = rs->nn; /* log(zero) = -inf */
rs->alpha_to[rs->nn] = 0; /* alpha**-inf = 0 */
- sr = 1;
- for (i = 0; i < rs->nn; i++) {
- rs->index_of[sr] = i;
- rs->alpha_to[i] = sr;
- sr <<= 1;
- if (sr & (1 << symsize))
- sr ^= gfpoly;
- sr &= rs->nn;
+ if (gfpoly) {
+ sr = 1;
+ for (i = 0; i < rs->nn; i++) {
+ rs->index_of[sr] = i;
+ rs->alpha_to[i] = sr;
+ sr <<= 1;
+ if (sr & (1 << symsize))
+ sr ^= gfpoly;
+ sr &= rs->nn;
+ }
+ } else {
+ sr = gffunc(0);
+ for (i = 0; i < rs->nn; i++) {
+ rs->index_of[sr] = i;
+ rs->alpha_to[i] = sr;
+ sr = gffunc(sr);
+ }
}
/* If it's not primitive, exit */
- if(sr != 1)
+ if(sr != rs->alpha_to[0])
goto errpol;
/* Find prim-th root of 1, used in decoding */
@@ -173,18 +184,22 @@
}
/**
- * init_rs - Find a matching or allocate a new rs control structure
+ * init_rs_internal - Find a matching or allocate a new rs control structure
* @symsize: the symbol size (number of bits)
* @gfpoly: the extended Galois field generator polynomial coefficients,
* with the 0th coefficient in the low order bit. The polynomial
* must be primitive;
+ * @gffunc: pointer to function to generate the next field element,
+ * or the multiplicative identity element if given 0. Used
+ * instead of gfpoly if gfpoly is 0
* @fcr: the first consecutive root of the rs code generator polynomial
* in index form
* @prim: primitive element to generate polynomial roots
* @nroots: RS code generator polynomial degree (number of roots)
*/
-struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
- int nroots)
+static struct rs_control *init_rs_internal(int symsize, int gfpoly,
+ int (*gffunc)(int), int fcr,
+ int prim, int nroots)
{
struct list_head *tmp;
struct rs_control *rs;
@@ -208,6 +223,8 @@
continue;
if (gfpoly != rs->gfpoly)
continue;
+ if (gffunc != rs->gffunc)
+ continue;
if (fcr != rs->fcr)
continue;
if (prim != rs->prim)
@@ -220,7 +237,7 @@
}
/* Create a new one */
- rs = rs_init(symsize, gfpoly, fcr, prim, nroots);
+ rs = rs_init(symsize, gfpoly, gffunc, fcr, prim, nroots);
if (rs) {
rs->users = 1;
list_add(&rs->list, &rslist);
@@ -230,6 +247,42 @@
return rs;
}
+/**
+ * init_rs - Find a matching or allocate a new rs control structure
+ * @symsize: the symbol size (number of bits)
+ * @gfpoly: the extended Galois field generator polynomial coefficients,
+ * with the 0th coefficient in the low order bit. The polynomial
+ * must be primitive;
+ * @fcr: the first consecutive root of the rs code generator polynomial
+ * in index form
+ * @prim: primitive element to generate polynomial roots
+ * @nroots: RS code generator polynomial degree (number of roots)
+ */
+struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
+ int nroots)
+{
+ return init_rs_internal(symsize, gfpoly, NULL, fcr, prim, nroots);
+}
+
+/**
+ * init_rs_non_canonical - Find a matching or allocate a new rs control
+ * structure, for fields with non-canonical
+ * representation
+ * @symsize: the symbol size (number of bits)
+ * @gffunc: pointer to function to generate the next field element,
+ * or the multiplicative identity element if given 0. Used
+ * instead of gfpoly if gfpoly is 0
+ * @fcr: the first consecutive root of the rs code generator polynomial
+ * in index form
+ * @prim: primitive element to generate polynomial roots
+ * @nroots: RS code generator polynomial degree (number of roots)
+ */
+struct rs_control *init_rs_non_canonical(int symsize, int (*gffunc)(int),
+ int fcr, int prim, int nroots)
+{
+ return init_rs_internal(symsize, 0, gffunc, fcr, prim, nroots);
+}
+
#ifdef CONFIG_REED_SOLOMON_ENC8
/**
* encode_rs8 - Calculate the parity for data values (8bit data width)
@@ -321,6 +374,7 @@
#endif
EXPORT_SYMBOL_GPL(init_rs);
+EXPORT_SYMBOL_GPL(init_rs_non_canonical);
EXPORT_SYMBOL_GPL(free_rs);
MODULE_LICENSE("GPL");
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