lib/gen_crc64table.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Generate lookup table for the table-driven CRC64 calculation.
   4  *
   5  * gen_crc64table is executed in kernel build time and generates
   6  * lib/crc64table.h. This header is included by lib/crc64.c for
   7  * the table-driven CRC64 calculation.
   8  *
   9  * See lib/crc64.c for more information about which specification
  10  * and polynomial arithmetic that gen_crc64table.c follows to
  11  * generate the lookup table.
  12  *
  13  * Copyright 2018 SUSE Linux.
  14  *   Author: Coly Li <colyli@suse.de>
  15  */
  16 #include <inttypes.h>
  17 #include <stdio.h>
  18
  19 #define CRC64_ECMA182_POLY 0x42F0E1EBA9EA3693ULL
  20 #define CRC64_ROCKSOFT_POLY 0x9A6C9329AC4BC9B5ULL
  21
  22 static uint64_t crc64_table[256] = {0};
  23 static uint64_t crc64_rocksoft_table[256] = {0};
  24
  25 static void generate_reflected_crc64_table(uint64_t table[256], uint64_t poly)
  26 {
  27         uint64_t i, j, c, crc;
  28
  29         for (i = 0; i < 256; i++) {
  30                 crc = 0ULL;
  31                 c = i;
  32
  33                 for (j = 0; j < 8; j++) {
  34                         if ((crc ^ (c >> j)) & 1)
  35                                 crc = (crc >> 1) ^ poly;
  36                         else
  37                                 crc >>= 1;
  38                 }
  39                 table[i] = crc;
  40         }
  41 }
  42
  43 static void generate_crc64_table(uint64_t table[256], uint64_t poly)
  44 {
  45         uint64_t i, j, c, crc;
  46
  47         for (i = 0; i < 256; i++) {
  48                 crc = 0;
  49                 c = i << 56;
  50
  51                 for (j = 0; j < 8; j++) {
  52                         if ((crc ^ c) & 0x8000000000000000ULL)
  53                                 crc = (crc << 1) ^ poly;
  54                         else
  55                                 crc <<= 1;
  56                         c <<= 1;
  57                 }
  58
  59                 table[i] = crc;
  60         }
  61 }
  62
  63 static void output_table(uint64_t table[256])
  64 {
  65         int i;
  66
  67         for (i = 0; i < 256; i++) {
  68                 printf("\t0x%016" PRIx64 "ULL", table[i]);
  69                 if (i & 0x1)
  70                         printf(",\n");
  71                 else
  72                         printf(", ");
  73         }
  74         printf("};\n");
  75 }
  76
  77 static void print_crc64_tables(void)
  78 {
  79         printf("/* this file is generated - do not edit */\n\n");
  80         printf("#include <linux/types.h>\n");
  81         printf("#include <linux/cache.h>\n\n");
  82         printf("static const u64 ____cacheline_aligned crc64table[256] = {\n");
  83         output_table(crc64_table);
  84
  85         printf("\nstatic const u64 ____cacheline_aligned crc64rocksofttable[256] = {\n");
  86         output_table(crc64_rocksoft_table);
  87 }
  88
  89 int main(int argc, char *argv[])
  90 {
  91         generate_crc64_table(crc64_table, CRC64_ECMA182_POLY);
  92         generate_reflected_crc64_table(crc64_rocksoft_table, CRC64_ROCKSOFT_POLY);
  93         print_crc64_tables();
  94         return 0;
  95 }