1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Generic Reed Solomon encoder / decoder library
4  *
5  * Copyright (C) 2004 Thomas Gleixner (tglx@linutronix.de)
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/list.h>
14 #include <linux/types.h>	/* for gfp_t */
15 #include <linux/gfp.h>		/* for GFP_KERNEL */
16 
17 /**
18  * struct rs_codec - rs codec data
19  *
20  * @mm:		Bits per symbol
21  * @nn:		Symbols per block (= (1<<mm)-1)
22  * @alpha_to:	log lookup table
23  * @index_of:	Antilog lookup table
24  * @genpoly:	Generator polynomial
25  * @nroots:	Number of generator roots = number of parity symbols
26  * @fcr:	First consecutive root, index form
27  * @prim:	Primitive element, index form
28  * @iprim:	prim-th root of 1, index form
29  * @gfpoly:	The primitive generator polynominal
30  * @gffunc:	Function to generate the field, if non-canonical representation
31  * @users:	Users of this structure
32  * @list:	List entry for the rs codec list
33 */
34 struct rs_codec {
35 	int		mm;
36 	int		nn;
37 	uint16_t	*alpha_to;
38 	uint16_t	*index_of;
39 	uint16_t	*genpoly;
40 	int		nroots;
41 	int		fcr;
42 	int		prim;
43 	int		iprim;
44 	int		gfpoly;
45 	int		(*gffunc)(int);
46 	int		users;
47 	struct list_head list;
48 };
49 
50 /**
51  * struct rs_control - rs control structure per instance
52  * @codec:	The codec used for this instance
53  * @buffers:	Internal scratch buffers used in calls to decode_rs()
54  */
55 struct rs_control {
56 	struct rs_codec	*codec;
57 	uint16_t	buffers[];
58 };
59 
60 /* General purpose RS codec, 8-bit data width, symbol width 1-15 bit  */
61 #ifdef CONFIG_REED_SOLOMON_ENC8
62 int encode_rs8(struct rs_control *rs, uint8_t *data, int len, uint16_t *par,
63 	       uint16_t invmsk);
64 #endif
65 #ifdef CONFIG_REED_SOLOMON_DEC8
66 int decode_rs8(struct rs_control *rs, uint8_t *data, uint16_t *par, int len,
67 		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
68 	       uint16_t *corr);
69 #endif
70 
71 /* General purpose RS codec, 16-bit data width, symbol width 1-15 bit  */
72 #ifdef CONFIG_REED_SOLOMON_ENC16
73 int encode_rs16(struct rs_control *rs, uint16_t *data, int len, uint16_t *par,
74 		uint16_t invmsk);
75 #endif
76 #ifdef CONFIG_REED_SOLOMON_DEC16
77 int decode_rs16(struct rs_control *rs, uint16_t *data, uint16_t *par, int len,
78 		uint16_t *s, int no_eras, int *eras_pos, uint16_t invmsk,
79 		uint16_t *corr);
80 #endif
81 
82 struct rs_control *init_rs_gfp(int symsize, int gfpoly, int fcr, int prim,
83 			       int nroots, gfp_t gfp);
84 
85 /**
86  * init_rs - Create a RS control struct and initialize it
87  *  @symsize:	the symbol size (number of bits)
88  *  @gfpoly:	the extended Galois field generator polynomial coefficients,
89  *		with the 0th coefficient in the low order bit. The polynomial
90  *		must be primitive;
91  *  @fcr:	the first consecutive root of the rs code generator polynomial
92  *		in index form
93  *  @prim:	primitive element to generate polynomial roots
94  *  @nroots:	RS code generator polynomial degree (number of roots)
95  *
96  * Allocations use GFP_KERNEL.
97  */
init_rs(int symsize,int gfpoly,int fcr,int prim,int nroots)98 static inline struct rs_control *init_rs(int symsize, int gfpoly, int fcr,
99 					 int prim, int nroots)
100 {
101 	return init_rs_gfp(symsize, gfpoly, fcr, prim, nroots, GFP_KERNEL);
102 }
103 
104 struct rs_control *init_rs_non_canonical(int symsize, int (*func)(int),
105 					 int fcr, int prim, int nroots);
106 
107 /* Release a rs control structure */
108 void free_rs(struct rs_control *rs);
109 
110 /** modulo replacement for galois field arithmetics
111  *
112  *  @rs:	Pointer to the RS codec
113  *  @x:		the value to reduce
114  *
115  *  where
116  *  rs->mm = number of bits per symbol
117  *  rs->nn = (2^rs->mm) - 1
118  *
119  *  Simple arithmetic modulo would return a wrong result for values
120  *  >= 3 * rs->nn
121 */
rs_modnn(struct rs_codec * rs,int x)122 static inline int rs_modnn(struct rs_codec *rs, int x)
123 {
124 	while (x >= rs->nn) {
125 		x -= rs->nn;
126 		x = (x >> rs->mm) + (x & rs->nn);
127 	}
128 	return x;
129 }
130 
131 #endif
132