include/linux/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@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  */
  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 */
 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