rslib.h

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Generic Reed Solomon encoder / decoder library
  4 *
  5 * Copyright (C) 2004 Thomas Gleixner (tglx@kernel.org)
  6 *
  7 * RS code lifted from reed solomon library written by Phil Karn
  8 * Copyright 2002 Phil Karn, KA9Q
  9 */
 10#ifndef _RSLIB_H_
 11#define _RSLIB_H_
 12
 13#include <linux/types.h>	/* for gfp_t */
 14#include <linux/gfp.h>		/* for GFP_KERNEL */
 15
 16/**
 17 * struct rs_codec - rs codec data
 18 *
 19 * @mm:		Bits per symbol
 20 * @nn:		Symbols per block (= (1<<mm)-1)
 21 * @alpha_to:	log lookup table
 22 * @index_of:	Antilog lookup table
 23 * @genpoly:	Generator polynomial
 24 * @nroots:	Number of generator roots = number of parity symbols
 25 * @fcr:	First consecutive root, index form
 26 * @prim:	Primitive element, index form
 27 * @iprim:	prim-th root of 1, index form
 28 * @gfpoly:	The primitive generator polynominal
 29 * @gffunc:	Function to generate the field, if non-canonical representation
 30 * @users:	Users of this structure
 31 * @list:	List entry for the rs codec list
 32*/
 33struct rs_codec {
 34	int		mm;
 35	int		nn;
 36	uint16_t	*alpha_to;
 37	uint16_t	*index_of;
 38	uint16_t	*genpoly;
 39	int		nroots;
 40	int		fcr;
 41	int		prim;
 42	int		iprim;
 43	int		gfpoly;
 44	int		(*gffunc)(int);
 45	int		users;
 46	struct list_head list;
 47};
 48
 49/**
 50 * struct rs_control - rs control structure per instance
 51 * @codec:	The codec used for this instance
 52 * @buffers:	Internal scratch buffers used in calls to decode_rs()
 53 */
 54struct rs_control {
 55	struct rs_codec	*codec;
 56	uint16_t	buffers[];
 57};
 58
 59/* General purpose RS codec, 8-bit data width, symbol width 1-15 bit  */
 60#ifdef CONFIG_REED_SOLOMON_ENC8
 61int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
 62	       uint16_t invmsk);
 63#endif
 64#ifdef CONFIG_REED_SOLOMON_DEC8
 65int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
 66		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 67	       uint16_t *corr);
 68#endif
 69
 70/* General purpose RS codec, 16-bit data width, symbol width 1-15 bit  */
 71#ifdef CONFIG_REED_SOLOMON_ENC16
 72int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
 73		uint16_t invmsk);
 74#endif
 75#ifdef CONFIG_REED_SOLOMON_DEC16
 76int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
 77		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
 78		uint16_t *corr);
 79#endif
 80
 81struct rs_control *init_rs_gfp(int symsize, int gfpoly, int fcr, int prim,
 82			       int nroots, gfp_t gfp);
 83
 84/**
 85 * init_rs - Create a RS control struct and initialize it
 86 *  @symsize:	the symbol size (number of bits)
 87 *  @gfpoly:	the extended Galois field generator polynomial coefficients,
 88 *		with the 0th coefficient in the low order bit. The polynomial
 89 *		must be primitive;
 90 *  @fcr:	the first consecutive root of the rs code generator polynomial
 91 *		in index form
 92 *  @prim:	primitive element to generate polynomial roots
 93 *  @nroots:	RS code generator polynomial degree (number of roots)
 94 *
 95 * Allocations use GFP_KERNEL.
 96 */
 97static inline struct rs_control *init_rs(int symsize, int gfpoly, int fcr,
 98					 int prim, int nroots)
 99{
100	return init_rs_gfp(symsize, gfpoly, fcr, prim, nroots, GFP_KERNEL);
101}
102
103struct rs_control *init_rs_non_canonical(int symsize, int (*func)(int),
104					 int fcr, int prim, int nroots);
105
106/* Release a rs control structure */
107void free_rs(struct rs_control *rs);
108
109/** modulo replacement for galois field arithmetics
110 *
111 *  @rs:	Pointer to the RS codec
112 *  @x:		the value to reduce
113 *
114 *  where
115 *  rs->mm = number of bits per symbol
116 *  rs->nn = (2^rs->mm) - 1
117 *
118 *  Simple arithmetic modulo would return a wrong result for values
119 *  >= 3 * rs->nn
120*/
121static inline int rs_modnn(struct rs_codec *rs, int x)
122{
123	while (x >= rs->nn) {
124		x -= rs->nn;
125		x = (x >> rs->mm) + (x & rs->nn);
126	}
127	return x;
128}
129
130#endif