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[RSLIB] Support non-canonical GF representations
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For the CAFÉ NAND controller, we need to support non-canonical 
representations of the Galois field. Allow the caller to provide its own 
function for generating the field, and CAFÉ can use rslib instead of its
own implementation.

Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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@segher @dwmw2
segher authored and dwmw2 committed May 2, 2007
1 parent 7c96b7a commit d7e5a54
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Showing 2 changed files with 73 additions and 15 deletions.
4 changes: 4 additions & 0 deletions include/linux/rslib.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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
*/
Expand All @@ -48,6 +49,7 @@ struct rs_control {
int prim;
int iprim;
int gfpoly;
int (*gffunc)(int);
int users;
struct list_head list;
};
Expand Down Expand Up @@ -77,6 +79,8 @@ int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
/* 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);
Expand Down
84 changes: 69 additions & 15 deletions lib/reed_solomon/reed_solomon.c
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Original file line number Diff line number Diff line change
Expand Up @@ -56,15 +56,16 @@ static DEFINE_MUTEX(rslistlock);
* 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)
*
* 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;
Expand All @@ -82,6 +83,7 @@ static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
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);
Expand All @@ -99,17 +101,26 @@ static struct rs_control *rs_init(int symsize, int gfpoly, int fcr,
/* 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 */
Expand Down Expand Up @@ -173,18 +184,22 @@ void free_rs(struct rs_control *rs)
}

/**
* 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;
Expand All @@ -208,6 +223,8 @@ struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
continue;
if (gfpoly != rs->gfpoly)
continue;
if (gffunc != rs->gffunc)
continue;
if (fcr != rs->fcr)
continue;
if (prim != rs->prim)
Expand All @@ -220,7 +237,7 @@ struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
}

/* 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);
Expand All @@ -230,6 +247,42 @@ struct rs_control *init_rs(int symsize, int gfpoly, int fcr, int prim,
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)
Expand Down Expand Up @@ -321,6 +374,7 @@ EXPORT_SYMBOL_GPL(decode_rs16);
#endif

EXPORT_SYMBOL_GPL(init_rs);
EXPORT_SYMBOL_GPL(init_rs_non_canonical);
EXPORT_SYMBOL_GPL(free_rs);

MODULE_LICENSE("GPL");
Expand Down

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