// SPDX-License-Identifier: GPL-2.0
/*
 * Generic Reed Solomon encoder / decoder library
 *
 * Copyright (C) 2004 Thomas Gleixner (tglx@kernel.org)
 *
 * RS code lifted from reed solomon library written by Phil Karn
 * Copyright 2002 Phil Karn, KA9Q
 */
#ifndef _RSLIB_H_
#define _RSLIB_H_

#include <linux/types.h>        /* for gfp_t */
#include <linux/gfp.h>          /* for GFP_KERNEL */

/**
 * struct rs_codec - rs codec data
 *
 * @mm:         Bits per symbol
 * @nn:         Symbols per block (= (1<<mm)-1)
 * @alpha_to:   log lookup table
 * @index_of:   Antilog lookup table
 * @genpoly:    Generator polynomial
 * @nroots:     Number of generator roots = number of parity symbols
 * @fcr:        First consecutive root, index form
 * @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 codec list
*/
struct rs_codec {
        int             mm;
        int             nn;
        uint16_t        *alpha_to;
        uint16_t        *index_of;
        uint16_t        *genpoly;
        int             nroots;
        int             fcr;
        int             prim;
        int             iprim;
        int             gfpoly;
        int             (*gffunc)(int);
        int             users;
        struct list_head list;
};

/**
 * struct rs_control - rs control structure per instance
 * @codec:      The codec used for this instance
 * @buffers:    Internal scratch buffers used in calls to decode_rs()
 */
struct rs_control {
        struct rs_codec *codec;
        uint16_t        buffers[];
};

/* General purpose RS codec, 8-bit data width, symbol width 1-15 bit  */
#ifdef CONFIG_REED_SOLOMON_ENC8
int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
               uint16_t invmsk);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC8
int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
                uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
               uint16_t *corr);
#endif

/* General purpose RS codec, 16-bit data width, symbol width 1-15 bit  */
#ifdef CONFIG_REED_SOLOMON_ENC16
int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
                uint16_t invmsk);
#endif
#ifdef CONFIG_REED_SOLOMON_DEC16
int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
                uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
                uint16_t *corr);
#endif

struct rs_control *init_rs_gfp(int symsize, int gfpoly, int fcr, int prim,
                               int nroots, gfp_t gfp);

/**
 * init_rs - Create a RS control struct and initialize it
 *  @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)
 *
 * Allocations use GFP_KERNEL.
 */
static inline struct rs_control *init_rs(int symsize, int gfpoly, int fcr,
                                         int prim, int nroots)
{
        return init_rs_gfp(symsize, gfpoly, fcr, prim, nroots, GFP_KERNEL);
}

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);

/** modulo replacement for galois field arithmetics
 *
 *  @rs:        Pointer to the RS codec
 *  @x:         the value to reduce
 *
 *  where
 *  rs->mm = number of bits per symbol
 *  rs->nn = (2^rs->mm) - 1
 *
 *  Simple arithmetic modulo would return a wrong result for values
 *  >= 3 * rs->nn
*/
static inline int rs_modnn(struct rs_codec *rs, int x)
{
        while (x >= rs->nn) {
                x -= rs->nn;
                x = (x >> rs->mm) + (x & rs->nn);
        }
        return x;
}

#endif